[Mesa-dev] [PATCH v2] mapi: avoid text relocation in x86 tsd stubs

[Jonathan Gray]

On Sun, Nov 11, 2018 at 03:47:35PM +1100, Jonathan Gray wrote:
> Make similiar changes to libglvnd to avoid a text relocation in
> x86 tsd stubs fixing the build with lld.
> 
> v2:
>   - store the address of the GOT in ebx required before calling PLT stub
>   - change .balign values to match X86_ENTRY_SIZE

When a different version of this patch was committed/pushed in
45206d7673adb1484cbdb3eadaf82e0849c9cdcf
(with author rewritten to imply I wrote the commit message)
it did not include the .balign changes to match the entry size change.

Was this purposefully skipped or overlooked as the bugzilla patch was
used?

The diff to what was committed and this patch is

diff --git a/src/mapi/entry_x86_tsd.h b/src/mapi/entry_x86_tsd.h
index bd8db7b19f9..1dec3ed86c4 100644
--- a/src/mapi/entry_x86_tsd.h
+++ b/src/mapi/entry_x86_tsd.h
@@ -34,18 +34,18 @@
 #define X86_ENTRY_SIZE 64
 
 __asm__(".text\n"
-        ".balign 32\n"
+        ".balign " U_STRINGIFY(X86_ENTRY_SIZE) "\n"
         "x86_entry_start:");
 
 #define STUB_ASM_ENTRY(func)        \
    ".globl " func "\n"              \
    ".type " func ", @function\n"    \
-   ".balign 32\n"                   \
+   ".balign " U_STRINGIFY(X86_ENTRY_SIZE) "\n" \
    func ":"
 
 #define STUB_ASM_CODE(slot)         \
    "push %ebx\n\t"                  \
-   "call 1f\n\t"                    \
+   "call 1f\n"                      \
    "1:\n\t"                         \
    "popl %ebx\n\t"                  \
    "addl $_GLOBAL_OFFSET_TABLE_+[.-1b], %ebx\n\t" \
@@ -53,7 +53,7 @@ __asm__(".text\n"
    "mov (%eax), %eax\n\t"           \
    "testl %eax, %eax\n\t"           \
    "jne 1f\n\t"                     \
-   "call " ENTRY_CURRENT_TABLE_GET "@PLT\n\t" \
+   "call " ENTRY_CURRENT_TABLE_GET "@PLT\n" \
    "1:\n\t"                         \
    "pop %ebx\n\t"                   \
    "jmp *(4 * " slot ")(%eax)"
@@ -63,7 +63,7 @@ __asm__(".text\n"
 
 #ifndef MAPI_MODE_BRIDGE
 
-__asm__(".balign 32\n"
+__asm__(".balign " U_STRINGIFY(X86_ENTRY_SIZE) "\n"
         "x86_entry_end:");
 
 #include <string.h>

> 
> 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 | 22 ++++++++++++++--------
>  1 file changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/src/mapi/entry_x86_tsd.h b/src/mapi/entry_x86_tsd.h
> index 0c28c8ff068..1dec3ed86c4 100644
> --- a/src/mapi/entry_x86_tsd.h
> +++ b/src/mapi/entry_x86_tsd.h
> @@ -31,25 +31,31 @@
>  #define HIDDEN
>  #endif
>  
> -#define X86_ENTRY_SIZE 32
> +#define X86_ENTRY_SIZE 64
>  
>  __asm__(".text\n"
> -        ".balign 32\n"
> +        ".balign " U_STRINGIFY(X86_ENTRY_SIZE) "\n"
>          "x86_entry_start:");
>  
>  #define STUB_ASM_ENTRY(func)        \
>     ".globl " func "\n"              \
>     ".type " func ", @function\n"    \
> -   ".balign 32\n"                   \
> +   ".balign " U_STRINGIFY(X86_ENTRY_SIZE) "\n" \
>     func ":"
>  
>  #define STUB_ASM_CODE(slot)         \
> -   "movl " ENTRY_CURRENT_TABLE ", %eax\n\t" \
> +   "push %ebx\n\t"                  \
> +   "call 1f\n"                      \
> +   "1:\n\t"                         \
> +   "popl %ebx\n\t"                  \
> +   "addl $_GLOBAL_OFFSET_TABLE_+[.-1b], %ebx\n\t" \
> +   "movl " ENTRY_CURRENT_TABLE "@GOT(%ebx), %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" \
>     "1:\n\t"                         \
> -   "call " ENTRY_CURRENT_TABLE_GET "\n\t" \
> +   "pop %ebx\n\t"                   \
>     "jmp *(4 * " slot ")(%eax)"
>  
>  #define MAPI_TMP_STUB_ASM_GCC
> @@ -57,7 +63,7 @@ __asm__(".text\n"
>  
>  #ifndef MAPI_MODE_BRIDGE
>  
> -__asm__(".balign 32\n"
> +__asm__(".balign " U_STRINGIFY(X86_ENTRY_SIZE) "\n"
>          "x86_entry_end:");
>  
>  #include <string.h>
> -- 
> 2.19.1
> 
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