Make sure the i386 sysv stack is aligned #218
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SysV ABI requires a stack alignment of 16 bytes. Currently, for i386 with SysV ABI, the trampoline function is entered with an unaligned stack. This causes problems for the context-function that is jumped to as its stack is also unaligned. This causes a crash for our use-case because the context function contains an SSE instruction which reads from the stack. The SSE instruction requires the correct alignment. Fix it by changing the 0x2c offset to 0x30, such that the stack remains aligned.
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algitbot
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Feb 5, 2024
Without this patch, boost's `make_fcontext` does not correctly align the stack pointer on i386. This will cause software to SIGSEV when using `movaps` and similar instructions which require 16-byte stack alignment. This fixes the Nix check() on x86 (see !60218). See: * boostorg/context#210 * boostorg/context#218
bell-sw
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Feb 7, 2024
[ commit b602563d3e3a4428c07eacbfde85e6e0fbe1c0f4 ] Without this patch, boost's `make_fcontext` does not correctly align the stack pointer on i386. This will cause software to SIGSEV when using `movaps` and similar instructions which require 16-byte stack alignment. This fixes the Nix check() on x86 (see !60218). See: * boostorg/context#210 * boostorg/context#218
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SysV ABI requires a stack alignment of 16 bytes. Currently, for i386 with SysV ABI, the trampoline function is entered with an unaligned stack. This causes problems for the context-function that is jumped to as its stack is also unaligned. This causes a crash for our use-case because the context function contains an SSE instruction which reads from the stack. The SSE instruction requires the correct alignment. Fix it by changing the 0x2c offset to 0x30, such that the stack remains aligned.
Related issue in this repo: #210
For reference:
php/php-src#10407 (comment) and php/php-src#10398