[SampleFDO] Extend the function base name max size #135863
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@llvm/pr-subscribers-pgo Author: Lei Wang (wlei-llvm) ChangesThe function base name could be way long which leads to a crash. Update to extend the max size. Also changed to use dynamic allocation( Full diff: https://github.com/llvm/llvm-project/pull/135863.diff 1 Files Affected:
diff --git a/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp b/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
index d6d1b7c51d4c0..963c321772d6e 100644
--- a/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
+++ b/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
@@ -737,11 +737,11 @@ bool SampleProfileMatcher::functionMatchesProfileHelper(
auto FunctionName = FName.str();
if (Demangler.partialDemangle(FunctionName.c_str()))
return std::string();
- constexpr size_t MaxBaseNameSize = 4096;
- char BaseNameBuf[MaxBaseNameSize] = {};
+ constexpr size_t MaxBaseNameSize = 65536;
+ std::vector<char> BaseNameBuf(MaxBaseNameSize, 0);
size_t BaseNameSize = MaxBaseNameSize;
char *BaseNamePtr =
- Demangler.getFunctionBaseName(BaseNameBuf, &BaseNameSize);
+ Demangler.getFunctionBaseName(BaseNameBuf.data(), &BaseNameSize);
return (BaseNamePtr && BaseNameSize)
? std::string(BaseNamePtr, BaseNameSize)
: std::string();
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Member
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@llvm/pr-subscribers-llvm-transforms Author: Lei Wang (wlei-llvm) ChangesThe function base name could be way long which leads to a crash. Update to extend the max size. Also changed to use dynamic allocation( Full diff: https://github.com/llvm/llvm-project/pull/135863.diff 1 Files Affected:
diff --git a/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp b/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
index d6d1b7c51d4c0..963c321772d6e 100644
--- a/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
+++ b/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
@@ -737,11 +737,11 @@ bool SampleProfileMatcher::functionMatchesProfileHelper(
auto FunctionName = FName.str();
if (Demangler.partialDemangle(FunctionName.c_str()))
return std::string();
- constexpr size_t MaxBaseNameSize = 4096;
- char BaseNameBuf[MaxBaseNameSize] = {};
+ constexpr size_t MaxBaseNameSize = 65536;
+ std::vector<char> BaseNameBuf(MaxBaseNameSize, 0);
size_t BaseNameSize = MaxBaseNameSize;
char *BaseNamePtr =
- Demangler.getFunctionBaseName(BaseNameBuf, &BaseNameSize);
+ Demangler.getFunctionBaseName(BaseNameBuf.data(), &BaseNameSize);
return (BaseNamePtr && BaseNameSize)
? std::string(BaseNamePtr, BaseNameSize)
: std::string();
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HighW4y2H3ll
approved these changes
Apr 15, 2025
amharc
added a commit
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Apr 28, 2025
Currently the backing buffer of a `std::vector<char>` is passed[1] to `Demangler.getFunctionBaseName`. However, deeply inside the call stack `OutputBuffer::grow` will call[2] `std::realloc` if it needs to grow the buffer, leading to UB. The demangler APIs specify[3] that "`Buf` and `N` behave like the second and third parameters to `__cxa_demangle`" and the docs for the latter say[4] that the output buffer must be allocated with `malloc` (but can also be `NULL` and will then be realloced accordingly). Note: PR #135863 changed this from a stack array to a `std::vector` and increased the size to 65K, but this can still lead to a crash if the demangled name is longer than that - yes, I'm surprised that a >65K-long function name happens in practice... [1]: https://github.com/llvm/llvm-project/blob/d7e631c7cd6d9c13b9519991ec6becf08bc6b8aa/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp#L744 [2]: https://github.com/llvm/llvm-project/blob/d7e631c7cd6d9c13b9519991ec6becf08bc6b8aa/llvm/include/llvm/Demangle/Utility.h#L50 [3]: https://github.com/llvm/llvm-project/blob/d7e631c7cd6d9c13b9519991ec6becf08bc6b8aa/llvm/include/llvm/Demangle/Demangle.h#L92-L93 [4]: https://gcc.gnu.org/onlinedocs/libstdc++/libstdc++-html-USERS-4.3/a01696.html
IanWood1
pushed a commit
to IanWood1/llvm-project
that referenced
this pull request
May 6, 2025
Currently the backing buffer of a `std::vector<char>` is passed[1] to `Demangler.getFunctionBaseName`. However, deeply inside the call stack `OutputBuffer::grow` will call[2] `std::realloc` if it needs to grow the buffer, leading to UB. The demangler APIs specify[3] that "`Buf` and `N` behave like the second and third parameters to `__cxa_demangle`" and the docs for the latter say[4] that the output buffer must be allocated with `malloc` (but can also be `NULL` and will then be realloced accordingly). Note: PR llvm#135863 changed this from a stack array to a `std::vector` and increased the size to 65K, but this can still lead to a crash if the demangled name is longer than that - yes, I'm surprised that a >65K-long function name happens in practice... [1]: https://github.com/llvm/llvm-project/blob/d7e631c7cd6d9c13b9519991ec6becf08bc6b8aa/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp#L744 [2]: https://github.com/llvm/llvm-project/blob/d7e631c7cd6d9c13b9519991ec6becf08bc6b8aa/llvm/include/llvm/Demangle/Utility.h#L50 [3]: https://github.com/llvm/llvm-project/blob/d7e631c7cd6d9c13b9519991ec6becf08bc6b8aa/llvm/include/llvm/Demangle/Demangle.h#L92-L93 [4]: https://gcc.gnu.org/onlinedocs/libstdc++/libstdc++-html-USERS-4.3/a01696.html
GeorgeARM
pushed a commit
to GeorgeARM/llvm-project
that referenced
this pull request
May 7, 2025
Currently the backing buffer of a `std::vector<char>` is passed[1] to `Demangler.getFunctionBaseName`. However, deeply inside the call stack `OutputBuffer::grow` will call[2] `std::realloc` if it needs to grow the buffer, leading to UB. The demangler APIs specify[3] that "`Buf` and `N` behave like the second and third parameters to `__cxa_demangle`" and the docs for the latter say[4] that the output buffer must be allocated with `malloc` (but can also be `NULL` and will then be realloced accordingly). Note: PR llvm#135863 changed this from a stack array to a `std::vector` and increased the size to 65K, but this can still lead to a crash if the demangled name is longer than that - yes, I'm surprised that a >65K-long function name happens in practice... [1]: https://github.com/llvm/llvm-project/blob/d7e631c7cd6d9c13b9519991ec6becf08bc6b8aa/llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp#L744 [2]: https://github.com/llvm/llvm-project/blob/d7e631c7cd6d9c13b9519991ec6becf08bc6b8aa/llvm/include/llvm/Demangle/Utility.h#L50 [3]: https://github.com/llvm/llvm-project/blob/d7e631c7cd6d9c13b9519991ec6becf08bc6b8aa/llvm/include/llvm/Demangle/Demangle.h#L92-L93 [4]: https://gcc.gnu.org/onlinedocs/libstdc++/libstdc++-html-USERS-4.3/a01696.html
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The function base name could be way long which overflows and leads to a crash. Update to extend the max size.
Also changed to use heap allocation(
std::vector<char>) to avoid stack overflow.