Re: [PATCH] libebl: Add ebl_unwind_ret_mask.

[Mark Wielaard <mjw at redhat dot com>]

On Sun, 2014-06-15 at 21:59 +0200, Kurt Roeckx wrote:
> On Sun, Jun 15, 2014 at 09:27:32PM +0200, Kurt Roeckx wrote:
> > 
> > I'm not sure what that code is doing there.  But it seems to be
> > looking at a 64 bit core file (x86_64, arm64, s390x) and then
> > create a 64 bit pointer is trying to dereference that.
> 
> That would be a pointer to a 64 bit object of course.  Sparc
> probably has stricter alignment requirements than the other
> arches.  I just wonder why it worked before.

Indeed. You seem to be right that we are trying to read possibly
unaligned data which would cause a bus error on sparc. There was even a
helpful FIXME in the code about it. Why we didn't see that before is a
mystery. But the attached patch should solve it. Could you test it?

Thanks,

Mark

>From 7a6d8a0e3694af48a38e0461e15fcde0a06bad58 Mon Sep 17 00:00:00 2001
From: Mark Wielaard <mjw@redhat.com>
Date: Sun, 15 Jun 2014 22:14:04 +0200
Subject: [PATCH] libdwfl: linux-core-attach.c handle possible unaligned data access.

Use libdw/memory-access.h macros read_4ubyte_unaligned_noncvt and
read_8ubyte_unaligned_noncvt to access possibly unaligned data in
core files.

Signed-off-by: Mark Wielaard <mjw@redhat.com>
---
 libdwfl/ChangeLog           |    9 +++++++++
 libdwfl/linux-core-attach.c |   22 +++++++++++-----------
 2 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index ac92a21..f1bc1a7 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,3 +1,12 @@
+2014-06-15  Mark Wielaard  <mjw@redhat.com>
+
+	* linux-core-attach.c (core_memory_read): Use libdw/memory-access.h
+	macros read_4ubyte_unaligned_noncvt and read_8ubyte_unaligned_noncvt
+	to read possibly unaligned data.
+	(core_next_thread): Likewise.
+	(core_set_initial_registers): Likewise.
+	(dwfl_core_file_attach): Likewise.
+
 2014-06-11  Mark Wielaard  <mjw@redhat.com>
 
 	* dwfl_frame.c (__libdwfl_process_free): Reset dwfl->attacherr.
diff --git a/libdwfl/linux-core-attach.c b/libdwfl/linux-core-attach.c
index 7ef3f25..5a7b3b3 100644
--- a/libdwfl/linux-core-attach.c
+++ b/libdwfl/linux-core-attach.c
@@ -30,6 +30,8 @@
 #include <fcntl.h>
 #include "system.h"
 
+#include "../libdw/memory-access.h"
+
 #ifndef MIN
 # define MIN(a, b) ((a) < (b) ? (a) : (b))
 #endif
@@ -83,12 +85,10 @@ core_memory_read (Dwfl *dwfl, Dwarf_Addr addr, Dwarf_Word *result,
 	  return false;
 	}
       assert (data->d_size == bytes);
-      /* FIXME: Currently any arch supported for unwinding supports
-	 unaligned access.  */
       if (bytes == 8)
-	*result = *(const uint64_t *) data->d_buf;
+	*result = read_8ubyte_unaligned_noncvt (data->d_buf);
       else
-	*result = *(const uint32_t *) data->d_buf;
+	*result = read_4ubyte_unaligned_noncvt (data->d_buf);
       return true;
     }
   __libdwfl_seterrno (DWFL_E_ADDR_OUTOFRANGE);
@@ -150,7 +150,7 @@ core_next_thread (Dwfl *dwfl __attribute__ ((unused)), void *dwfl_arg,
 	  break;
       if (item == items + nitems)
 	continue;
-      uint32_t val32 = *(const uint32_t *) (desc + item->offset);
+      uint32_t val32 = read_4ubyte_unaligned_noncvt (desc + item->offset);
       val32 = (elf_getident (core, NULL)[EI_DATA] == ELFDATA2MSB
 		? be32toh (val32) : le32toh (val32));
       pid_t tid = (int32_t) val32;
@@ -201,7 +201,7 @@ core_set_initial_registers (Dwfl_Thread *thread, void *thread_arg_voidp)
   assert (item < items + nitems);
   pid_t tid;
   {
-    uint32_t val32 = *(const uint32_t *) (desc + item->offset);
+    uint32_t val32 = read_4ubyte_unaligned_noncvt (desc + item->offset);
     val32 = (elf_getident (core, NULL)[EI_DATA] == ELFDATA2MSB
 	     ? be32toh (val32) : le32toh (val32));
     tid = (int32_t) val32;
@@ -218,14 +218,14 @@ core_set_initial_registers (Dwfl_Thread *thread, void *thread_arg_voidp)
       switch (gelf_getclass (core) == ELFCLASS32 ? 32 : 64)
       {
 	case 32:;
-	  uint32_t val32 = *(const uint32_t *) (desc + item->offset);
+	  uint32_t val32 = read_4ubyte_unaligned_noncvt (desc + item->offset);
 	  val32 = (elf_getident (core, NULL)[EI_DATA] == ELFDATA2MSB
 		   ? be32toh (val32) : le32toh (val32));
 	  /* Do a host width conversion.  */
 	  pc = val32;
 	  break;
 	case 64:;
-	  uint64_t val64 = *(const uint64_t *) (desc + item->offset);
+	  uint64_t val64 = read_8ubyte_unaligned_noncvt (desc + item->offset);
 	  val64 = (elf_getident (core, NULL)[EI_DATA] == ELFDATA2MSB
 		   ? be64toh (val64) : le64toh (val64));
 	  pc = val64;
@@ -259,7 +259,7 @@ core_set_initial_registers (Dwfl_Thread *thread, void *thread_arg_voidp)
 	  switch (regloc->bits)
 	  {
 	    case 32:;
-	      uint32_t val32 = *(const uint32_t *) reg_desc;
+	      uint32_t val32 = read_4ubyte_unaligned_noncvt (reg_desc);
 	      reg_desc += sizeof val32;
 	      val32 = (elf_getident (core, NULL)[EI_DATA] == ELFDATA2MSB
 		       ? be32toh (val32) : le32toh (val32));
@@ -267,7 +267,7 @@ core_set_initial_registers (Dwfl_Thread *thread, void *thread_arg_voidp)
 	      val = val32;
 	      break;
 	    case 64:;
-	      uint64_t val64 = *(const uint64_t *) reg_desc;
+	      uint64_t val64 = read_8ubyte_unaligned_noncvt (reg_desc);
 	      reg_desc += sizeof val64;
 	      val64 = (elf_getident (core, NULL)[EI_DATA] == ELFDATA2MSB
 		       ? be64toh (val64) : le64toh (val64));
@@ -392,7 +392,7 @@ dwfl_core_file_attach (Dwfl *dwfl, Elf *core)
 	  break;
       if (item == items + nitems)
 	continue;
-      uint32_t val32 = *(const uint32_t *) (desc + item->offset);
+      uint32_t val32 = read_4ubyte_unaligned_noncvt (desc + item->offset);
       val32 = (elf_getident (core, NULL)[EI_DATA] == ELFDATA2MSB
 		? be32toh (val32) : le32toh (val32));
       pid = (int32_t) val32;
-- 
1.7.1