Fix GH-10908: Bus error with PDO Firebird on RPI with 64 bit kernel and 32 bit userland #10920
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…l and 32 bit userland The alignment of sqldata is in most cases only the basic alignment, so the code type-puns it to a larger type, it *can* crash due to the misaligned access. This is only an issue for types > 4 bytes because every sensible system requires an alignment of at least 4 bytes for allocated data. Even though this patch uses memcpy, the compiler is smart enough to optimise it to something more efficient, especially on x86. This is just the usual approach to solve these alignment problems. Actually, unaligned memory access is undefined behaviour, so even on x86 platforms, where the bug doesn't cause a crash, this can be problematic. Furthermore, even though the issue talks about a 64-bit kernel and 32-bit userspace, this doesn't necessarily need to be the case to trigger this crash. Test was Co-authored-by: rvk01
nielsdos
changed the title
|
I've checked this again and I think I got everything now. Issue reporter is running the patch on their production system right now and so far no issues. |
Girgias
reviewed
Mar 26, 2023
|
Extended the test to test all our supported types. |
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The alignment of sqldata is in most cases only the basic alignment, so the code type-puns it to a larger type, it can crash due to the misaligned access. This is only an issue for types > 4 bytes because every sensible system requires an alignment of at least 4 bytes for allocated data.
Even though this patch uses memcpy, the compiler is smart enough to optimise it to something more efficient, especially on x86. This is just the usual approach to solve these alignment problems.
Actually, unaligned memory access is undefined behaviour, so even on x86 platforms, where the bug doesn't cause a crash, this can be problematic. Furthermore, even though the issue talks about a 64-bit kernel and 32-bit userspace, this doesn't necessarily need to be the case to trigger this crash.
Test was Co-authored-by: rvk01