[llvm-exegesis] Use correct rseq struct size #100804
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Glibc v2.40 changes the definition of __rseq_size to the usable area of the struct rather than the actual size of the struct to accommodate users trying to figure out what features can be used. This change breaks llvm-exegesis trying to disable rseq as the size registered in the kernel is no longer equal to __rseq_size. This patch adds a check to see if __rseq_size is less than 32 bytes and uses 32 as a value if it is given alignment requirements. Fixes llvm#100791.
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@llvm/pr-subscribers-tools-llvm-exegesis Author: Aiden Grossman (boomanaiden154) ChangesGlibc v2.40 changes the definition of __rseq_size to the usable area of the struct rather than the actual size of the struct to accommodate users trying to figure out what features can be used. This change breaks llvm-exegesis trying to disable rseq as the size registered in the kernel is no longer equal to __rseq_size. This patch adds a check to see if __rseq_size is less than 32 bytes and uses 32 as a value if it is given alignment requirements. Fixes #100791. Full diff: https://github.com/llvm/llvm-project/pull/100804.diff 1 Files Affected:
diff --git a/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp b/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp
index ed53f8fabb175..adee869967d98 100644
--- a/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp
+++ b/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp
@@ -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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@mgorny Can you apply this locally and test that this fixes the issue that you saw? I don't have glibc 2.40 on a machine with perf counters available to test. |
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Sure, will do, but probably tomorrow. |
mgorny
approved these changes
Jul 27, 2024
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/cherry-pick 1e8df9e |
llvmbot
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Jul 27, 2024
Glibc v2.40 changes the definition of __rseq_size to the usable area of the struct rather than the actual size of the struct to accommodate users trying to figure out what features can be used. This change breaks llvm-exegesis trying to disable rseq as the size registered in the kernel is no longer equal to __rseq_size. This patch adds a check to see if __rseq_size is less than 32 bytes and uses 32 as a value if it is given alignment requirements. Fixes llvm#100791. (cherry picked from commit 1e8df9e)
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/pull-request #100885 |
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Failed to create pull request for issue100804 https://github.com/llvm/llvm-project/actions/runs/10125556000 |
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/cherry-pick 1e8df9e |
llvmbot
pushed a commit
to llvmbot/llvm-project
that referenced
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Jul 27, 2024
Glibc v2.40 changes the definition of __rseq_size to the usable area of the struct rather than the actual size of the struct to accommodate users trying to figure out what features can be used. This change breaks llvm-exegesis trying to disable rseq as the size registered in the kernel is no longer equal to __rseq_size. This patch adds a check to see if __rseq_size is less than 32 bytes and uses 32 as a value if it is given alignment requirements. Fixes llvm#100791. (cherry picked from commit 1e8df9e)
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/pull-request #100896 |
tru
pushed a commit
to llvmbot/llvm-project
that referenced
this pull request
Jul 29, 2024
Glibc v2.40 changes the definition of __rseq_size to the usable area of the struct rather than the actual size of the struct to accommodate users trying to figure out what features can be used. This change breaks llvm-exegesis trying to disable rseq as the size registered in the kernel is no longer equal to __rseq_size. This patch adds a check to see if __rseq_size is less than 32 bytes and uses 32 as a value if it is given alignment requirements. Fixes llvm#100791. (cherry picked from commit 1e8df9e)
Ma27
added a commit
to Ma27/nixpkgs
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Sep 15, 2024
See llvm/llvm-project#100804 for further context. Tests for LLVM 12 to 16 pass fine without this change (the entire section of the test doesn't exist there), our LLVM 19 already has the patch applied.
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Glibc v2.40 changes the definition of __rseq_size to the usable area of the struct rather than the actual size of the struct to accommodate users trying to figure out what features can be used. This change breaks llvm-exegesis trying to disable rseq as the size registered in the kernel is no longer equal to __rseq_size. This patch adds a check to see if __rseq_size is less than 32 bytes and uses 32 as a value if it is given alignment requirements.
Fixes #100791.