[PATCH] i386: Load external function address via GOT slot

[Uros Bizjak]

On Tue, Jan 22, 2019 at 2:41 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> With noplt attribute, we load the external function address via the GOT
> slot so that linker won't create an PLT entry for extern function address.
>
> gcc/
>
>         PR target/88954
>         * config/i386/i386.c (ix86_force_load_from_GOT_p): Also check
>         noplt attribute.
>
> gcc/testsuite/
>
>         PR target/88954
>         * gcc.target/i386/pr88954-1.c: New test.
>         * gcc.target/i386/pr88954-2.c: Likewise.

LGTM.

Thanks,
Uros.

> ---
>  gcc/config/i386/i386.c                    |  6 +++++-
>  gcc/testsuite/gcc.target/i386/pr88954-1.c | 15 +++++++++++++++
>  gcc/testsuite/gcc.target/i386/pr88954-2.c | 16 ++++++++++++++++
>  3 files changed, 36 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/gcc.target/i386/pr88954-1.c
>  create mode 100644 gcc/testsuite/gcc.target/i386/pr88954-2.c
>
> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
> index 8abff99cc62..9ca5596c4af 100644
> --- a/gcc/config/i386/i386.c
> +++ b/gcc/config/i386/i386.c
> @@ -15189,10 +15189,14 @@ ix86_force_load_from_GOT_p (rtx x)
>  {
>    return ((TARGET_64BIT || HAVE_AS_IX86_GOT32X)
>           && !TARGET_PECOFF && !TARGET_MACHO
> -         && !flag_plt && !flag_pic
> +         && !flag_pic
>           && ix86_cmodel != CM_LARGE
>           && GET_CODE (x) == SYMBOL_REF
>           && SYMBOL_REF_FUNCTION_P (x)
> +         && (!flag_plt
> +             || (SYMBOL_REF_DECL (x)
> +                 && lookup_attribute ("noplt",
> +                                      DECL_ATTRIBUTES (SYMBOL_REF_DECL (x)))))
>           && !SYMBOL_REF_LOCAL_P (x));
>  }
>
> diff --git a/gcc/testsuite/gcc.target/i386/pr88954-1.c b/gcc/testsuite/gcc.target/i386/pr88954-1.c
> new file mode 100644
> index 00000000000..69cb940ae4f
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr88954-1.c
> @@ -0,0 +1,15 @@
> +/* { dg-do compile { target *-*-linux* } } */
> +/* { dg-options "-O2 -fno-pic -fplt" } */
> +
> +extern void bar (void) __attribute__((noplt));
> +
> +void *
> +foo (void)
> +{
> +  return &bar;
> +}
> +
> +/* { dg-final { scan-assembler "mov\(l|q\)\[ \t\]*bar@GOTPCREL" { target { ! ia32 } } } } */
> +/* { dg-final { scan-assembler "movl\[ \t\]*bar@GOT," { target { ia32 && got32x_reloc } } } } */
> +/* { dg-final { scan-assembler-not "\(mov|lea\)\(l|q\)\[ \t\]*\(\\\$|\)bar," { target { ! ia32 } } } } */
> +/* { dg-final { scan-assembler-not "\(mov|lea\)l\[ \t\]*\(\\\$|\)bar," { target { ia32 && got32x_reloc } } } } */
> diff --git a/gcc/testsuite/gcc.target/i386/pr88954-2.c b/gcc/testsuite/gcc.target/i386/pr88954-2.c
> new file mode 100644
> index 00000000000..3bc4ee47bae
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr88954-2.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile { target *-*-linux* } } */
> +/* { dg-options "-O2 -fno-pic -fplt" } */
> +
> +extern void bar (void) __attribute__((noplt));
> +extern void *p;
> +
> +void
> +foo (void)
> +{
> +  p = &bar;
> +}
> +
> +/* { dg-final { scan-assembler "mov\(l|q\)\[ \t\]*bar@GOTPCREL" { target { ! ia32 } } } } */
> +/* { dg-final { scan-assembler "movl\[ \t\]*bar@GOT," { target { ia32 && got32x_reloc } } } } */
> +/* { dg-final { scan-assembler-not "mov\(l|q\)\[ \t\]*\\\$bar," { target { ! ia32 } } } } */
> +/* { dg-final { scan-assembler-not "mov\(l|q\)\[ \t\]*\\\$bar," { target { ia32 && got32x_reloc } } } } */
> --
> 2.20.1
>