[Bug 2049897] Re: libdfp: FTBFS with glibc 2.39 snapshot

[Simon Chopin]

My initial suspect was 5c37d2065286d3db7b974266a3002bb5747d2e5d
(vfprintf-internal: Get rid of alloca.) in glibc. However, carefully
reading through the code I couldn't find anything fundamentally wrong
with the new code. Worse, I'm still unable to reproduce as standalone C
code.

However, something interesting happened: it works fine when compiling
the library using -O0. This could mean that the libdfp code is invoking
some UB somewhere.

Still working on it.

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https://bugs.launchpad.net/bugs/2049897

Title:
  libdfp: FTBFS with glibc 2.39 snapshot

Status in glibc package in Ubuntu:
  In Progress
Status in libdfp package in Ubuntu:
  New

Bug description:
  During the recent test rebuilds, one of the rebuild configurations was
  against a snapshot of the upcoming glibc 2.39.

  libdfp failed to build in that configuration with the error.

  Segmentation fault (core dumped)

  This has been confirmed locally with a more recent snapshot.

  See https://launchpad.net/ubuntu/+archive/test-rebuild-20231215-noble-
  glibc/+build/27491681/+files/buildlog_ubuntu-noble-
  amd64.libdfp_1.0.16-1_BUILDING.txt.gz for full logs,
  https://people.canonical.com/~ginggs/ftbfs-report/test-
  rebuild-20231215-noble-glibc-noble.html for the glibc rebuild report,
  and https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/glibc
  for the most recent glibc snapshot.

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