Patchwork Implement stap probe on ARM's unwinder

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Submitter Sergio Durigan Junior
Date Dec. 2, 2011, 6:35 p.m.
Message ID <m362hyizxy.fsf@redhat.com>
Download mbox | patch
Permalink /patch/128932/
State New
Headers show

Comments

Sergio Durigan Junior - Dec. 2, 2011, 6:35 p.m.
Ramana Radhakrishnan <ramana.radhakrishnan@linaro.org> writes:

> Sergio: Other than a few minor tweaks to the Changelog it largely
> looks obvious to me.

Hello Ramana,

Thanks for the review.  Here is the updated version of the patch.

I asked Tom Tromey to commit it for me, since I don't have write
permission on the repository.

Thank you again,

Sergio.

Patch

diff --git a/libgcc/ChangeLog b/libgcc/ChangeLog
index e7f18e2..0901cae 100644
--- a/libgcc/ChangeLog
+++ b/libgcc/ChangeLog
@@ -1,3 +1,14 @@ 
+2011-12-02  Sergio Durigan Junior  <sergiodj@redhat.com>
+
+	* unwind-arm-common.inc: Include `tconfig.h', `tsystem.h' and
+	`sys/sdt.h'.
+	(_Unwind_DebugHook): New function.
+	(uw_restore_core_regs): New define.
+	(unwind_phase2): Use uw_restore_core_regs instead of
+	restore_core_regs.
+	(unwind_phase2_forced): Likewise.
+	(__gnu_Unwind_Resume): Likewise.
+
 2011-11-30  John David Anglin  <dave.anglin@nrc-cnrc.gc.ca>
 
 	PR other/51272
diff --git a/libgcc/unwind-arm-common.inc b/libgcc/unwind-arm-common.inc
index 0713056..bf16902 100644
--- a/libgcc/unwind-arm-common.inc
+++ b/libgcc/unwind-arm-common.inc
@@ -21,8 +21,15 @@ 
    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
    <http://www.gnu.org/licenses/>.  */
 
+#include "tconfig.h"
+#include "tsystem.h"
 #include "unwind.h"
 
+/* Used for SystemTap unwinder probe.  */
+#ifdef HAVE_SYS_SDT_H
+#include <sys/sdt.h>
+#endif
+
 /* We add a prototype for abort here to avoid creating a dependency on
    target headers.  */
 extern void abort (void);
@@ -105,6 +112,44 @@  static inline _uw selfrel_offset31 (const _uw *p);
 
 static _uw __gnu_unwind_get_pr_addr (int idx);
 
+static void _Unwind_DebugHook (void *, void *)
+  __attribute__ ((__noinline__, __used__, __noclone__));
+
+/* This function is called during unwinding.  It is intended as a hook
+   for a debugger to intercept exceptions.  CFA is the CFA of the
+   target frame.  HANDLER is the PC to which control will be
+   transferred.  */
+
+static void
+_Unwind_DebugHook (void *cfa __attribute__ ((__unused__)),
+		   void *handler __attribute__ ((__unused__)))
+{
+  /* We only want to use stap probes starting with v3.  Earlier
+     versions added too much startup cost.  */
+#if defined (HAVE_SYS_SDT_H) && defined (STAP_PROBE2) && _SDT_NOTE_TYPE >= 3
+  STAP_PROBE2 (libgcc, unwind, cfa, handler);
+#else
+  asm ("");
+#endif
+}
+
+/* This is a wrapper to be called when we need to restore core registers.
+   It will call `_Unwind_DebugHook' before restoring the registers, thus
+   making it possible to intercept and debug exceptions.
+
+   When calling `_Unwind_DebugHook', the first argument (the CFA) is zero
+   because we are not interested in it.  However, it must be there (even
+   being zero) because GDB expects to find it when using the probe.  */
+
+#define uw_restore_core_regs(TARGET, CORE)				      \
+  do									      \
+    {									      \
+      void *handler = __builtin_frob_return_addr ((void *) VRS_PC (TARGET));  \
+      _Unwind_DebugHook (0, handler);					      \
+      restore_core_regs (CORE);						      \
+    }									      \
+  while (0)
+
 /* Perform a binary search for RETURN_ADDRESS in TABLE.  The table contains
    NREC entries.  */
 
@@ -253,8 +298,8 @@  unwind_phase2 (_Unwind_Control_Block * ucbp, phase2_vrs * vrs)
   
   if (pr_result != _URC_INSTALL_CONTEXT)
     abort();
-  
-  restore_core_regs (&vrs->core);
+
+  uw_restore_core_regs (vrs, &vrs->core);
 }
 
 /* Perform phase2 forced unwinding.  */
@@ -339,7 +384,7 @@  unwind_phase2_forced (_Unwind_Control_Block *ucbp, phase2_vrs *entry_vrs,
       return _URC_FAILURE;
     }
 
-  restore_core_regs (&saved_vrs.core);
+  uw_restore_core_regs (&saved_vrs, &saved_vrs.core);
 }
 
 /* This is a very limited implementation of _Unwind_GetCFA.  It returns
@@ -450,7 +495,7 @@  __gnu_Unwind_Resume (_Unwind_Control_Block * ucbp, phase2_vrs * entry_vrs)
     {
     case _URC_INSTALL_CONTEXT:
       /* Upload the registers to enter the landing pad.  */
-      restore_core_regs (&entry_vrs->core);
+      uw_restore_core_regs (entry_vrs, &entry_vrs->core);
 
     case _URC_CONTINUE_UNWIND:
       /* Continue unwinding the next frame.  */