release/18.x: [libcxx] Align __recommend() + 1 by __endian_factor (#90292)
#95264
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@ldionne @philnik777 What do you think about merging this PR to the release branch? |
llvmbot
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@llvm/pr-subscribers-libcxx Author: None (llvmbot) ChangesRequested by: @DimitryAndric Full diff: https://github.com/llvm/llvm-project/pull/95264.diff 1 Files Affected:
diff --git a/libcxx/include/string b/libcxx/include/string
index ba169c3dbfc9e..56e2ef09947f4 100644
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -1943,10 +1943,10 @@ private:
if (__s < __min_cap) {
return static_cast<size_type>(__min_cap) - 1;
}
- size_type __guess =
- __align_it < sizeof(value_type) < __alignment ? __alignment / sizeof(value_type) : 1 > (__s + 1) - 1;
+ const size_type __boundary = sizeof(value_type) < __alignment ? __alignment / sizeof(value_type) : __endian_factor;
+ size_type __guess = __align_it<__boundary>(__s + 1) - 1;
if (__guess == __min_cap)
- ++__guess;
+ __guess += __endian_factor;
return __guess;
}
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Approved per discussion in #90292. @vitalybuka It would be amazing if you could run this PR through the same tests that made you find the bug that you fixed with #90292 |
Looking, I will approve after validation. |
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release/18.x https://lab.llvm.org/buildbot/#/builders/168/builds/20916 OK Problem is that release/18.x suppose to fail, but it does not fail, because sized new/delete is OFF there. So: release/18.x+#90373 https://lab.llvm.org/buildbot/#/builders/168/builds/20919 BAD LGTM |
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Do we need to merge this manually? GitHub's UI does not allow to merge the PR. :) |
I expect this requires by @tstellar (the release manager). |
) Previously, there was a ternary conditional with a less-than comparison appearing inside a template argument, which was really confusing because of the <...> of the function template. This patch rewrites the same statement on two lines for clarity. (cherry picked from commit 382f70a)
This is detected by asan after llvm#83774 Allocation size will be divided by `__endian_factor` before storing. If it's not aligned, we will not be able to recover allocation size to pass into `__alloc_traits::deallocate`. we have code like this ``` auto __allocation = std::__allocate_at_least(__alloc(), __recommend(__sz) + 1); __p = __allocation.ptr; __set_long_cap(__allocation.count); void __set_long_cap(size_type __s) _NOEXCEPT { __r_.first().__l.__cap_ = __s / __endian_factor; __r_.first().__l.__is_long_ = true; } size_type __get_long_cap() const _NOEXCEPT { return __r_.first().__l.__cap_ * __endian_factor; } inline ~basic_string() { __annotate_delete(); if (__is_long()) __alloc_traits::deallocate(__alloc(), __get_long_pointer(), __get_long_cap()); } ``` 1. __recommend() -> even size 2. `std::__allocate_at_least(__alloc(), __recommend(__sz) + 1)` - > not even size 3. ` __set_long_cap() `- > lose one bit of size for __endian_factor == 2 (see `/ __endian_factor`) 4. `__alloc_traits::deallocate(__alloc(), __get_long_pointer(), __get_long_cap())` -> uses even size (see `__get_long_cap`) (cherry picked from commit d129ea8)
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Could someone write a release note for this? |
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This appears to blow up compilation on the Pi3 for certain source files on FreeBSD 14.1 with a SEGV in 'AArch64O0PreLegalizerCombiner'. Specifically I have filed this bug thread for FreeBSD: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=280038 I have bisected the source and reverting this commit resolves the crash. I have a reproducing source file that is only ~400 lines with it being nearly all OpenSSL calls -- and in an attempt to further isolate it, as the FreeBSD bugtracker will not take the reproducer file (too large) as that source file was already split off and very small I took individual functions out into their own source files -- and got it to dump on two of them but not consistently; often, if I simply re-type "make" it would complete the second time! The blow-up only happens with this commit in, and only on the Pi3 -- and I have used both a very old one (no HAT header for POE, for example) and a brand new unit (has the header) with identical results, so a specific hardware fault is excluded. The same boot media inserted into a Pi4 and booted compiles the code without complaint. Further, the same code, on the same revision of OS and clang/llvm but built and running on an AMD64 system with the commit in also builds without complaint. The reproducer files are still too large to upload into FreeBSD's bugtracker, but since I now have a routine that is ~100 lines that does reproduce it, I simply posted that function's source. |
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@tickerguy Thanks for the heads up. @tstellar I read the thread in the linked FreeBSD tracker up to |
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Its definitely architecture-specific. The media in question where I first saw this will boot and run on both a Pi3 and Pi4 but on the "4" it never blows up, whether via the original "make" or if I execute the reproducer shell script after it blows on the "3", I shut it down, stick the same card in the "4", boot it and then run the reproducer script. If I take the reproducer over to my much-larger AMD64 build system it completes every time as well. On the "3" it does blow up, and not just there -- although its intermittent now that I've broken out the routines in the one file that was crashing reliably into three. This started when those routines, all of which are heavy with OpenSSL function calls (and little else; they perform AES encryption, decryption, and MAC computation) were part of a much larger file and it failed reliably in those routines; I split them out in an attempt to isolate the problem. Obviously separating a function call from one file with a lot of functions into its own separate ".c" file shouldn't change anything but now it crashes a good part of the time - but not every time - in that if I run the reproducer script it will will crash perhaps half or 3/4 of the time -- but the other times completes and produces the expected .o file. That its intermittent is even worse, obviously, since you'd expect a compilation of the same file on the same CPU to act in a reasonably-deterministic fashion. |
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@tickerguy From the bugzilla thread, do I understand correctly that the last good version of clang was 18.1.6 ? |
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Reverting the one commit (three lines) fixes it on the Pi3 and does not break it on any of the other architectures I have. releng/14.1 does not have that commit in it, which is why I never saw it until I built on stable/14, which does. I thought it was elsewhere as there are other commits to llvm but bisection narrowed the blow-up down to this which is why I commented on this thread here specifically. Of note I built the stable/14 media for the Pis on my AMD64 system that is running stable/14 and thus has this commit in it -- and it has no negative impact on that architecture (and of course a full OS build does a lot of compiling) which reinforces that the problem is architecture-specific. With that out it does not blow up but when it comes to why I lack sufficient understanding of the impacted code to know |
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My thread over on FreeBSD's bugtracker has more context after plenty of additional attempts to isolate this; specifically, simply changing whether or not assertions are enabled in llvm and a couple other places, or turning on debug file building,, even though such output files are not then in use when compilation is done, makes it disappear. This looks like a rather obscure problem somewhere related specifically to the Pi3's CPU architecture (likely not the llvm project itself) but without being able to include symbols and such (I can get a backtrace from lldb when it happens but without symbols its machine code without much context) figuring out exactly why it occurs is looking rather problematic. |
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I have now marked this OBE over on FreeBSD; it disappeared in 14.2 and no longer manifests, although exactly which commit resolved it in their tree is not clear. |
Backport 382f70a d129ea8
Requested by: @DimitryAndric