Linux build: fix noreturn and silence spurious falls through objtools warnings
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Objtool correctly complains that `spl_panic()` and `luaD_throw()` are missing an `atribute((noreturn))` annotation. They were in place but removed in a previous commit to work around spurious objtool warnings they caused. Add them back in, the spurious warnings are addressed in a separate commit. Signed-off-by: Attila Fülöp <[email protected]>
If we correctly annotate noreturn functions we end up with a ton of spurious `falls through to next function` objtool warnings during the build. Silence them by skipping objtools unreachable checks. Please note that this will skip the noreturn checks as well. The proper fix would be to ask the objtool maintainers to add our noreturn functions to their `noretuns.h` header file. Signed-off-by: Attila Fülöp <[email protected]>
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This is like fighting Hydra. |
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I'm at a loss. This works perfectly fine with the standard ArchLinux 6.14 kernel. It somewhat works with Fedora but creates a new set of warnings. On Debian/Ubuntu/Alma it completely fails to silence the falls through warnings, although in theory, it should work with kernels >= 5.13. |
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Seems to need Linux 6.14., older versions still warn. The flag exists since 4.14 but won't silence the warning. |
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Motivation and Context
Follow-up for #17410
Objtool correctly complains that
spl_panic()andluaD_throw()are missing anattribute((noreturn))annotation. Unfortunately, adding the attribute results in a ton of spuriousfalls through to next functionwarnings. This is documented [1], so I patchedobjtoolto includespl_panic()andluaD_throw()in the globalnoreturnfunctions list [2] and indeed all spl related (see below) warnings are gone.Description
Getting the
objtoolmaintainer to add our functions to this list isn't likely to be a viable path. Therefore I took a differnet approach and silenced them via the--no-unreachableobjtoolflag, they were false positives anyway. The first commit leaves us withlua{,L}_error()noreturnwarnings which are also silenced by the second commit. Obviously they should be fixed as well, but I'd rather prefer to do this in a subsequent PR since it's a bit more involved (changing function return types).[1] https://github.com/torvalds/linux/blob/7a912d04415b372324e5a8dfad3360d993d0c23a/tools/objtool/Documentation/objtool.txt#L388-L399
[2] https://github.com/torvalds/linux/blob/v6.15/tools/objtool/noreturns.h
https://github.com/torvalds/linux/blob/7a912d04415b372324e5a8dfad3360d993d0c23a/tools/objtool/check.c#L255-L257
How Has This Been Tested?
Build locally and verified that no
objtoolwarnings are left.Types of changes
Checklist:
Signed-off-by.