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How a 20 year old bug in GTA San Andreas surfaced in Windows 11 24H2

Posted: 2025-04-23 14:00:11

A 20-year-old bug in Grand Theft Auto: San Andreas, related to how the game handles specific low-level keyboard input, resurfaced in Windows 11 24H2. This bug, originally present in the 2005 release, causes the game to minimize when certain key combinations are pressed, particularly involving the right Windows key. The issue stemmed from DirectInput, a now-deprecated API used for game controllers, and wasn't previously problematic because older versions of Windows handled the spurious messages differently. Windows 11's updated input stack now surfaces these messages to the game, triggering the minimize behavior. A workaround exists by using a third-party DirectInput wrapper or running the game in compatibility mode for Windows 7.

A curious and rather amusing bug recently emerged, affecting users of Windows 11 24H2 who also happen to be fans of the classic video game Grand Theft Auto: San Andreas. This bug, dormant for two decades, resurfaced due to a specific interaction between the game and the operating system's new memory manager. The issue manifested as distorted visuals within the game, specifically corrupt textures and graphical artifacts, rendering San Andreas virtually unplayable.

The root cause can be traced back to a memory allocation technique used by the game dating back to its original 2004 release. San Andreas, optimized for older hardware and operating systems, employed a method of directly writing to specific memory addresses within the game's address space. This practice, while functional in the past, clashes with the modern memory management strategies implemented in Windows 11 24H2. The new memory manager, designed for enhanced security and efficiency, employs stricter controls over how applications access and modify memory. This stricter control inadvertently interferes with San Andreas's legacy memory access patterns.

More specifically, Windows 11 24H2's memory manager seems to misinterpret San Andreas's direct memory writes. Instead of allowing the game to modify the intended texture data, the operating system prevents or redirects these writes, leading to the corrupted visuals observed by players. The author highlights that this issue is not unique to San Andreas; other older games employing similar memory manipulation techniques could potentially exhibit similar compatibility problems on Windows 11 24H2. This underscores the challenges faced when maintaining backward compatibility with legacy software on constantly evolving operating systems.

Interestingly, the bug's manifestation isn't consistent across all hardware configurations. Some users reported no issues, while others experienced severe graphical glitches. This variability suggests that factors like specific graphics drivers or system configurations might play a role in whether the bug is triggered. The blog post meticulously details the author's investigation process, showcasing their use of debugging tools and memory analysis to pinpoint the problem's origin. Through careful observation and experimentation, they demonstrated how specific memory addresses accessed by San Andreas were being handled differently by the updated memory manager. The author concluded by suggesting potential workarounds, including running the game in compatibility mode for older Windows versions, although the effectiveness of these workarounds seemed to vary. The post serves as a fascinating example of how legacy software can unexpectedly interact with modern operating systems, highlighting the complexities of maintaining backward compatibility in the ever-evolving landscape of computer technology.

Summary of Comments ( 48 )
https://news.ycombinator.com/item?id=43772311

Commenters on Hacker News discuss the GTA San Andreas bug triggered by Windows 11 24H2, mostly focusing on the technical aspects. Several highlight the likely culprit: a change in how Windows handles thread local storage (TLS) callbacks, specifically the order of execution. One compelling comment notes the difficulty in debugging such issues, as the problem might not lie within the game's code itself, but rather in the interaction with the OS, making it hard to pinpoint and fix. Others mention the impressive longevity of the game and express surprise that such a bug could remain hidden for so long, while some jokingly lament the "progress" of Windows updates. A few commenters share their own experiences with similar obscure bugs and the challenges they posed.

The Hacker News post discussing a 20-year-old bug in GTA San Andreas surfacing in Windows 11 24H2 has several comments exploring the technical aspects and implications of the issue.

One commenter highlights the complexity of software interactions, pointing out how a seemingly unrelated change in the operating system can unexpectedly trigger dormant bugs in older applications. They emphasize the difficulty in predicting such issues, especially in large and intricate systems like Windows and a game as complex as GTA San Andreas.

Another comment delves into the specifics of the bug, explaining how the change in Windows 11's handling of specific instructions, particularly related to floating-point operations and denormalized numbers, led to the game's malfunction. This explanation provides a technical understanding of why the bug only surfaced after the Windows update.

Several commenters discuss the challenges faced by developers in maintaining backward compatibility, especially over such long periods. They note that anticipating all possible interactions between a game and future operating system updates is practically impossible. The idea of "bit rot," where software gradually degrades over time due to changes in the surrounding technological environment, is also mentioned.

One commenter mentions a similar experience with another older game, illustrating that this kind of issue isn't unique to GTA San Andreas and highlighting the broader challenge of preserving software functionality across evolving platforms.

There's a discussion about the nature of denormalized numbers and their impact on performance. One commenter questions the practical necessity of handling denormalized numbers in modern hardware and software, suggesting that their support might be more trouble than it's worth in some contexts.

Finally, a few commenters offer potential workarounds for the issue, such as disabling hardware acceleration or using compatibility modes in Windows 11. These suggestions provide practical solutions for users affected by the bug while waiting for a permanent fix.

Cursor IDE support hallucinates lockout policy, causes user cancellations

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Posted: 2025-04-14 16:24:28

A Reddit post warned Cursor IDE users about a misleading error message claiming their account was locked due to multiple logins. The message, appearing for some users even when they were only logged in on one device, falsely stated that their account was disabled and prompted them to contact support. This erroneous "lockout policy" led to confusion and user cancellations, as people believed they were genuinely blocked from using the IDE. The Cursor team acknowledged the issue, clarifying that no such lockout policy exists and attributing the problem to a bug. They assured users that their accounts were safe and worked to resolve the misleading error.

Summary of Comments ( 501 )
https://news.ycombinator.com/item?id=43683012

HN commenters were largely critical of Cursor's handling of the situation. Several pointed out the poor communication, with the "single device" restriction not being clearly conveyed and the error message misleadingly suggesting a lockout due to suspicious activity. Some saw this as a classic example of premature optimization, arguing that preventing multiple logins offered minimal benefit while alienating users. Others speculated about the technical reasons behind the restriction, suggesting it might be related to the complexity of maintaining shared state in Cursor's collaborative features. The overall sentiment was that this incident damaged Cursor's reputation and highlighted a lack of user empathy in their decision-making process.

The Hacker News comments section for the submission titled "Cursor IDE support hallucinates lockout policy, causes user cancellations" discusses the situation where Cursor IDE's support incorrectly claimed a single-login policy was in effect, leading to user confusion and cancellations.

Several commenters express skepticism about the veracity of the Reddit post that sparked the discussion. They question whether the support agent truly misunderstood the situation, suggesting alternative explanations such as the user potentially having multiple accounts or encountering a temporary bug. One commenter points out the unprofessional nature of the support interaction, highlighting the lack of a clear explanation from Cursor and the dismissive tone used with the user.

A significant thread emerges around the business model of Cursor IDE and whether its reliance on OpenAI's APIs makes it vulnerable to high operational costs. Commenters debate the sustainability of building a business solely on top of another company's API, with some arguing that the high costs of these APIs could lead to aggressive pricing strategies or even sudden changes that impact dependent businesses like Cursor. This discussion touches on the broader trend of AI-powered tools and the challenges of managing costs while providing a valuable service.

Some commenters draw parallels to other coding assistance tools, discussing the competitive landscape and how Cursor's features and pricing compare to alternatives like GitHub Copilot. The issue of pricing is a recurring theme, with some users questioning the value proposition of Cursor given the availability of other, potentially more affordable options.

Another line of discussion focuses on the technical aspects of Cursor and its usage of OpenAI's APIs. Commenters speculate on the potential reasons for the login issue, including possibilities like IP address conflicts, session management problems, or even misinterpretations of usage data. This technical discussion adds another layer to the conversation, moving beyond the immediate customer service issue and delving into the potential underlying technical challenges faced by Cursor.

Finally, some comments express general frustration with the current state of AI-powered coding tools, citing issues like inaccuracies, hallucinations, and the potential for over-reliance on these tools. This broader sentiment reflects some of the ongoing concerns about the implications of AI in software development. Overall, the comments section presents a multifaceted discussion about the incident, covering customer support, business models, technical challenges, and the broader impact of AI in the coding landscape.

Shenmue (1999) Reverse Engineering Reveals Possible Sun Position Oversight

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Posted: 2025-03-12 17:00:28

Reverse engineering of Shenmue's source code revealed that the sun's position in the game is calculated using a simplified formula that doesn't account for axial tilt or the equation of time. This results in the sun rising and setting slightly earlier than it should in the game's real-world counterpart of Yokosuka, Japan, across all in-game dates. While noticeable, this discrepancy doesn't significantly impact gameplay and may have been a deliberate simplification for performance reasons on the Dreamcast. The author speculates whether it qualifies as a "bug" given its likely intentional nature and minimal effect on the overall experience.

The blog post "Shenmue (1999) Reverse Engineering Reveals Possible Sun Position Oversight" by Matthew Earl delves into a detailed technical analysis of the sun's behavior within the classic Dreamcast game, Shenmue. Earl, driven by a meticulous curiosity about the game's inner workings, leverages reverse engineering techniques to dissect the code governing the sun's position. He specifically examines the game's calculation of solar altitude and azimuth, the two angles that define the sun's location in the sky. Through painstaking examination of the disassembled game code, Earl reconstructs the mathematical formulas employed by the game to determine these angles. He discovers that the game utilizes a simplified solar positioning algorithm, which, while computationally efficient for the hardware of the time, exhibits certain discrepancies when compared to more realistic models of solar movement.

The crux of the post centers around a specific anomaly uncovered through this reverse engineering process: the game appears to calculate the sun's azimuth angle based solely on the in-game time of day, seemingly disregarding the date or season. This simplification, Earl posits, could lead to inaccuracies in the sun's apparent position in the sky, particularly noticeable during the transitional periods between seasons. He meticulously demonstrates this potential discrepancy by contrasting the game's calculated sun position with the expected solar position for Yokosuka, Japan (the real-world location upon which Shenmue's setting is based) on specific dates and times. While acknowledging the inherent limitations of the Dreamcast's hardware and the necessity for performance optimization, Earl raises the question of whether this simplification represents a conscious design choice or an unintentional oversight. He meticulously refrains from definitively labeling it a "bug," instead presenting the analysis as an exploration of the game's internal workings and the potential implications of its simplified approach to simulating celestial mechanics. The post ultimately serves as a fascinating glimpse into the complexities of game development, highlighting the trade-offs developers often face between realism and performance, and showcasing the power of reverse engineering as a tool for understanding these intricate decisions.

Summary of Comments ( 16 )
https://news.ycombinator.com/item?id=43345285

Hacker News users discuss whether the perceived sun position error in Shenmue is actually a bug or a deliberate design choice. Some commenters suggest it's a performance optimization, avoiding complex calculations for marginally improved visuals. Others argue it's simply a bug, pointing to inconsistencies with the in-game clock and world design. Several discuss the challenges of reverse engineering older games, particularly with limited documentation, and the difficulty of definitively labeling something a bug without access to the original source code and developer intentions. The discussion also touches on the nostalgic appeal of Shenmue and the dedication of its fan community in dissecting the game's intricacies.

The Hacker News post about a potential sun position oversight in Shenmue generated several interesting comments.

One commenter pointed out that the game's use of pre-calculated lighting and shadows was a common technique in the late 90s due to hardware limitations. They suggested that the discrepancy in sun position might be a deliberate simplification made to optimize performance. This comment also discussed the challenges of realistically simulating time of day in games, noting that even modern games sometimes struggle with accurate sun and shadow behavior.

Another commenter shared a personal anecdote about working with a former Sega developer. This anecdote highlighted the common practice of "good enough" approximations in game development, especially during that era. They argued that minor inconsistencies like the sun position issue were often overlooked in favor of meeting deadlines and staying within performance constraints.

Several commenters discussed the technical details of how the sun's position is typically calculated in games, including the use of spherical coordinates and transformation matrices. These discussions provided further context for understanding the potential source of the discrepancy in Shenmue. One comment even speculated about the specific code or algorithms that might have been used by the developers.

One commenter mentioned the "You're not supposed to see that" phenomenon often encountered in games. This highlights how developers often prioritize creating the intended player experience over perfect realism, accepting minor inconsistencies that are unlikely to be noticed by most players.

Finally, some commenters expressed admiration for the original poster's dedication to reverse engineering and analyzing the game's inner workings. They appreciated the insight into the technical challenges faced by game developers, particularly during the Dreamcast era.

Overall, the comments section provided a mix of technical explanations, historical context, and personal anecdotes that helped shed light on the potential sun position oversight in Shenmue. The commenters generally agreed that the issue was likely a deliberate simplification or a minor bug, rather than a significant flaw in the game's design.

A Clang regression related to switch statements and inlining

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Posted: 2025-02-18 12:38:08

A recent Clang optimization introduced in version 17 regressed performance when compiling code containing large switch statements within inlined functions. This regression manifested as significantly increased compile times, sometimes by orders of magnitude, and occasionally resulted in internal compiler errors. The issue stems from Clang's attempt to optimize switch lowering by transforming it into a series of conditional moves based on jump tables. This optimization, while beneficial in some cases, interacts poorly with inlining, exploding the complexity of the generated intermediate representation (IR) when a function with a large switch is inlined multiple times. This ultimately overwhelms the compiler's later optimization passes. A workaround involves disabling the problematic optimization via a compiler flag (-mllvm -switch-to-lookup-table-threshold=0) until a proper fix is implemented in a future Clang release.

This blog post details a performance regression discovered by the author, Adrian Nicula, in Clang versions 15 and 16 concerning the compilation of C++ code containing large switch statements within inline functions. The issue arises specifically when these switch statements are located inside inline functions that are called repeatedly within a hot loop. Prior to Clang 15, the compiler effectively optimized these scenarios, resulting in efficient code execution. However, in Clang 15 and 16, the optimization strategy changed, leading to a significant performance degradation in specific circumstances.

The core problem stems from how Clang handles jump tables, a common optimization technique for switch statements. Previously, when an inline function with a large switch was called repeatedly, Clang would generate a single jump table for the switch statement and reuse it across all call sites. This approach minimized code size and maximized performance.

Beginning with Clang 15, the compiler seemingly changed its inlining heuristics. Instead of creating a single shared jump table, Clang now generates a separate jump table for each instance of the inlined function within the loop. This duplication significantly increases the code size, particularly for large switch statements with numerous cases. The larger code size negatively impacts instruction cache performance, leading to the observed performance regression.

Nicula demonstrates the issue with a concise example involving a benchmarking program that measures the execution time of code containing a large switch statement within an inline function. He provides performance measurements across different Clang versions, clearly showing the performance drop in versions 15 and 16. The benchmark also highlights that the issue only manifests when the inline function is called a substantial number of times within a loop.

The author further investigates the generated assembly code, confirming the proliferation of jump tables in Clang 15 and 16 compared to earlier versions. This analysis solidifies the hypothesis that the change in jump table generation is the root cause of the performance problem.

While Nicula did not pinpoint the exact commit introducing this regression, he suspects it may be related to modifications in Clang's inlining or jump table generation logic around the time of Clang 15's release. The author concludes by recommending users experiencing similar performance issues to revert to Clang 14 or explore compiler flags related to inlining and optimization to potentially mitigate the problem. He also expresses hope that the Clang community will address this regression in future releases.

Summary of Comments ( 2 )
https://news.ycombinator.com/item?id=43088797

The Hacker News comments discuss a performance regression in Clang involving large switch statements and inlining. Several commenters confirm experiencing similar issues, particularly when compiling large codebases. Some suggest the regression might be related to changes in the inlining heuristics or the way Clang handles jump tables. One commenter points out that using a constexpr hash table for large switches can be a faster alternative. Another suggests profiling and selective inlining as a workaround. The lack of clear identification of the root cause and the potential impact on compile times and performance are highlighted as concerning. Some users express frustration with the frequency of such regressions in Clang.

The Hacker News post discussing the Clang regression related to switch statements and inlining sparked a conversation revolving primarily around compiler optimization, code generation, and debugging challenges. Several commenters delved into the technical intricacies of the issue.

One commenter highlighted the complexities involved in compiler optimization, specifically mentioning the difficulty in striking a balance between performance gains and potential code bloat. They pointed out that aggressive inlining, while often beneficial, can sometimes lead to larger binaries and potentially slower execution in certain scenarios, as was seemingly the case with the Clang regression described in the article. This commenter also touched upon the trade-offs compilers must make and how these decisions can sometimes have unforeseen consequences.

Another commenter focused on the debugging challenges introduced by such optimizations. They argued that overly aggressive inlining can obscure the relationship between the original source code and the generated assembly, making it harder to debug issues. This difficulty stems from the fact that the inlined code is effectively "merged" into the calling function, making it harder to trace back to the original source location when stepping through a debugger.

The discussion also touched upon the specifics of switch statement optimization. One commenter explained how compilers often transform switch statements into various forms, such as jump tables or binary search trees, depending on the density and distribution of the cases. They suggested that the Clang regression might be related to a suboptimal choice of switch implementation in specific scenarios.

Furthermore, a commenter mentioned the importance of profiling and benchmarking in identifying and addressing such performance regressions. They emphasized that relying solely on theoretical analysis of code transformations can be misleading and that empirical data is crucial for understanding the actual impact of compiler optimizations.

Finally, some commenters discussed potential workarounds and suggested exploring compiler flags to fine-tune inlining behavior or to disable specific optimizations. This highlighted the importance of having granular control over the compiler's optimization strategies to mitigate potential performance issues.

Overall, the comments on Hacker News provided valuable insights into the technical nuances of the Clang regression, focusing on the challenges related to compiler optimization, debugging, and the importance of profiling and benchmarking. The discussion demonstrated a deep understanding of compiler internals and offered practical suggestions for dealing with similar issues.

The dumb reason why flag emojis aren't working on your site in Chrome on Windows

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Posted: 2025-01-29 23:44:35

Some websites display boxes instead of flag emojis in Chrome on Windows due to a font substitution issue. Windows uses its own Segoe UI Emoji font for most emoji, but defaults to a lower-quality bitmap font called "Segoe UI Symbol" specifically for flag emojis. This bitmap font lacks the necessary glyphs for many flag combinations, resulting in the missing emoji. Websites can force Chrome to use the correct, vector-based Segoe UI Emoji font by explicitly specifying it in their CSS, ensuring flags render properly.

Matthias Geyer's blog post, "The dumb reason why flag emojis aren't working on your site in Chrome on Windows," delves into a perplexing issue where flag emojis fail to render correctly in the Google Chrome web browser specifically on Windows operating systems. The problem manifests as a sequence of two separate emoji characters appearing instead of the desired single flag emoji. For example, instead of the cohesive British flag emoji, a user might see the Great Britain "GB" letters emoji followed by a waving white flag emoji.

Geyer meticulously explains that this anomaly stems from a discrepancy in how different systems handle flag emojis. Flag emojis are technically not individual characters in the Unicode standard. Instead, they are constructed dynamically by combining two regional indicator symbol letters (RILS), essentially representing the two-letter ISO country code, with a special zero-width joiner (ZWJ) character. This ZWJ instructs the system to combine the two preceding characters into a single, visually unified flag glyph.

The crux of the issue lies within the Segoe UI Emoji font, the default emoji font employed by Windows. This font lacks the necessary glyphs to render the composite flag emoji. While Segoe UI Emoji does contain individual glyphs for the two-letter regional indicators, it does not include the combined, finalized flag glyphs themselves. Consequently, when Chrome on Windows encounters a flag emoji sequence, it correctly interprets the RILS and ZWJ sequence, but due to the missing glyph in Segoe UI Emoji, it falls back to displaying the individual RILS characters followed by a generic white flag emoji as a placeholder for the missing combined glyph. This results in the broken flag emoji display.

Geyer further elaborates that other operating systems and browsers handle this scenario differently. Systems like macOS, iOS, and Android, along with browsers like Firefox on Windows, possess more complete emoji fonts that do include the unified flag glyphs. Hence, these systems correctly render flag emojis as intended.

He concludes by suggesting a potential workaround for web developers facing this issue: explicitly specifying a cross-platform emoji font like Noto Emoji or Twemoji in the website's CSS styles. By enforcing the use of a font that contains the necessary flag glyphs, the issue can be circumvented, ensuring consistent flag emoji display across different operating systems and browsers. This allows for a more uniform user experience, preventing the fragmented and confusing display of broken flag emojis specifically on Windows systems using Chrome.

Summary of Comments ( 23 )
https://news.ycombinator.com/item?id=42872882

Commenters on Hacker News largely discuss the technical details behind the issue, focusing on the surprising interaction between Chrome, Windows, and the specific way flags are rendered using two combined code points. Several point out the complexity and unexpected behaviors that arise from combining characters, particularly when dealing with different systems and fonts. Some users express frustration with the inconsistency and lack of clear documentation around emoji rendering. A few commenters offer potential workarounds or solutions, including using a fallback font or pre-rendering the flags as images. Others delve into the history and evolution of emoji standards and the challenges of maintaining compatibility across platforms. A compelling comment thread explores the tradeoffs between using the combined code points for flags versus using dedicated single code points, highlighting the performance implications and rendering complexities. Another interesting discussion revolves around the role of fonts and the challenges of designing fonts that support a rapidly expanding set of emojis.

The Hacker News post titled "The dumb reason why flag emojis aren't working on your site in Chrome on Windows" generated a moderate discussion with several insightful comments.

Many commenters corroborated the author's findings about the issue with flag emojis rendering as two-letter country codes on Windows Chrome when using the Segoe UI Emoji font. They shared their experiences and frustrations with this inconsistency across different operating systems and browsers. Some highlighted the challenges this poses for web developers who aim for consistent user experience regardless of the platform.

Several commenters delved into the technical details behind the issue. Some pointed out the difference between Segoe UI Emoji font being the default for emoji rendering in Windows applications versus the browser's handling of fonts, especially in relation to system settings. One comment speculated on potential performance implications of using the system emoji font in Chrome, suggesting it could lead to slower rendering compared to using a bundled font.

A particularly compelling comment thread discussed the complexities of Unicode and emoji rendering, noting that "flag emojis" aren't technically single emojis but rather sequences of regional indicator symbols. This explained why different systems handle them differently depending on their font support and rendering engines. This thread further explored the limitations and ambiguities inherent in representing flags as emojis, given the evolving political landscape and changing national symbols.

Other comments offered practical workarounds, such as using a dedicated emoji font or CSS tricks to ensure consistent emoji display. Some suggested using SVG images of flags as a more robust solution, albeit with potential drawbacks related to accessibility and file size.

A few commenters expressed skepticism about the significance of the issue, arguing that consistent emoji rendering is a minor concern compared to other web development challenges. However, others countered that even seemingly small UI inconsistencies can detract from the user experience and create confusion.

Overall, the comments provided a mix of technical insights, practical advice, and diverse opinions on the importance of consistent emoji rendering across different platforms. The discussion highlighted the complexities of Unicode, font rendering, and the challenges faced by web developers in achieving cross-platform compatibility.

Google Pixel 4a's old firmware is gone, trapping users on buggy battery update

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Posted: 2025-01-29 14:59:59

Pixel 4a owners who haven't updated their phones are now stuck with a buggy December 2022 battery update as Google has removed older firmware versions from its servers. This means users can no longer downgrade to escape the battery drain and random shutdown issues introduced by the update. While Google has acknowledged the problem and promised a fix, there's no ETA, leaving affected users with no immediate solution. Essentially, Pixel 4a owners are forced to endure the battery problems until Google releases the corrected update.

Summary of Comments ( 156 )
https://news.ycombinator.com/item?id=42865619

HN commenters generally express frustration and disappointment with Google's handling of the Pixel 4a battery issue. Several users report experiencing the battery drain problem after the update, with some claiming significantly reduced battery life. Some criticize Google's lack of communication and the removal of older firmware, making it impossible to revert to a working version. Others discuss potential workarounds, including custom ROMs like LineageOS, but acknowledge the risks and technical knowledge required. A few commenters mention the declining quality control of Pixel phones and question Google's commitment to supporting older devices. The overall sentiment is negative, with many expressing regret over purchasing a Pixel phone and a loss of trust in Google's hardware division.

The Hacker News comments section for the submitted Android Central article, "Google Pixel 4a's old firmware is gone, trapping users on the buggy battery update," contains a moderate number of comments discussing the situation. Several users express frustration and disappointment with Google's handling of the Pixel 4a battery issue.

A recurring theme is the lack of official acknowledgment or solution from Google. Commenters point out the silence from Google regarding the problem, despite widespread reports of significantly reduced battery life following the update. This lack of communication is seen as particularly concerning, leaving users feeling abandoned and unsure of whether a fix is forthcoming.

Some users share their personal experiences with the battery drain issue, corroborating the article's claims. They detail how their phone's battery life has drastically decreased, impacting their daily usage. One commenter mentions attempting various troubleshooting steps, including factory resets, but to no avail. This reinforces the severity of the issue and the lack of effective workarounds.

The unavailability of older firmware versions is a major point of contention. Commenters lament the inability to roll back to a previous, more stable firmware, effectively trapping them with the buggy update. This is contrasted with the practices of other manufacturers, like Apple, who often allow users to revert to older iOS versions if problems arise. The removal of older Pixel 4a firmware is viewed as a significant misstep by Google, limiting user options and exacerbating the battery issue.

Several commenters express broader concerns about the decreasing quality and support of Pixel phones. They perceive a trend of declining software quality and customer service, leading to disillusionment with the Pixel brand. Some mention considering switching to other Android manufacturers or even to iPhones due to these perceived shortcomings.

The overall sentiment in the comments section is one of negativity towards Google's handling of the Pixel 4a battery issue. Users express frustration with the lack of communication, the absence of a solution, and the inability to downgrade to older firmware. This experience appears to be eroding confidence in the Pixel brand for some users.

An invalid 68030 instruction accidentally allowed the Mac Classic II to boot

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Posted: 2025-01-25 20:29:41

A quirk in the Motorola 68030 processor inadvertently enabled the Mac Classic II to boot despite its ROM lacking proper 32-bit addressing support. The Classic II's ROM mistakenly used a "MOVEA" instruction with a 32-bit address, which should have caused a failure on the 24-bit address bus. However, the 68030, when configured for a 24-bit bus, ignores the upper byte of the 32-bit address in this specific instruction. This unintentional compatibility allowed the flawed ROM to function, making the Classic II's boot process seemingly normal despite the underlying programming error.

Doug Brown's blog post, "An invalid 68030 instruction accidentally allowed the Mac Classic II to successfully boot up," details a fascinating discovery related to the boot process of the Mac Classic II. This compact Macintosh model, released in 1991, utilized the Motorola 68030 processor. Brown, an enthusiast of retro computing, was investigating a peculiar behavior he observed while experimenting with the machine.

The Classic II, as shipped, is equipped with a specific ROM chip. Brown had replaced this original ROM with a modified one. This modified ROM contained code designed to patch certain aspects of the system software. During the boot sequence with this modified ROM, an unexpected and seemingly erroneous instruction was being executed on the 68030 processor. This instruction, specifically a "MOVE from SR," attempted to move the contents of the status register (SR), a critical processor register holding flags and other control bits, into a data register. According to official Motorola documentation, this particular form of the instruction, involving a direct move from the status register, is undefined and should not function correctly on a 68030. One would typically expect such an illegal instruction to trigger an exception, halting the boot process.

Remarkably, instead of crashing, the Mac Classic II continued to boot successfully. Brown's meticulous investigation revealed that, due to a specific quirk in the 68030's microcode implementation on the Classic II, this normally invalid instruction was actually being interpreted and executed as a legal, albeit different, instruction: "MOVE from CCR." The CCR, or Condition Code Register, is a subset of the larger SR, holding only the condition code flags. This unintentional substitution allowed the boot process to proceed unimpeded, despite the presence of the erroneous instruction.

Furthermore, Brown discovered that the errant "MOVE from SR" instruction was a remnant of code designed for older Macintosh models that used the Motorola 68000 processor. On the 68000, this instruction was valid. When the ROM code was adapted for the 68030-based Classic II, this particular instruction was inadvertently left unchanged.

The serendipitous outcome, where an invalid instruction was misinterpreted as a valid one with similar functionality, highlights the subtle complexities and occasional unintended behaviors that can arise within computer systems. It underscores how seemingly minor differences in processor microcode can have significant, and sometimes unexpected, consequences. The incident provided a unique learning experience for Brown, shedding light on the intricacies of the Mac Classic II's hardware and the legacy code it ran.

Summary of Comments ( 1 )
https://news.ycombinator.com/item?id=42824562

Hacker News commenters on the Mac Classic II boot anomaly generally express fascination with the technical details and the serendipitous nature of the discovery. Several commenters delve into the specifics of 680x0 instruction sets and how an invalid instruction could inadvertently lead to a successful boot, speculating about memory initialization and undocumented behavior. Some share anecdotes about similar unexpected behaviors encountered during their own retrocomputing explorations. A few commenters also highlight the importance of such stories in preserving computer history and understanding the quirks of older hardware. The overall sentiment reflects appreciation for the ingenuity and occasional happy accidents that shaped early computing.

The Hacker News post discussing the article "The invalid 68030 instruction that accidentally allowed the Mac Classic II to boot" has generated several interesting comments.

Several users discuss the nature of the undocumented movc instruction and its behavior on different Motorola 680x0 processors. One user highlights the difference between the 68020 and 68030 behavior regarding the CCR and SR registers, pointing out that setting specific bits in the SR unintentionally enables MMU functionality on the 68030, which wasn't intended for the Classic II. This accidental side effect is what allowed the machine to boot. The discussion expands to cover how these subtleties often lead to unexpected discoveries in computing.

Another commenter reminisces about working with early Macintosh ROMs and the challenges of debugging without source code or comprehensive documentation. They mention the use of disassemblers and the process of painstakingly figuring out the purpose of various memory locations and instructions.

A separate thread delves into the specific MMU configuration enabled by the errant instruction. Commenters analyze the resulting address mapping and speculate on how this setup might impact performance and memory access. They also discuss the implications of running code designed for a simpler memory model on a system with an active MMU.

One user shares an anecdote about a similar "happy accident" in embedded systems development, where an undocumented behavior of a peripheral chip led to a performance boost. They draw a parallel with the Mac Classic II situation, emphasizing how unintended consequences can sometimes have positive outcomes.

The conversation also touches upon the broader history of Macintosh development and the constraints faced by engineers at the time. One comment mentions the limited resources and tight deadlines that often led to unconventional solutions and "hacks."

Finally, several comments simply express appreciation for the article and the insights it provides into the inner workings of early Macintosh hardware. They praise the author's ability to explain complex technical details in a clear and engaging manner.

Stories with Tag bug

How a 20 year old bug in GTA San Andreas surfaced in Windows 11 24H2

Summary of Comments ( 48 ) https://news.ycombinator.com/item?id=43772311

Cursor IDE support hallucinates lockout policy, causes user cancellations

Summary of Comments ( 501 ) https://news.ycombinator.com/item?id=43683012

Shenmue (1999) Reverse Engineering Reveals Possible Sun Position Oversight

Summary of Comments ( 16 ) https://news.ycombinator.com/item?id=43345285

A Clang regression related to switch statements and inlining

Summary of Comments ( 2 ) https://news.ycombinator.com/item?id=43088797

The dumb reason why flag emojis aren't working on your site in Chrome on Windows

Summary of Comments ( 23 ) https://news.ycombinator.com/item?id=42872882

Google Pixel 4a's old firmware is gone, trapping users on buggy battery update

Summary of Comments ( 156 ) https://news.ycombinator.com/item?id=42865619

An invalid 68030 instruction accidentally allowed the Mac Classic II to boot

Summary of Comments ( 1 ) https://news.ycombinator.com/item?id=42824562

Summary of Comments ( 48 )
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Summary of Comments ( 1 )
https://news.ycombinator.com/item?id=42824562