i386 TLS_INIT_TP might produce bogus asm changing stack pointer.

  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.

https://bugzilla.redhat.com/show_bug.cgi?id=1133134

	* sysdeps/i386/nptl/tls.h (TLS_INIT_TP): Use INTERNAL_SYSCALL
	to call set_thread_area instead of hand written asm.
---
 ChangeLog               | 5 +++++
 sysdeps/i386/nptl/tls.h | 8 ++------
 2 files changed, 7 insertions(+), 6 deletions(-)
  

On 08/26/2014 10:27 AM, Mark Wielaard wrote:
> 	* sysdeps/i386/nptl/tls.h (TLS_INIT_TP): Use INTERNAL_SYSCALL
> 	to call set_thread_area instead of hand written asm.

Patch looks good, but you can remove these #defines now:

# 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

(INTERNAL_SYSCALL is not affected by this issue because it uses explicit 
register constraints, and not the general "r" constraint.)