i386 TLS_INIT_TP might produce bogus asm changing stack pointer [BZ #17319]

TLS_INIT_TP in sysdeps/i386/nptl/tls.h uses some hand written asm to
generate a set_thread_area that might result in exchanging ebx and esp
around the syscall causing introspection tools like valgrind to loose
track of the user stack. Just use INTERNAL_SYSCALL which makes sure
esp isn't changed arbitrarily.

Before the patch the code would generate:

mov    $0xf3,%eax
movl   $0xfffff,0x8(%esp)
movl   $0x51,0xc(%esp)
xchg   %esp,%ebx
int    $0x80
xchg   %esp,%ebx

Using INTERNAL_SYSCALL instead will generate:

movl   $0xfffff,0x8(%esp)
movl   $0x51,0xc(%esp)
xchg   %ecx,%ebx
mov    $0xf3,%eax
int    $0x80
xchg   %ecx,%ebx

Thanks to Florian Weimer for analysing why the original code generated
the bogus esp usage:

  _segdescr.desc happens to be at the top of the stack, so its address
  is in %esp.  The asm statement says that %3 is an input, so its value
  will not change, and GCC can use %esp as the input register for the
  expression &_segdescr.desc.  But the constraints do not fully describe
  the asm statement because the %3 register is actually modified, albeit
  only temporarily.

	[BZ #17319]
	* sysdeps/i386/nptl/tls.h (TLS_INIT_TP): Use INTERNAL_SYSCALL
	to call set_thread_area instead of hand written asm.
	(__NR_set_thread_area): Removed define.
	(TLS_FLAG_WRITABLE): Likewise.
	(__ASSUME_SET_THREAD_AREA): Remove check.
	(TLS_EBX_ARG): Remove define.
	(TLS_LOAD_EBX): Likewise.

1 files changed, 2 insertions, 29 deletions

diff --git a/sysdeps/i386/nptl/tls.h b/sysdeps/i386/nptl/tls.h
index ac9c9a22f9..d7302ba8aa 100644
--- a/sysdeps/i386/nptl/tls.h
+++ b/sysdeps/i386/nptl/tls.h
@@ -154,29 +154,6 @@ union user_desc_init
   __asm ("movw %w0, %%gs" :: "q" (val))
 # endif
 
-
-# ifndef __NR_set_thread_area
-#  define __NR_set_thread_area 243
-# endif
-# ifndef TLS_FLAG_WRITABLE
-#  define TLS_FLAG_WRITABLE		0x00000001
-# endif
-
-// XXX Enable for the real world.
-#if 0
-# ifndef __ASSUME_SET_THREAD_AREA
-#  error "we need set_thread_area"
-# endif
-#endif
-
-# ifdef __PIC__
-#  define TLS_EBX_ARG "r"
-#  define TLS_LOAD_EBX "xchgl %3, %%ebx\n\t"
-# else
-#  define TLS_EBX_ARG "b"
-#  define TLS_LOAD_EBX
-# endif
-
 #if defined NEED_DL_SYSINFO
 # define INIT_SYSINFO \
   _head->sysinfo = GLRO(dl_sysinfo)
@@ -231,12 +208,8 @@ tls_fill_user_desc (union user_desc_init *desc,
      tls_fill_user_desc (&_segdescr, -1, _thrdescr);			      \
 									      \
      /* Install the TLS.  */						      \
-     asm volatile (TLS_LOAD_EBX						      \
-		   "int $0x80\n\t"					      \
-		   TLS_LOAD_EBX						      \
-		   : "=a" (_result), "=m" (_segdescr.desc.entry_number)	      \
-		   : "0" (__NR_set_thread_area),			      \
-		     TLS_EBX_ARG (&_segdescr.desc), "m" (_segdescr.desc));    \
+     INTERNAL_SYSCALL_DECL (err);					      \
+     _result = INTERNAL_SYSCALL (set_thread_area, err, 1, &_segdescr.desc);   \
 									      \
      if (_result == 0)							      \
        /* We know the index in the GDT, now load the segment register.	      \