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[llvm-exegesis] Use correct rseq struct size #100804

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Jul 27, 2024
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[llvm-exegesis] Use correct rseq struct size #100804

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13 changes: 12 additions & 1 deletion llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -466,9 +466,20 @@ class SubProcessFunctionExecutorImpl
// segfaults in the program. Unregister the rseq region so that we can safely
// unmap it later
#ifdef GLIBC_INITS_RSEQ
unsigned int RseqStructSize = __rseq_size;

// Glibc v2.40 (the change is also expected to be backported to v2.35)
// changes the definition of __rseq_size to be the usable area of the struct
// rather than the actual size of the struct. v2.35 uses only 20 bytes of
// the 32 byte struct. For now, it should be safe to assume that if the
// usable size is less than 32, the actual size of the struct will be 32
// bytes given alignment requirements.
if (__rseq_size < 32)
RseqStructSize = 32;

long RseqDisableOutput =
syscall(SYS_rseq, (intptr_t)__builtin_thread_pointer() + __rseq_offset,
__rseq_size, RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
RseqStructSize, RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
if (RseqDisableOutput != 0)
exit(ChildProcessExitCodeE::RSeqDisableFailed);
#endif // GLIBC_INITS_RSEQ
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