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

[Emil Velikov]

On Fri, 2 Nov 2018 at 00:02, Jonathan Gray <jsg at jsg.id.au> wrote:
>
> On Thu, Nov 01, 2018 at 12:26:34PM -0700, Ian Romanick wrote:
> > 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?
>
> Yes, the call/jmp is always forward as it is '1f'.
> This also runs glxinfo, glxgears etc on a pentium m running OpenBSD/i386.
>
> https://github.com/NVIDIA/libglvnd/blob/master/src/GLdispatch/vnd-glapi/entry_x86_tsd.c#L58
>
> libglvnd has two labels like this as well, the ebx use there isn't needed.

Hi all, did this get stuck or it's superseded/obsolete?

-Emil