svn commit: r268310 - head/libexec/rtld-elf/arm

[Andrew Turner]

Author: andrew
Date: Sun Jul  6 10:24:06 2014
New Revision: 268310
URL: http://svnweb.freebsd.org/changeset/base/268310

Log:
  Align the stack in _rtld_bind_start. Normally this is called with the
  correct stack alignment, however when we have a leaf function that uses
  thread local storage it calls __aeabi_read_tp to get the thread pointer.
  Neither GCC or clang see this as a function call so will align the stack
  to a 4-byte boundary. This may be a problem as _rtld_bind expects to be
  on an 8-byte boundary.
  
  The solution is to store a copy of the stack pointer and force the
  alignment before calling _rtld_bind.
  
  This fixes a problem with armeb where applications would crash in odd ways.
  It should also remove the need for a local patch to clang to force the
  stack alignment to an 8-byte boundary, even for leaf functions. Further
  testing will be needed before reverting this local change to clang as we
  may rely on it in other places.
  
  Reviewed by:	jmg@

Modified:
  head/libexec/rtld-elf/arm/rtld_start.S

Modified: head/libexec/rtld-elf/arm/rtld_start.S
==============================================================================
--- head/libexec/rtld-elf/arm/rtld_start.S	Sun Jul  6 07:34:18 2014	(r268309)
+++ head/libexec/rtld-elf/arm/rtld_start.S	Sun Jul  6 10:24:06 2014	(r268310)
@@ -77,7 +77,7 @@ __FBSDID("$FreeBSD$");
  *	lr = &GOT[2]
  */
 _rtld_bind_start:
-	stmdb	sp!,{r0-r4,sl,fp}
+	stmdb	sp!,{r0-r5,sl,fp}
 
 	sub	r1, ip, lr		/* r1 = 4 * (n + 1) */
 	sub	r1, r1, #4		/* r1 = 4 * n */
@@ -86,11 +86,14 @@ _rtld_bind_start:
 	ldr	r0, [lr, #-4]		/* get obj ptr from GOT[1] */
 	mov	r4, ip			/* save GOT location */
 
+	mov	r5, sp			/* Save the stack pointer */
+	bic	sp, sp, #7		/* Align the stack pointer */
 	bl	_rtld_bind		/* Call the binder */
+	mov	sp, r5			/* Restore the old stack pointer */
 
 	str	r0, [r4]		/* save address in GOT */
 	mov	ip, r0			/* save new address */
 
-	ldmia	sp!,{r0-r4,sl,fp,lr}	/* restore the stack */
+	ldmia	sp!,{r0-r5,sl,fp,lr}	/* restore the stack */
 	mov	pc, ip			/* jump to the new address */