GNU C library 2.33 released

Nope, this is real. march=... does not (reliably? at all) affect the ISA stamping done by sysdeps/x86/isa-level.c, leading to e.g. 32-bit glibcs being built on fast machines for execution on old slow machines being stamped as requiring whatever fast x86-64 box you did your builds on, even if it was built with -march=i586 or something. (ld.so validates this using the CPUID and has no way to override the validation, so everything seems to work when you test it on your build host, even if you test in a VM, and then fails disastrously when you install it on the target machine, with every binary failing to run, even though they would all run just fine if only ld.so let them).

See this thread: https://sourceware.org/pipermail/libc-alpha/2021-February... (HJ's initial patch is definitely not sufficient).

For now, it's safest to turn off ISA stamping if you're building on one machine for execution on any machine which might be older (or otherwise of a lower ISA level). Of course there is no configure flag for this: you have to override the cache variable by adding libc_cv_include_x86_isa_level=no to your configure line.