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Date: Thu, 16 Apr 2020 14:44:51 -0400
From: Rich Felker <dalias@libc.org>
To: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Subject: Re: [musl] Powerpc Linux 'scv' system call ABI proposal take 2
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On Thu, Apr 16, 2020 at 02:31:51PM -0400, Rich Felker wrote:
> > While on musl:
> > 
> > 0000000000000000 <kill>:
> >    0:	48 83 ec 08          	sub    $0x8,%rsp
> >    4:	48 63 ff             	movslq %edi,%rdi
> >    7:	48 63 f6             	movslq %esi,%rsi
> >    a:	b8 3e 00 00 00       	mov    $0x3e,%eax
> >    f:	0f 05                	syscall 
> >   11:	48 89 c7             	mov    %rax,%rdi
> >   14:	e8 00 00 00 00       	callq  19 <kill+0x19>
> >   19:	5a                   	pop    %rdx
> >   1a:	c3                   	retq   
> 
> Wow that's some extraordinarily bad codegen going on by gcc... The
> sign-extension is semantically needed and I don't see a good way
> around it (glibc's asm is kinda a hack taking advantage of kernel not
> looking at high bits, I think), but the gratuitous stack adjustment
> and refusal to generate a tail call isn't. I'll see if we can track
> down what's going on and get it fixed.

It seems to be https://gcc.gnu.org/bugzilla/show_bug.cgi?id=14441
which I've updated with a comment about the above.

Rich