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[PATCH 1/9] [libbacktrace] Read .gnu_debugaltlink


Read the elf file pointed at by the .gnu_debugaltlink section, and verify that
the build id matches.

2018-11-11  Tom de Vries  <tdevries@suse.de>

	* elf.c (elf_add): Add and handle with_buildid_data and
	with_buildid_size parameters.  Handle .gnu_debugaltlink section.
	(phdr_callback, backtrace_initialize): Add arguments to elf_add calls.
---
 libbacktrace/elf.c | 95 +++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 90 insertions(+), 5 deletions(-)

diff --git a/libbacktrace/elf.c b/libbacktrace/elf.c
index f4863f0bea5..f3bc2119c07 100644
--- a/libbacktrace/elf.c
+++ b/libbacktrace/elf.c
@@ -2638,7 +2638,8 @@ static int
 elf_add (struct backtrace_state *state, const char *filename, int descriptor,
 	 uintptr_t base_address, backtrace_error_callback error_callback,
 	 void *data, fileline *fileline_fn, int *found_sym, int *found_dwarf,
-	 int exe, int debuginfo)
+	 int exe, int debuginfo, const char *with_buildid_data,
+	 uint32_t with_buildid_size)
 {
   struct backtrace_view ehdr_view;
   b_elf_ehdr ehdr;
@@ -2670,6 +2671,11 @@ elf_add (struct backtrace_state *state, const char *filename, int descriptor,
   int debuglink_view_valid;
   const char *debuglink_name;
   uint32_t debuglink_crc;
+  struct backtrace_view debugaltlink_view;
+  int debugaltlink_view_valid;
+  const char *debugaltlink_name;
+  const char *debugaltlink_buildid_data;
+  uint32_t debugaltlink_buildid_size;
   off_t min_offset;
   off_t max_offset;
   struct backtrace_view debug_view;
@@ -2694,6 +2700,10 @@ elf_add (struct backtrace_state *state, const char *filename, int descriptor,
   debuglink_view_valid = 0;
   debuglink_name = NULL;
   debuglink_crc = 0;
+  debugaltlink_view_valid = 0;
+  debugaltlink_name = NULL;
+  debugaltlink_buildid_data = NULL;
+  debugaltlink_buildid_size = 0;
   debug_view_valid = 0;
   opd = NULL;
 
@@ -2873,6 +2883,15 @@ elf_add (struct backtrace_state *state, const char *filename, int descriptor,
 	      buildid_data = &note->name[0] + ((note->namesz + 3) & ~ 3);
 	      buildid_size = note->descsz;
 	    }
+
+	  if (with_buildid_size != 0)
+	    {
+	      if (buildid_size != with_buildid_size)
+		goto fail;
+
+	      if (memcmp (buildid_data, with_buildid_data, buildid_size) != 0)
+		goto fail;
+	    }
 	}
 
       /* Read the debuglink file if present.  */
@@ -2899,6 +2918,27 @@ elf_add (struct backtrace_state *state, const char *filename, int descriptor,
 	    }
 	}
 
+      if (!debugaltlink_view_valid
+	  && strcmp (name, ".gnu_debugaltlink") == 0)
+	{
+	  const char *debugaltlink_data;
+	  size_t debugaltlink_name_len;
+
+	  if (!backtrace_get_view (state, descriptor, shdr->sh_offset,
+				   shdr->sh_size, error_callback, data,
+				   &debugaltlink_view))
+	    goto fail;
+
+	  debugaltlink_view_valid = 1;
+	  debugaltlink_data = (const char *) debugaltlink_view.data;
+	  debugaltlink_name = debugaltlink_data;
+	  debugaltlink_name_len = strnlen (debugaltlink_data, shdr->sh_size);
+	  debugaltlink_buildid_data = (debugaltlink_data
+				       + debugaltlink_name_len
+				       + 1);
+	  debugaltlink_buildid_size = shdr->sh_size - debugaltlink_name_len - 1;
+	}
+
       /* Read the .opd section on PowerPC64 ELFv1.  */
       if (ehdr.e_machine == EM_PPC64
 	  && (ehdr.e_flags & EF_PPC64_ABI) < 2
@@ -2993,8 +3033,11 @@ elf_add (struct backtrace_state *state, const char *filename, int descriptor,
 	  if (debuglink_view_valid)
 	    backtrace_release_view (state, &debuglink_view, error_callback,
 				    data);
+	  if (debugaltlink_view_valid)
+	    backtrace_release_view (state, &debugaltlink_view, error_callback,
+				    data);
 	  ret = elf_add (state, NULL, d, base_address, error_callback, data,
-			 fileline_fn, found_sym, found_dwarf, 0, 1);
+			 fileline_fn, found_sym, found_dwarf, 0, 1, NULL, 0);
 	  if (ret < 0)
 	    backtrace_close (d, error_callback, data);
 	  else
@@ -3028,8 +3071,11 @@ elf_add (struct backtrace_state *state, const char *filename, int descriptor,
 
 	  backtrace_release_view (state, &debuglink_view, error_callback,
 				  data);
+	  if (debugaltlink_view_valid)
+	    backtrace_release_view (state, &debugaltlink_view, error_callback,
+				    data);
 	  ret = elf_add (state, NULL, d, base_address, error_callback, data,
-			 fileline_fn, found_sym, found_dwarf, 0, 1);
+			 fileline_fn, found_sym, found_dwarf, 0, 1, NULL, 0);
 	  if (ret < 0)
 	    backtrace_close (d, error_callback, data);
 	  else
@@ -3044,6 +3090,43 @@ elf_add (struct backtrace_state *state, const char *filename, int descriptor,
       debuglink_view_valid = 0;
     }
 
+  if (debugaltlink_name != NULL)
+    {
+      int d;
+
+      d = elf_open_debugfile_by_debuglink (state, filename, debugaltlink_name,
+					   0, error_callback, data);
+      if (d >= 0)
+	{
+	  int ret;
+
+	  ret = elf_add (state, filename, d, base_address, error_callback, data,
+			 fileline_fn, found_sym, found_dwarf, 0, 1,
+			 debugaltlink_buildid_data, debugaltlink_buildid_size);
+	  backtrace_release_view (state, &debugaltlink_view, error_callback,
+				  data);
+	  debugaltlink_view_valid = 0;
+	  if (ret < 0)
+	    {
+	      backtrace_close (d, error_callback, data);
+	      return ret;
+	    }
+	}
+      else
+	{
+	  error_callback (data,
+			  "Could not open .gnu_debugaltlink", 0);
+	  /* Don't goto fail, but try continue without the info in the
+	     .gnu_debugaltlink.  */
+	}
+    }
+
+  if (debugaltlink_view_valid)
+    {
+      backtrace_release_view (state, &debugaltlink_view, error_callback, data);
+      debugaltlink_view_valid = 0;
+    }
+
   /* Read all the debug sections in a single view, since they are
      probably adjacent in the file.  We never release this view.  */
 
@@ -3199,6 +3282,8 @@ elf_add (struct backtrace_state *state, const char *filename, int descriptor,
     backtrace_release_view (state, &strtab_view, error_callback, data);
   if (debuglink_view_valid)
     backtrace_release_view (state, &debuglink_view, error_callback, data);
+  if (debugaltlink_view_valid)
+    backtrace_release_view (state, &debugaltlink_view, error_callback, data);
   if (buildid_view_valid)
     backtrace_release_view (state, &buildid_view, error_callback, data);
   if (debug_view_valid)
@@ -3269,7 +3354,7 @@ phdr_callback (struct dl_phdr_info *info, size_t size ATTRIBUTE_UNUSED,
 
   if (elf_add (pd->state, filename, descriptor, info->dlpi_addr,
 	       pd->error_callback, pd->data, &elf_fileline_fn, pd->found_sym,
-	       &found_dwarf, 0, 0))
+	       &found_dwarf, 0, 0, NULL, 0))
     {
       if (found_dwarf)
 	{
@@ -3297,7 +3382,7 @@ backtrace_initialize (struct backtrace_state *state, const char *filename,
   struct phdr_data pd;
 
   ret = elf_add (state, filename, descriptor, 0, error_callback, data,
-		 &elf_fileline_fn, &found_sym, &found_dwarf, 1, 0);
+		 &elf_fileline_fn, &found_sym, &found_dwarf, 1, 0, NULL, 0);
   if (!ret)
     return 0;
 
-- 
2.16.4


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