gdb: Incorrect stack unwinding if compressed debug info is used

[Vladimir Simonov <sv@sw.ru>]

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Hi all,

Environment: gdb-weekly-CVS-7.2.50.20110125, binutils 2.21, gcc 4.4.3, Linux, i686,
  32 bit kernel 2.6.32.

If I create -Od -g3 executable with -Wl,compressed-debug-sections=zlib
using gold linker or compress debug-info via objcopy I have problems with
local variables and bacttraces in gdb.
Something like this:
gdb: bt
....
#11 0xb2356a74 in Core::WorkerImpl::WorkerThread (this=Could not find
the frame base for "Core::WorkerImpl::WorkerThread()".
)
....

I've spend some time and, looks like, found the problem. It is in
dwarf2_symbol_mark_computed function (dwarf2read.c). Check
"DW_UNSND (attr) < dwarf2_per_objfile->loc.size"
is incorrect if compressed section is used. In this case
loc.size contains compressed section size, not decompressed one.
It happens if the section has not been read via dwarf2_read_section yet.
But dwarf2_locate_sections has been done.
As result symbols not passed above verification are left with
size==0 and data==NULL after dwarf2_symbol_mark_computed function.

The patch idea is to introduce uncompressed_size field in
struct dwarf2_section_info. And fill it in dwarf2_locate_sections.
Check in dwarf2_symbol_mark_computed function takes into
account uncompressed_size. The patch is quite large cause I
try to avoid code duplication with zlib_decompress section.

Any comments are welcome

Best regards
Vladimir Simonov

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diff -ruN gdb-weekly-CVS-7.2.50.20110125/gdb/dwarf2read.c gdb-7.2/gdb/dwarf2read.c
--- gdb-weekly-CVS-7.2.50.20110125/gdb/dwarf2read.c	2011-01-12 19:16:20.000000000 +0300
+++ ./gdb/dwarf2read.c	2011-01-31 18:03:37.072688100 +0300
@@ -136,6 +136,7 @@
   int was_mmapped;
   /* True if we have tried to read this section.  */
   int readin;
+  bfd_size_type uncompressed_size;
 };
 
 /* All offsets in the index are of this type.  It must be
@@ -1357,6 +1358,59 @@
 		  && strcmp (section_name + 2, name) == 0)));
 }
 
+static int
+is_compressed_section_name (const char *section_name)
+{
+  return (section_name[0] == '.' && section_name[1] == 'z');
+}
+
+static int
+parse_zlib_section_header (bfd_byte *compressed_buffer, bfd_size_type *size)
+{
+  bfd_size_type uncompressed_size;
+
+ /* Read the zlib header. In this case, it should be "ZLIB" followed
+     by the uncompressed section size, 8 bytes in big-endian order.  */
+  if (strncmp (compressed_buffer, "ZLIB", 4) != 0)
+    return FALSE;
+  uncompressed_size = compressed_buffer[4]; uncompressed_size <<= 8;
+  uncompressed_size += compressed_buffer[5]; uncompressed_size <<= 8;
+  uncompressed_size += compressed_buffer[6]; uncompressed_size <<= 8;
+  uncompressed_size += compressed_buffer[7]; uncompressed_size <<= 8;
+  uncompressed_size += compressed_buffer[8]; uncompressed_size <<= 8;
+  uncompressed_size += compressed_buffer[9]; uncompressed_size <<= 8;
+  uncompressed_size += compressed_buffer[10]; uncompressed_size <<= 8;
+  uncompressed_size += compressed_buffer[11];
+  *size = uncompressed_size;
+  return TRUE;
+}
+
+static int
+read_uncompressed_size (bfd *abfd, asection *sec, bfd_size_type *size)
+{
+  bfd_byte compressed_buffer [12];
+  bfd_size_type uncompressed_size;
+
+  if (sec->size < 12 || !bfd_get_section_contents (abfd, sec,
+					compressed_buffer, 0, 12))
+    return FALSE;
+  return parse_zlib_section_header (compressed_buffer, size);
+}
+
+static void
+fill_dwarf2_section_info (struct dwarf2_section_info* info,
+			  bfd *abfd, asection *sectp)
+{
+  bfd_size_type size;
+
+  info->asection = sectp;
+  info->size = bfd_get_section_size (sectp);
+  info->uncompressed_size = 0;
+  if (!is_compressed_section_name (sectp->name))
+    return;
+  read_uncompressed_size (abfd, sectp, &info->uncompressed_size);
+}
+
 /* This function is mapped across the sections and remembers the
    offset and size of each of the debugging sections we are interested
    in.  */
@@ -1366,38 +1420,31 @@
 {
   if (section_is_p (sectp->name, INFO_SECTION))
     {
-      dwarf2_per_objfile->info.asection = sectp;
-      dwarf2_per_objfile->info.size = bfd_get_section_size (sectp);
+      fill_dwarf2_section_info(&dwarf2_per_objfile->info, abfd, sectp);
     }
   else if (section_is_p (sectp->name, ABBREV_SECTION))
     {
-      dwarf2_per_objfile->abbrev.asection = sectp;
-      dwarf2_per_objfile->abbrev.size = bfd_get_section_size (sectp);
+      fill_dwarf2_section_info(&dwarf2_per_objfile->abbrev, abfd, sectp);
     }
   else if (section_is_p (sectp->name, LINE_SECTION))
     {
-      dwarf2_per_objfile->line.asection = sectp;
-      dwarf2_per_objfile->line.size = bfd_get_section_size (sectp);
+      fill_dwarf2_section_info(&dwarf2_per_objfile->line, abfd, sectp);
     }
   else if (section_is_p (sectp->name, LOC_SECTION))
     {
-      dwarf2_per_objfile->loc.asection = sectp;
-      dwarf2_per_objfile->loc.size = bfd_get_section_size (sectp);
+      fill_dwarf2_section_info(&dwarf2_per_objfile->loc, abfd, sectp);
     }
   else if (section_is_p (sectp->name, MACINFO_SECTION))
     {
-      dwarf2_per_objfile->macinfo.asection = sectp;
-      dwarf2_per_objfile->macinfo.size = bfd_get_section_size (sectp);
+      fill_dwarf2_section_info(&dwarf2_per_objfile->macinfo, abfd, sectp);
     }
   else if (section_is_p (sectp->name, STR_SECTION))
     {
-      dwarf2_per_objfile->str.asection = sectp;
-      dwarf2_per_objfile->str.size = bfd_get_section_size (sectp);
+      fill_dwarf2_section_info(&dwarf2_per_objfile->str, abfd, sectp);
     }
   else if (section_is_p (sectp->name, FRAME_SECTION))
     {
-      dwarf2_per_objfile->frame.asection = sectp;
-      dwarf2_per_objfile->frame.size = bfd_get_section_size (sectp);
+      fill_dwarf2_section_info(&dwarf2_per_objfile->frame, abfd, sectp);
     }
   else if (section_is_p (sectp->name, EH_FRAME_SECTION))
     {
@@ -1405,24 +1452,20 @@
 
       if (aflag & SEC_HAS_CONTENTS)
         {
-	  dwarf2_per_objfile->eh_frame.asection = sectp;
-          dwarf2_per_objfile->eh_frame.size = bfd_get_section_size (sectp);
+          fill_dwarf2_section_info(&dwarf2_per_objfile->eh_frame, abfd, sectp);
         }
     }
   else if (section_is_p (sectp->name, RANGES_SECTION))
     {
-      dwarf2_per_objfile->ranges.asection = sectp;
-      dwarf2_per_objfile->ranges.size = bfd_get_section_size (sectp);
+      fill_dwarf2_section_info(&dwarf2_per_objfile->ranges, abfd, sectp);
     }
   else if (section_is_p (sectp->name, TYPES_SECTION))
     {
-      dwarf2_per_objfile->types.asection = sectp;
-      dwarf2_per_objfile->types.size = bfd_get_section_size (sectp);
+      fill_dwarf2_section_info(&dwarf2_per_objfile->types, abfd, sectp);
     }
   else if (section_is_p (sectp->name, GDB_INDEX_SECTION))
     {
-      dwarf2_per_objfile->gdb_index.asection = sectp;
-      dwarf2_per_objfile->gdb_index.size = bfd_get_section_size (sectp);
+      fill_dwarf2_section_info(&dwarf2_per_objfile->gdb_index, abfd, sectp);
     }
 
   if ((bfd_get_section_flags (abfd, sectp) & SEC_LOAD)
@@ -1435,7 +1478,7 @@
 
 static void
 zlib_decompress_section (struct objfile *objfile, asection *sectp,
-                         gdb_byte **outbuf, bfd_size_type *outsize)
+                         gdb_byte **outbuf)
 {
   bfd *abfd = objfile->obfd;
 #ifndef HAVE_ZLIB_H
@@ -1452,26 +1495,19 @@
   int rc;
   int header_size = 12;
 
+  if (compressed_size < header_size)
+    error (_("Dwarf Error: Too small DWARF ZLIB header from '%s'"),
+           bfd_get_filename (abfd));
+
   if (bfd_seek (abfd, sectp->filepos, SEEK_SET) != 0
       || bfd_bread (compressed_buffer,
 		    compressed_size, abfd) != compressed_size)
     error (_("Dwarf Error: Can't read DWARF data from '%s'"),
            bfd_get_filename (abfd));
 
-  /* Read the zlib header.  In this case, it should be "ZLIB" followed
-     by the uncompressed section size, 8 bytes in big-endian order.  */
-  if (compressed_size < header_size
-      || strncmp (compressed_buffer, "ZLIB", 4) != 0)
+  if (!parse_zlib_section_header (compressed_buffer, &uncompressed_size))
     error (_("Dwarf Error: Corrupt DWARF ZLIB header from '%s'"),
            bfd_get_filename (abfd));
-  uncompressed_size = compressed_buffer[4]; uncompressed_size <<= 8;
-  uncompressed_size += compressed_buffer[5]; uncompressed_size <<= 8;
-  uncompressed_size += compressed_buffer[6]; uncompressed_size <<= 8;
-  uncompressed_size += compressed_buffer[7]; uncompressed_size <<= 8;
-  uncompressed_size += compressed_buffer[8]; uncompressed_size <<= 8;
-  uncompressed_size += compressed_buffer[9]; uncompressed_size <<= 8;
-  uncompressed_size += compressed_buffer[10]; uncompressed_size <<= 8;
-  uncompressed_size += compressed_buffer[11];
 
   /* It is possible the section consists of several compressed
      buffers concatenated together, so we uncompress in a loop.  */
@@ -1505,7 +1541,6 @@
 
   do_cleanups (cleanup);
   *outbuf = uncompressed_buffer;
-  *outsize = uncompressed_size;
 #endif
 }
 
@@ -1519,29 +1554,23 @@
   bfd *abfd = objfile->obfd;
   asection *sectp = info->asection;
   gdb_byte *buf, *retbuf;
-  unsigned char header[4];
 
   if (info->readin)
     return;
   info->buffer = NULL;
   info->was_mmapped = 0;
   info->readin = 1;
+  info->uncompressed_size = 0;
 
   if (info->asection == NULL || info->size == 0)
     return;
 
-  /* Check if the file has a 4-byte header indicating compression.  */
-  if (info->size > sizeof (header)
-      && bfd_seek (abfd, sectp->filepos, SEEK_SET) == 0
-      && bfd_bread (header, sizeof (header), abfd) == sizeof (header))
+  /* Check if the file has a 12-byte header indicating compression.  */
+  if (read_uncompressed_size (abfd, sectp, &info->uncompressed_size))
     {
-      /* Upon decompression, update the buffer and its size.  */
-      if (strncmp (header, "ZLIB", sizeof (header)) == 0)
-        {
-          zlib_decompress_section (objfile, sectp, &info->buffer,
-				   &info->size);
-          return;
-        }
+      zlib_decompress_section (objfile, sectp, &info->buffer);
+      info->size = info->uncompressed_size;
+      return;
     }
 
 #ifdef HAVE_MMAP
@@ -14356,6 +14385,14 @@
   baton->base_address = cu->base_address;
 }
 
+static int
+check_attr_location (struct dwarf2_section_info *info, struct attribute *attr)
+{
+  if (info->uncompressed_size)
+    return DW_UNSND (attr) < info->uncompressed_size;
+  return DW_UNSND (attr) < info->size;
+}
+
 static void
 dwarf2_symbol_mark_computed (struct attribute *attr, struct symbol *sym,
 			     struct dwarf2_cu *cu)
@@ -14364,7 +14401,7 @@
       /* ".debug_loc" may not exist at all, or the offset may be outside
 	 the section.  If so, fall through to the complaint in the
 	 other branch.  */
-      && DW_UNSND (attr) < dwarf2_per_objfile->loc.size)
+      && check_attr_location (&dwarf2_per_objfile->loc, attr))
     {
       struct dwarf2_loclist_baton *baton;