SIGILL with new libc qsort_r implementation in BranchFolder::MergePotentialsElt #71312
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@llvm/issue-subscribers-libc Author: Cristian Rodríguez (crrodriguez)
https://github.com/llvm/llvm-project/blob/7c1ad51e018c5a1517ca6fb58a4d7027a8bec64e/llvm/lib/CodeGen/BranchFolding.cpp#L491
Now glibc compares an object with itself, just like when _GLIBCXX_DEBUG is enabled therefore explicit unreachable triggers. this breaks at least any rustc compiler available. |
nikic
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`MergePotentialElts::operator<` asserts that the two elements being compared are not equal. However, sorting functions are allowed to invoke the comparison function with equal arguments (though they usually don't for efficiency reasons). There is an existing special-case that disables the assert if _GLIBCXX_DEBUG is used, which may invoke the comparator with equal args to verify strict weak ordering. I believe libc++ also has strict weak ordering checks under some options nowadays. Most recently llvm#71312 was reported, where a change to glibc's qsort_r implementation can also result in comparison between equal elements. From what I understood this is an inefficiency that will be fixed on the glibc side as well, but I think at this point we should just remove this assertion. Fixes llvm#71312.
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/cherry-pick 74a76a2 |
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/branch llvm/llvm-project-release-prs/issue71312 |
llvmbot
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`MergePotentialElts::operator<` asserts that the two elements being compared are not equal. However, sorting functions are allowed to invoke the comparison function with equal arguments (though they usually don't for efficiency reasons). There is an existing special-case that disables the assert if _GLIBCXX_DEBUG is used, which may invoke the comparator with equal args to verify strict weak ordering. I believe libc++ also has strict weak ordering checks under some options nowadays. Recently, #71312 was reported, where a change to glibc's qsort_r implementation can also result in comparison between equal elements. From what I understood, this is an inefficiency that will be fixed on the glibc side as well, but I think at this point we should just remove this assertion. Fixes llvm/llvm-project#71312. (cherry picked from commit 74a76a288562c486f377121855ef7db0386e0e43)
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/pull-request llvm/llvm-project-release-prs#771 |
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Pull request is still open. |
tru
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Nov 14, 2023
`MergePotentialElts::operator<` asserts that the two elements being compared are not equal. However, sorting functions are allowed to invoke the comparison function with equal arguments (though they usually don't for efficiency reasons). There is an existing special-case that disables the assert if _GLIBCXX_DEBUG is used, which may invoke the comparator with equal args to verify strict weak ordering. I believe libc++ also has strict weak ordering checks under some options nowadays. Recently, #71312 was reported, where a change to glibc's qsort_r implementation can also result in comparison between equal elements. From what I understood, this is an inefficiency that will be fixed on the glibc side as well, but I think at this point we should just remove this assertion. Fixes llvm/llvm-project#71312. (cherry picked from commit 74a76a288562c486f377121855ef7db0386e0e43)
qihangkong
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Apr 18, 2024
`MergePotentialElts::operator<` asserts that the two elements being compared are not equal. However, sorting functions are allowed to invoke the comparison function with equal arguments (though they usually don't for efficiency reasons). There is an existing special-case that disables the assert if _GLIBCXX_DEBUG is used, which may invoke the comparator with equal args to verify strict weak ordering. I believe libc++ also has strict weak ordering checks under some options nowadays. Recently, #71312 was reported, where a change to glibc's qsort_r implementation can also result in comparison between equal elements. From what I understood, this is an inefficiency that will be fixed on the glibc side as well, but I think at this point we should just remove this assertion. Fixes llvm/llvm-project#71312.
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llvm-project/llvm/lib/CodeGen/BranchFolding.cpp
Line 491 in 7c1ad51
Now glibc compares an object with itself, just like when _GLIBCXX_DEBUG is enabled therefore explicit unreachable triggers. this breaks at least any rustc compiler available.
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