Re: [PATCH] x86: Properly handle IFUNC function pointer reference

["H.J. Lu" <hjl.tools@gmail.com>]

On Tue, May 31, 2022 at 3:47 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> Update
>
> commit 68c4956b1401de70173848a6bdf620cb42fa9358
> Author: H.J. Lu <hjl.tools@gmail.com>
> Date:   Tue Apr 26 09:08:54 2022 -0700
>
>     x86: Properly handle function pointer reference
>
> to properly handle IFUNC function pointer reference.  Since IFUNC symbol
> value is only known at run-time, set pointer_equality_needed for IFUNC
> function pointer reference in PDE so that it will be resolved to its PLT
> entry directly.
>
> bfd/
>
>         PR ld/29216
>         * elf32-i386.c (elf_i386_scan_relocs): Set pointer_equality_needed
>         for IFUNC function pointer reference in PDE.
>         * elf64-x86-64.c (elf_x86_64_scan_relocs): Likewise.
>
> ld/
>
>         PR ld/29216
>         * testsuite/ld-ifunc/ifunc.exp: Run PR ld/29216 test.
>         * testsuite/ld-ifunc/pr29216.c: New file.
> ---
>  bfd/elf32-i386.c                |  8 ++++-
>  bfd/elf64-x86-64.c              |  8 ++++-
>  ld/testsuite/ld-ifunc/ifunc.exp |  9 +++++
>  ld/testsuite/ld-ifunc/pr29216.c | 62 +++++++++++++++++++++++++++++++++
>  4 files changed, 85 insertions(+), 2 deletions(-)
>  create mode 100644 ld/testsuite/ld-ifunc/pr29216.c
>
> diff --git a/bfd/elf32-i386.c b/bfd/elf32-i386.c
> index b034154fb97..3bc710096aa 100644
> --- a/bfd/elf32-i386.c
> +++ b/bfd/elf32-i386.c
> @@ -1778,7 +1778,13 @@ elf_i386_scan_relocs (bfd *abfd,
>                   if (r_type == R_386_32
>                       && (sec->flags & SEC_READONLY) == 0)
>                     func_pointer_ref = true;
> -                 else
> +
> +                 /* IFUNC symbol needs pointer equality in PDE so that
> +                    function pointer reference will be resolved to its
> +                    PLT entry directly.  */
> +                 if (!func_pointer_ref
> +                     || (bfd_link_pde (info)
> +                         && h->type == STT_GNU_IFUNC))
>                     h->pointer_equality_needed = 1;
>                 }
>
> diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
> index 6d69d6141ee..eac5e83d7f1 100644
> --- a/bfd/elf64-x86-64.c
> +++ b/bfd/elf64-x86-64.c
> @@ -2221,7 +2221,13 @@ elf_x86_64_scan_relocs (bfd *abfd, struct bfd_link_info *info,
>                               && (r_type == R_X86_64_32
>                                   || r_type == R_X86_64_32S))))
>                     func_pointer_ref = true;
> -                 else
> +
> +                 /* IFUNC symbol needs pointer equality in PDE so that
> +                    function pointer reference will be resolved to its
> +                    PLT entry directly.  */
> +                 if (!func_pointer_ref
> +                     || (bfd_link_pde (info)
> +                         && h->type == STT_GNU_IFUNC))
>                     h->pointer_equality_needed = 1;
>                 }
>
> diff --git a/ld/testsuite/ld-ifunc/ifunc.exp b/ld/testsuite/ld-ifunc/ifunc.exp
> index 1cd8d388b26..fdb65d01f9f 100644
> --- a/ld/testsuite/ld-ifunc/ifunc.exp
> +++ b/ld/testsuite/ld-ifunc/ifunc.exp
> @@ -714,6 +714,15 @@ run_ld_link_exec_tests [list \
>         "pr18841cn" \
>         "pr18841.out" \
>      ] \
> +    [list \
> +       "Run pr29216" \
> +       "$NOPIE_LDFLAGS" \
> +       "" \
> +       { pr29216.c } \
> +       "pr29216" \
> +       "pass.out" \
> +       "-fPIC" \
> +    ] \
>  ]
>
>  # The pr23169 testcase is not valid.  In general, you can't call ifunc
> diff --git a/ld/testsuite/ld-ifunc/pr29216.c b/ld/testsuite/ld-ifunc/pr29216.c
> new file mode 100644
> index 00000000000..5019c723c2b
> --- /dev/null
> +++ b/ld/testsuite/ld-ifunc/pr29216.c
> @@ -0,0 +1,62 @@
> +#include <stdio.h>
> +
> +static int
> +one (void)
> +{
> +  return -30;
> +}
> +
> +int foo (void) __attribute__ ((ifunc ("resolve_foo")));
> +
> +void *
> +resolve_foo (void)
> +{
> +  return (void *) one;
> +}
> +
> +typedef int (*foo_p) (void);
> +
> +foo_p foo_ptr = foo;
> +
> +foo_p
> +__attribute__ ((noinline))
> +get_foo_p (void)
> +{
> +  return foo_ptr;
> +}
> +
> +foo_p
> +__attribute__ ((noinline))
> +get_foo (void)
> +{
> +  return foo;
> +}
> +
> +int
> +main (void)
> +{
> +  foo_p p;
> +
> +  p = get_foo ();
> +  if (p != foo)
> +    __builtin_abort ();
> +  if ((*p) () != -30)
> +    __builtin_abort ();
> +
> +  p = get_foo_p ();
> +  if (p != foo)
> +    __builtin_abort ();
> +  if ((*p) () != -30)
> +    __builtin_abort ();
> +
> +  if (foo_ptr != foo)
> +    __builtin_abort ();
> +  if ((*foo_ptr) () != -30)
> +    __builtin_abort ();
> +  if (foo () != -30)
> +    __builtin_abort ();
> +
> +  printf ("PASS\n");
> +
> +  return 0;
> +}
> --
> 2.36.1
>

I am backporting this to 2.38 branch.

-- 
H.J.