x86: Alias memset to __builtin_memset.
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Message ID 20200326123841.134068-1-courbet@google.com
State Superseded
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  • x86: Alias memset to __builtin_memset.
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Commit Message

Clement Courbet March 26, 2020, 12:38 p.m. UTC
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:

Comments

Michael Ellerman March 27, 2020, 4:06 a.m. UTC | #1
Clement Courbet <courbet@google.com> writes:
> 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 ?

If it works then it looks like a much better fix than using -ffreestanding.

Please submit a patch with a change log etc. and I'd be happy to merge
it.

cheers
Segher Boessenkool March 27, 2020, 5:12 p.m. UTC | #2
Hi!

On Thu, Mar 26, 2020 at 01:38:39PM +0100, Clement Courbet wrote:
> --- 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 ?

Pedantically, jmp_buf should be an array type.  But, this will probably
work fine, and it certainly is better than what we had before.

You could do
  typedef long jmp_buf[JMP_BUF_LEN];
perhaps?

Thanks,


Segher

Patch
diff mbox series

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 ?