commit a85abfa92220239cad0a8a6b0f2a223f5e6472a9

Author: Andreas Schwab <schwab@suse.de>

Date:   Thu Aug 18 11:38:28 2016 +0200

    arm: mark __startcontext as .cantunwind (bug 20435)

    __startcontext marks the bottom of the call stack of the contexts created

    by makecontext.

    (cherry picked from commit 9e2ff6c9cc54c0b4402b8d49e4abe7000fde7617)

    Also includes the NEWS update, cherry-picked from commits

    056dd72af83f5459ce6d545a49dea6dba7d635dc and

    4d047efdbc55b0d68947cde682e5363d16a66294.

diff --git a/sysdeps/unix/sysv/linux/arm/setcontext.S b/sysdeps/unix/sysv/linux/arm/setcontext.S

index 24c7294..926b65a 100644

--- 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