GNU C Library master sources branch master updated. glibc-2.21-626-g0ac4f1d

[cmetcalf at sourceware dot org]

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http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=0ac4f1dab3e5778c79994a89111b4eb1d247ab12

commit 0ac4f1dab3e5778c79994a89111b4eb1d247ab12
Author: Chris Metcalf <cmetcalf@ezchip.com>
Date:   Tue Jul 21 12:04:52 2015 -0400

    tile: Fix BZ #18508 (makecontext yield infinite backtrace)
    
    It turns out tile suffered from the same problem as S390.  However,
    disabling CFI information for the __startcontext on tile was not
    sufficient to fix the problem; I think the backtracer will just
    blindly try to follow the link register (lr) in that case.
    
    Instead, the change adds a cfi_undefined directive for "lr"
    and then arranges to call __startcontext directly when the new
    context starts, rather than just synthesizing a return to it.
    In addition to being a bit easier now to understand the control
    flow, this also allows the cfi_undefined directive to be placed in
    a way that causes it to be in force at the address that the "lr"
    from the called function points to.

diff --git a/ChangeLog b/ChangeLog
index 490c0ac..d855f76 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2015-07-21  Chris Metcalf  <cmetcalf@ezchip.com>
+
+	* sysdeps/unix/sysv/linux/tile/makecontext.c (__makecontext): Call
+	__startcontext to initialize the new context.
+	* sysdeps/unix/sysv/linux/tile/setcontext.S (__startcontext): Set
+	up CFI directive to forbid further backtracing.
+
 2015-07-21  Marko Myllynen  <myllynen@redhat.com>
 
 	* charmaps/ANSI_X3.110-1983: Remove obsolete repertoire map
diff --git a/sysdeps/unix/sysv/linux/tile/makecontext.c b/sysdeps/unix/sysv/linux/tile/makecontext.c
index b14b8d5..c77d005 100644
--- a/sysdeps/unix/sysv/linux/tile/makecontext.c
+++ b/sysdeps/unix/sysv/linux/tile/makecontext.c
@@ -52,14 +52,14 @@ __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
     }
   va_end (ap);
 
-  /* Pass (*func) to __startcontext in pc.  */
-  ucp->uc_mcontext.pc = (long) func;
+  /* Start in the trampoline.  */
+  ucp->uc_mcontext.pc = (long) __startcontext;
 
   /* Set stack pointer.  */
   ucp->uc_mcontext.sp = (long) sp;
 
-  /* Set the return address to trampoline.  */
-  ucp->uc_mcontext.lr = (long) __startcontext;
+  /* Pass FUNC to __startcontext in r31.  */
+  ucp->uc_mcontext.gregs[31] = (long) func;
 
   /* Pass ucp->uc_link to __startcontext in r30.  */
   ucp->uc_mcontext.gregs[30] = (long) ucp->uc_link;
diff --git a/sysdeps/unix/sysv/linux/tile/setcontext.S b/sysdeps/unix/sysv/linux/tile/setcontext.S
index ee9edbe..02d6a15 100644
--- a/sysdeps/unix/sysv/linux/tile/setcontext.S
+++ b/sysdeps/unix/sysv/linux/tile/setcontext.S
@@ -190,7 +190,9 @@ END (__setcontext)
 weak_alias (__setcontext, setcontext)
 
 ENTRY (__startcontext)
+	cfi_undefined (lr)
 	FEEDBACK_ENTER(__startcontext)
+	jalr r31
 	BEQZ r30, 1f
 	{
 	 move r0, r30

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                                  |    7 +++++++
 sysdeps/unix/sysv/linux/tile/makecontext.c |    8 ++++----
 sysdeps/unix/sysv/linux/tile/setcontext.S  |    2 ++
 3 files changed, 13 insertions(+), 4 deletions(-)


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