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authorChris Metcalf <cmetcalf@ezchip.com>2015-07-21 12:04:52 -0400
committerChris Metcalf <cmetcalf@ezchip.com>2015-07-21 12:11:55 -0400
commit0ac4f1dab3e5778c79994a89111b4eb1d247ab12 (patch)
treebcc24bc8dd8a2c2b879e38a1c97234d9fcf420ba
parentf30d94a74a30b832354d4b87c23a4909ed24b929 (diff)
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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.
-rw-r--r--ChangeLog7
-rw-r--r--sysdeps/unix/sysv/linux/tile/makecontext.c8
-rw-r--r--sysdeps/unix/sysv/linux/tile/setcontext.S2
3 files changed, 13 insertions, 4 deletions
diff --git a/ChangeLog b/ChangeLog
index 490c0acf96..d855f769e1 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 b14b8d5cc9..c77d005672 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 ee9edbefe1..02d6a1578c 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