This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [PATCH] PR target/66232: -fPIC -fno-plt -mx32 fails to generate indirect branch via GOT
- From: Alexander Monakov <amonakov at ispras dot ru>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: Richard Henderson <rth at redhat dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>, Uros Bizjak <ubizjak at gmail dot com>
- Date: Thu, 21 May 2015 22:32:39 +0300 (MSK)
- Subject: Re: [PATCH] PR target/66232: -fPIC -fno-plt -mx32 fails to generate indirect branch via GOT
- Authentication-results: sourceware.org; auth=none
- References: <20150521125904 dot GA26391 at gmail dot com> <555E26F3 dot 3020202 at redhat dot com> <CAMe9rOr+hE_3W2AfXbZH0DziC-z6LA5xtx5OGNy40V5Df-9gRg at mail dot gmail dot com> <555E2CB8 dot 3040603 at redhat dot com> <CAMe9rOrD-VCAGSNs2D5h4+zn+LRmVO05cOjbj9By1-+Xy++BEQ at mail dot gmail dot com>
On Thu, 21 May 2015, H.J. Lu wrote:
> On Thu, May 21, 2015 at 12:06 PM, Richard Henderson <rth@redhat.com> wrote:
> > On 05/21/2015 12:01 PM, H.J. Lu wrote:
> >> +++ b/gcc/testsuite/gcc.target/i386/pr66232-1.c
> >> @@ -0,0 +1,13 @@
> >> +/* { dg-do compile { target *-*-linux* } } */
> >> +/* { dg-options "-O2 -fpic -fno-plt" } */
> >> +
> >> +extern void bar (void);
> >> +
> >> +void
> >> +foo (void)
> >> +{
> >> + bar ();
> >> +}
> >> +
> >> +/* { dg-final { scan-assembler "jmp\[ \t\]*.bar@GOTPCREL" { target { ! ia32 } } } } */
> >> +/* { dg-final { scan-assembler "call\[ \t\]*.bar@GOT\\(" { target ia32 } } } */
> >
> > Do you really want to check for no tail call for ia32 here?
> > That's really just a missed optimization, surely.
> >
> >
>
> I'd like to keep it. When it is fixed, we can update it. I tried:
>
> https://gcc.gnu.org/ml/gcc-patches/2015-05/msg00230.html
>
> and got
>
> call __x86.get_pc_thunk.ax
> addl $_GLOBAL_OFFSET_TABLE_, %eax
> subl $28, %esp
> .cfi_def_cfa_offset 32
> movl bar@GOT(%eax), %eax
> movl %eax, 12(%esp)
> addl $28, %esp
> .cfi_def_cfa_offset 4
> jmp *%eax
>
> This is very odd code, comparing against
To avoid that, you need the CLOBBERED_REGS patch too:
https://gcc.gnu.org/ml/gcc-patches/2015-05/msg00227.html
Alexander
> call __x86.get_pc_thunk.ax
> addl $_GLOBAL_OFFSET_TABLE_, %eax
> subl $12, %esp
> .cfi_def_cfa_offset 16
> call *bar@GOT(%eax)
> addl $12, %esp
> .cfi_def_cfa_offset 4
> ret