Messages in this thread | | | Date | Sat, 26 Mar 2022 13:00:08 -0700 | From | Nathan Chancellor <> | Subject | Re: [PATCH] um: Fix filtering '-mno-global-merge' |
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On Sat, Mar 26, 2022 at 12:29:55PM +0900, Masahiro Yamada wrote: > On Wed, Mar 23, 2022 at 2:39 AM Nathan Chancellor <nathan@kernel.org> wrote: > > > > When booting a clang compiled UML kernel, the kernel panics when trying > > to run init: > > > > wait_stub_done : failed to wait for SIGTRAP, pid = 651294, n = 651294, errno = 0, status = 0xb7f > > Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b > > > > After the commit in Fixes, many flags from KBUILD_CFLAGS do not appear > > in USER_CFLAGS, likely due to USER_CFLAGS initially being a recursive > > variable ("VAR =") then being switched to a simple ("VAR :=") variable. > > For example, diffing arch/x86/um/.ptrace_user.o.cmd shows flags such as > > '-Os' and '-fno-delete-null-pointer-checks' getting dropped, which both > > impact code generation. > > > > Rework the filtering to use filter-out instead of patsubst, which allows > > all the patterns that USER_CFLAGS cares about to be excluded in one > > command and ensures all flags from KBUILD_CFLAGS are transferred over to > > USER_CFLAGS properly, which resolves the boot issue noted above. > > > > Fixes: 6580c5c18fb3 ("um: clang: Strip out -mno-global-merge from USER_CFLAGS") > > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > > > > Can we remove -mno-global-merge entirely? > > > 61163efae02040f66a95 was a very old commit, > without enough explanation. > > Shall we remove -mno-global-merge, and do compile-tests. > If we are hit by problems for arm/arm64, we can re-add it.
Yes, I think that was the conversation that we had on the commit that this fixes:
https://lore.kernel.org/r/YiD7R2wRxoWxtVq7@dev-arch.thelio-3990X/
I can test that on my Raspberry Pi 3 and 4 on Monday, although I would like for this patch to be picked up in the meantime so that it is possible to test UML on -next with clang. We can remove -mno-global-merge in a follow up change, if you do not have any objections?
Cheers, Nathano
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