Source: mbuffer Version: 20260511+ds1-2 Severity: important Tags: ftbfs
Hi, I am recording a longstanding build/test failure observed on Debian GNU/Hurd (hurd-i386). This identifies where the failure has been observed; it does not establish that the problem is specific to Hurd. The affected synchronization code is shared between platforms, and the root cause and broader platform impact have not yet been established. The 20260511+ds1-2 build on ironforge.sceen.net completes compilation and linking, and test0 passes. During the build-time test suite, test1 runs: ./mbuffer -i test.tar -f -o test1.tar -o /dev/null -H Here test.tar is generated by the upstream test suite and -H selects MD5. The expected result is successful completion of both outputs and the hash calculation, followed by the test's checksum comparison. Instead, mbuffer aborts during the transfer: mbuffer: mbuffer.c:366: syncSenders: Assertion `(buf != 0) || Terminate' failed. make[1]: *** [Makefile:123: test1] Aborted (core dumped) dh_auto_test: error: make -j1 check TESTSUITEFLAGS="-j1 --verbose" VERBOSE=1 returned exit code 2 make: *** [debian/rules:28: binary-arch] Error 255 Full build log (29 September 2026): https://buildd.debian.org/status/fetch.php?pkg=mbuffer&arch=hurd-i386&ver=20260511%2Bds1-2&stamp=1790649819&raw=0 Selected environment details, taken from that log: Build/host/machine architecture: hurd-i386 sbuild: 0.89.3 gcc-16: 16.2.0-2 libc0.3: 2.43-7~hurd.1 libgcrypt20: 1.12.4-2 This failure predates the adoption upload. The same test and assertion also fail in these older hurd-i386 build logs: 20260511+ds1-1, 9 July 2026 (mbuffer.c:366): https://buildd.debian.org/status/fetch.php?pkg=mbuffer&arch=hurd-i386&ver=20260511%2Bds1-1&stamp=1783641146&raw=0 20230301+ds1-1, 3 March 2023 (mbuffer.c:356): https://buildd.debian.org/status/fetch.php?pkg=mbuffer&arch=hurd-i386&ver=20230301%2Bds1-1&stamp=1677833430&raw=0 This establishes that the symptom is longstanding, not which version introduced it. The -2 adoption changes do not alter upstream code, the Debian patch queue, build rules or test1. One possible lead from static inspection is the reusable synchronization barrier in syncSenders(): it calls pthread_cond_wait() once, without rechecking a predicate or generation on return. POSIX permits spurious wakeups, so a successful return alone does not establish that a new buffer has been published. This is a hypothesis for investigation, not a confirmed explanation of the buildd failure: https://pubs.opengroup.org/onlinepubs/9799919799/functions/pthread_cond_wait.html The function is unchanged in upstream 20260926, but I have not tested that release on Hurd and cannot infer its runtime result from this comparison. This report is based on the public native build logs and source inspection. I do not currently have a local Hurd test environment and have not reproduced the failure locally. No validated fix is available yet. Help with reproducing the failure and narrowing down the cause would be welcome. Best regards, Federico Molara <[email protected]>
