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buffer flush issue on glibc FILE #4229

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emmanuelthome opened this issue Nov 7, 2024 · 1 comment
Closed

buffer flush issue on glibc FILE #4229

emmanuelthome opened this issue Nov 7, 2024 · 1 comment

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@emmanuelthome
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Hi

The following code produces wrong output on the current master (720da57): https://godbolt.org/z/x53n1KhcM. I tried g++-14, clang-16, clang-20. Linux current debian testing, glibc 2.40-3 (this happens on the current debian:testing docker image)

When the underlying FILE gets flushed, there's data from the existing buffer that gets printed again. E.g. the output is:

$ clang++ -I include  mytest.cpp src/format.cc src/os.cc && ./a.out
5393 defgh493

The problem disappears if I set FMT_USE_FALLBACK_FILE to 1.
@vitaut
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vitaut commented Nov 9, 2024

Fixed in a35389b, thanks for reporting.

@vitaut vitaut closed this as completed Nov 9, 2024
emmanuelthome added a commit to cado-nfs/cado-nfs that referenced this issue Jan 6, 2025
@emmanuelthome
revert upstream fmt commit 439b6d72
ac11ce2 
Clearly fmt 11.0.2 does not compile with clang-20. Yet the current fmt
tip-of-tree triggers a bug with the full_F7 test, where apparently the
fflush(_unlocked) seems to leave garbage in the write buffer. See
fmtlib/fmt#4229 for a reproducer
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@vitaut @emmanuelthome