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 490c0acf962f73d000931ccd9cb64ec353b429e0..d855f769e19ebeb26fe9388ed789c25bb49ef5d2 100644 (file)
--- 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 b14b8d5cc91fc2f5c4291d870de50a6e5200b327..c77d00567296a358c8b8e97d581c9e84822ae826 100644 (file)
--- 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 ee9edbefe1bb5525690f537b8c535dd1274f9c2c..02d6a1578c7557a961616e893f2255b22a541ac5 100644 (file)
--- 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