[Mesa-dev] [Mesa-stable] [PATCH] mapi: avoid text relocation in x86 tsd stubs

[Ian Romanick]

On 10/31/2018 09:08 PM, Jonathan Gray wrote:
> Make similiar changes to libglvnd to avoid a text relocation in
> x86 tsd stubs fixing the build with lld.
> 
> Signed-off-by: Jonathan Gray <jsg at jsg.id.au>
> Cc: mesa-stable at lists.freedesktop.org
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108541
> ---
>  src/mapi/entry_x86_tsd.h | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/src/mapi/entry_x86_tsd.h b/src/mapi/entry_x86_tsd.h
> index 0c28c8ff068..e08a02f3db2 100644
> --- a/src/mapi/entry_x86_tsd.h
> +++ b/src/mapi/entry_x86_tsd.h
> @@ -31,7 +31,7 @@
>  #define HIDDEN
>  #endif
>  
> -#define X86_ENTRY_SIZE 32
> +#define X86_ENTRY_SIZE 64
>  
>  __asm__(".text\n"
>          ".balign 32\n"
> @@ -44,12 +44,16 @@ __asm__(".text\n"
>     func ":"
>  
>  #define STUB_ASM_CODE(slot)         \
> -   "movl " ENTRY_CURRENT_TABLE ", %eax\n\t" \
> +   "call 1f\n\t"                    \
> +   "1:\n\t"                         \
> +   "popl %eax\n\t"                  \
> +   "addl $_GLOBAL_OFFSET_TABLE_+[.-1b], %eax\n\t" \
> +   "movl " ENTRY_CURRENT_TABLE "@GOT(%eax), %eax\n\t" \
> +   "mov (%eax), %eax\n\t"           \
>     "testl %eax, %eax\n\t"           \
> -   "je 1f\n\t"                      \
> -   "jmp *(4 * " slot ")(%eax)\n"    \
> +   "jne 1f\n\t"                     \
> +   "call " ENTRY_CURRENT_TABLE_GET "@PLT\n\t" \
>     "1:\n\t"                         \
> -   "call " ENTRY_CURRENT_TABLE_GET "\n\t" \
>     "jmp *(4 * " slot ")(%eax)"

After this change, the code is:

#define STUB_ASM_CODE(slot)         \
   "call 1f\n\t"                    \
   "1:\n\t"                         \
   "popl %eax\n\t"                  \
   "addl $_GLOBAL_OFFSET_TABLE_+[.-1b], %eax\n\t" \
   "movl " ENTRY_CURRENT_TABLE "@GOT(%eax), %eax\n\t" \
   "mov (%eax), %eax\n\t"           \
   "testl %eax, %eax\n\t"           \
   "jne 1f\n\t"                     \
   "call " ENTRY_CURRENT_TABLE_GET "@PLT\n\t" \
   "1:\n\t"                         \
   "jmp *(4 * " slot ")(%eax)"

So there's going to be two labels "1:".  Does that even assemble?