On Wed, Mar 23, 2022 at 11:29:48PM +0100, Guillem Jover wrote: >... > What unearthed this was a recentish glibc upload that AFAIR has started > merging its libpthread library into libc proper, and added a new symbol > for a variable (__libc_single_threaded@GLIBC_2.32).
The merging only happens in 2.34 (currently in experimental), but this new way of detecting multithreading was added in 2.32. > I guess the archive should be checked for other instances of at least > that glibc issue, because that can affect partial upgrades in a pretty > nasty way (with programs being unable to be run-time linked). So that > would imply any program that has been: > > * built against glibc >= 2.32-0experimental0 > * built using binutils >= 2.26 > * built using dpkg-dev < 1.21.0 FTR, this seems to be a 2 month window (give or take a few days due to buildd chroots being updated only twice per week): https://tracker.debian.org/news/1255840/accepted-glibc-232-1-source-into-unstable/ https://tracker.debian.org/news/1284072/accepted-dpkg-1210-source-into-unstable/ > * containing a copy reloc for __libc_single_threaded: > objdump -R $prog | grep 'R_[^ ]*_COPY .* __libc_single_threaded' > > Most of this information should be available at least from the .buildinfo > files. Relevant is also that the binary packages do not already have dependencies on libc6 >= 2.32 for other reasons. >... > This could have affected other programs using other versioned variables > from other shared libraries, for quite some time, but not that many shared > libraries use versioned symbols, but checking that would imply more effort > to detect. :/ Versioned symbols are common, but: >... > So this involves shared libraries using versioned symbols, for symbols > that are objects (variables instead of functions or methods), >... Global variables as part of a library API are usually considered bad practice, and then you'd need a case where such a new variable is used but no new function. __libc_single_threaded is special, and looking at cppcheck the problem occurs in practice mainly due to libstdc++ using it for atomics in its headers when available. > Thanks, > Guillem cu Adrian
