2012-11-26 Alexander Larsson <alexl@redhat.com>

	    Jan Kratochvil  <jan.kratochvil@redhat.com>
	    Tom Tromey  <tromey@redhat.com>

	* NEWS: Mention mini debuginfo feature.
	* minidebug.c: New file.
	* configure.ac: Check for lzma.
	* configure, config.in: Rebuild.
	* Makefile.in (LIBLZMA): New variable.
	(CLIBS): Include LIBLZMA.
	(SFILES): Mention minidebug.c.
	(COMMON_OBS): Mention minidebug.o.
	* symfile.c (read_symbols): New function.
	(syms_from_objfile, reread_symbols): Call it.
	* symfile.h (find_separate_debug_file_in_section): Declare.
doc
	* gdb.texinfo (MiniDebugInfo): New node.
	(GDB Files): Update.
testsuite
	* gdb.base/gnu-debugdata.exp: New file.
	* gdb.base/gnu-debugdata.c: New file.
	* lib/gdb.exp (gdb_file_cmd): Handle LZMA warning.
	(gdb_unload): Return 0 on success.

2 files changed, 55 insertions, 0 deletions

diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 8fda5d5..b594764 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,8 @@
+2012-11-26  Tom Tromey  <tromey@redhat.com>
+
+	* gdb.texinfo (MiniDebugInfo): New node.
+	(GDB Files): Update.
+
 2012-11-16  Doug Evans  <dje@google.com>
 
 	* gdb.texinfo (System-wide configuration): If the system-wide init
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 80148f7..afe3845 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -15865,6 +15865,7 @@ program.  To debug a core dump of a previous run, you must also tell
 @menu
 * Files::                       Commands to specify files
 * Separate Debug Files::        Debugging information in separate files
+* MiniDebugInfo::               Debugging information in a special section
 * Index Files::                 Index files speed up GDB
 * Symbol Errors::               Errors reading symbol files
 * Data Files::                  GDB data files
@@ -16790,6 +16791,55 @@ gnu_debuglink_crc32 (unsigned long crc,
 @noindent
 This computation does not apply to the ``build ID'' method.
 
+@node MiniDebugInfo
+@section Debugging information in a special section
+@cindex separate debug sections
+@cindex @samp{.gnu_debugdata} section
+
+Some systems ship pre-built executables and libraries that have a
+special @samp{.gnu_debugdata} section.  This feature is called
+@dfn{MiniDebugInfo}.  This section holds an LZMA-compressed object and
+is used to supply extra symbols for backtraces.
+
+The intent of this section is to provide extra minimal debugging
+information for use in simple backtraces.  It is not intended to be a
+replacement for full separate debugging information (@pxref{Separate
+Debug Files}).  The example below shows the intended use; however,
+@value{GDBN} does not currently put restrictions on what sort of
+debugging information might be included in the section.
+
+@value{GDBN} has support for this extension.  If the section exists,
+then it is used provided that no other source of debugging information
+can be found, and that @value{GDBN} was configured with LZMA support.
+
+This section can be easily created using @command{objcopy} and other
+standard utilities:
+
+@smallexample
+# Extract the dynamic symbols from the main binary, there is no need
+# to also have these in the normal symbol table
+nm -D @var{binary} --format=posix --defined-only \
+  | awk '@{ print $1 @}' | sort > dynsyms
+
+# Extract all the text (i.e. function) symbols from the debuginfo .
+nm @var{binary} --format=posix --defined-only \
+  | awk '@{ if ($2 == "T" || $2 == "t") print $1 @}' \
+  | sort > funcsyms
+
+# Keep all the function symbols not already in the dynamic symbol
+# table.
+comm -13 dynsyms funcsyms > keep_symbols
+
+# Copy the full debuginfo, keeping only a minimal set of symbols and
+# removing some unnecessary sections.
+objcopy -S --remove-section .gdb_index --remove-section .comment \
+  --keep-symbols=keep_symbols @var{binary} mini_debuginfo
+
+# Inject the compressed data into the .gnu_debugdata section of the
+# original binary.
+xz mini_debuginfo
+objcopy --add-section .gnu_debugdata=mini_debuginfo.xz @var{binary}
+@end smallexample
 
 @node Index Files
 @section Index Files Speed Up @value{GDBN}