arm: mark __startcontext as .cantunwind (bug 20435)

__startcontext marks the bottom of the call stack of the contexts created
by makecontext.

diff --git a/ChangeLog b/ChangeLog
index 1e35b52ea2da21cc74a1f58616e1c39b610ed055..62f60dceeab2cc7234cd2be0920a1e172df391a6 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2016-08-15  Andreas Schwab  <schwab@suse.de>
+
+       [BZ #20435]
+       * sysdeps/unix/sysv/linux/arm/setcontext.S (__startcontext): Mark
+       as .cantunwind.
+
 2016-08-12  Joseph Myers  <joseph@codesourcery.com>
 
        * sysdeps/powerpc/fpu/fsetexcptflg.c (__fesetexceptflag): Add

diff --git a/sysdeps/unix/sysv/linux/arm/setcontext.S b/sysdeps/unix/sysv/linux/arm/setcontext.S
index 603e508858b491c6973552bd680bf3fc927f4714..d1f168fece80fd55bc79946f849c6fab4ff43e1b 100644 (file)
--- a/sysdeps/unix/sysv/linux/arm/setcontext.S
+++ b/sysdeps/unix/sysv/linux/arm/setcontext.S
@@ -86,12 +86,19 @@ weak_alias(__setcontext, setcontext)
 
        /* Called when a makecontext() context returns.  Start the
           context in R4 or fall through to exit().  */
+       /* Unwind descriptors are looked up based on PC - 2, so we have to
+          make sure to mark the instruction preceding the __startcontext
+          label as .cantunwind.  */
+       .fnstart
+       .cantunwind
+       nop
 ENTRY(__startcontext)
        movs    r0, r4
        bne     PLTJMP(__setcontext)
 
        @ New context was 0 - exit
        b       PLTJMP(HIDDEN_JUMPTARGET(exit))
+       .fnend
 END(__startcontext)
 
 #ifdef PIC