mips: terminate the FDE before the return trampoline in makecontext

In makecontext the FDE needs to be terminated before the return
trampoline otherwise backtrace called within a context created by
makecontext yields infinite backtrace.

This bug has been present for a long time, stdlib/tst-makecontext did
not fail until recent commit e535ce2. Tested on mips-linux-gnu and
mips64el-linux-gnuabi64 and mips-linux-gnu, no regression.

This fixes stdlib/tst-makecontext on MIPS.

Changelog:
	[BZ #19792]
	* sysdeps/unix/sysv/linux/mips/makecontext.S (__makecontext):
	Terminate FDE before return label.

ChangeLog

@@ -1,3 +1,9 @@
+2016-03-09  Aurelien Jarno  <aurelien@aurel32.net>
+
+	[BZ #19792]
+	* sysdeps/unix/sysv/linux/mips/makecontext.S (__makecontext):
+	Terminate FDE before return label.
+
 2016-03-09  Joseph Myers  <joseph@codesourcery.com>
 
 	[BZ #19790]

sysdeps/unix/sysv/linux/mips/makecontext.S

@@ -153,6 +153,11 @@ NESTED (__makecontext, FRAMESZ, ra)
 #endif
 	jr	ra
 
+	/* We need to terminate the FDE to stop unwinding if backtrace was
+	   called within a context created by makecontext.  */
+	cfi_endproc
+	nop
+
 99:
 #ifdef __PIC__
 	move	gp, s1
@@ -186,6 +191,8 @@ NESTED (__makecontext, FRAMESZ, ra)
 1:
 	lb	zero, (zero)
 	b	1b
+
+	cfi_startproc
 PSEUDO_END (__makecontext)
 
 weak_alias (__makecontext, makecontext)