Messages in this thread | | | From | Nick Desaulniers <> | Date | Thu, 26 Mar 2020 10:18:45 -0700 | Subject | Re: [PATCH] x86: Alias memset to __builtin_memset. |
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On Thu, Mar 26, 2020 at 5:38 AM Clement Courbet <courbet@google.com> wrote: > > I discussed with the original authors who added freestanding to our > build. It turns out that it was added globally but this was just to > to workaround powerpc not compiling under clang, but they felt the > fix was appropriate globally. > > Now Nick has dug up https://lkml.org/lkml/2019/8/29/1300, which > advises against freestanding. Also, I've did some research and > discovered that the original reason for using freestanding for > powerpc has been fixed here: > https://lore.kernel.org/linuxppc-dev/20191119045712.39633-3-natechancellor@gmail.com/ > > I'm going to remove -ffreestanding from downstream, so we don't really need > this anymore, sorry for waisting people's time. > > I wonder if the freestanding fix from the aforementioned patch is really needed > though. I think that clang is actually right to point out the issue. > I don't see any reason why setjmp()/longjmp() are declared as taking longs > rather than ints. The implementation looks like it only ever propagates the > value (in longjmp) or sets it to 1 (in setjmp), and we only ever call longjmp > with integer parameters. But I'm not a PowerPC expert, so I might > be misreading the code. > > > So it seems that we could just remove freestanding altogether and rewrite the > code to: > > diff --git a/arch/powerpc/include/asm/setjmp.h b/arch/powerpc/include/asm/setjmp.h > index 279d03a1eec6..7941ae68fe21 100644 > --- a/arch/powerpc/include/asm/setjmp.h > +++ b/arch/powerpc/include/asm/setjmp.h > @@ -12,7 +12,9 @@ > > #define JMP_BUF_LEN 23 > -extern long setjmp(long *); > -extern void longjmp(long *, long); > +typedef long * jmp_buf; > + > +extern int setjmp(jmp_buf); > +extern void longjmp(jmp_buf, int); > > I'm happy to send a patch for this, and get rid of more -ffreestanding. > Opinions ?
Yes, I think the above diff and additionally cleaning up -ffreestanding from arch/powerpc/kernel/Makefile and arch/powerpc/xmon/Makefile would be a much better approach. If that's good enough to fix the warning, I kind of can't believe we didn't spot that in the original code review!
Actually, the god awful warning was: ./arch/powerpc/include/asm/setjmp.h:10:13: error: declaration of built-in function 'setjmp' requires the declaration of the 'jmp_buf' type, commonly provided in the header <setjmp.h>. [-Werror,-Wincomplete-setjmp-declaration] extern long setjmp(long *) __attribute__((returns_twice)); ^ So jmp_buf was missing, wasn't used, but also the long vs int confusion.
I tested the above diff, all calls to setjmp under arch/powerpc/ just compare the return value against 0. Callers of longjmp just pass 1 for the final parameter. So the above changes should be no functional change. -- Thanks, ~Nick Desaulniers
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