[PATCH] libdw, readelf: Handle GCC LTO .gnu.debuglto_ prefix.

[PATCH] libdw, readelf: Handle GCC LTO .gnu.debuglto_ prefix.

[Mark Wielaard]

GCC puts (partial) DWARF debuginfo into sections prefixed with
.gnu.debuglto_. Handle those sections as if they are normal .debug
sections (which they are). This allows showing the DWARF that gcc
puts into ET_REL files compiled with -flto.

Signed-off-by: Mark Wielaard <mark@klomp.org>
---
 libdw/ChangeLog         | 4 ++++
 libdw/dwarf_begin_elf.c | 4 ++++
 libebl/ChangeLog        | 5 +++++
 libebl/eblopenbackend.c | 4 +++-
 src/ChangeLog           | 4 ++++
 src/readelf.c           | 9 +++++++--
 6 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/libdw/ChangeLog b/libdw/ChangeLog
index 59f33f9e..39730fbc 100644
--- a/libdw/ChangeLog
+++ b/libdw/ChangeLog
@@ -1,3 +1,7 @@
+2020-04-17  Mark Wielaard  <mark@klomp.org>
+
+	* dwarf_begin_elf.c (check_section): Handle .gnu.debuglto_ prefix.
+
 2019-10-28  Aaron Merey  <amerey@redhat.com>
 
 	* Makefile.am (libdw_so_LDLIBS): Add -ldl for libdebuginfod.so dlopen.
diff --git a/libdw/dwarf_begin_elf.c b/libdw/dwarf_begin_elf.c
index 85343088..474ed138 100644
--- a/libdw/dwarf_begin_elf.c
+++ b/libdw/dwarf_begin_elf.c
@@ -137,6 +137,10 @@ check_section (Dwarf *result, size_t shstrndx, Elf_Scn *scn, bool inscngrp)
 	  gnu_compressed = true;
 	  break;
 	}
+      else if (scnlen > 14 /* .gnu.debuglto_ prefix. */
+	       && strncmp (scnname, ".gnu.debuglto_", 14) == 0
+	       && strcmp (&scnname[14], dwarf_scnnames[cnt]) == 0)
+	break;
     }
 
   if (cnt >= ndwarf_scnnames)
diff --git a/libebl/ChangeLog b/libebl/ChangeLog
index b3287310..90cf9728 100644
--- a/libebl/ChangeLog
+++ b/libebl/ChangeLog
@@ -1,3 +1,8 @@
+2020-04-17  Mark Wielaard  <mark@klomp.org>
+
+	* eblopenbackend.c (default_debugscn_p): Handle .gnu.debuglto_
+	prefix.
+
 2020-02-08  Mark Wielaard  <mark@klomp.org>
 
 	* eblsegmenttypename.c (ebl_segment_type_name): Handle
diff --git a/libebl/eblopenbackend.c b/libebl/eblopenbackend.c
index 210b47e8..4ebde45f 100644
--- a/libebl/eblopenbackend.c
+++ b/libebl/eblopenbackend.c
@@ -621,7 +621,9 @@ default_debugscn_p (const char *name)
   for (size_t cnt = 0; cnt < ndwarf_scn_names; ++cnt)
     if (strcmp (name, dwarf_scn_names[cnt]) == 0
 	|| (strncmp (name, ".zdebug", strlen (".zdebug")) == 0
-	    && strcmp (&name[2], &dwarf_scn_names[cnt][1]) == 0))
+	    && strcmp (&name[2], &dwarf_scn_names[cnt][1]) == 0)
+	|| (strncmp (name, ".gnu.debuglto_", strlen (".gnu.debuglto_")) == 0
+	    && strcmp (&name[14], dwarf_scn_names[cnt]) == 0))
       return true;
 
   return false;
diff --git a/src/ChangeLog b/src/ChangeLog
index e11fe79a..5d2d4254 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,7 @@
+2020-04-17  Mark Wielaard  <mark@klomp.org>
+
+	* readelf.c (print_debug): Check .gnu.debuglto_ prefix.
+
 2020-02-08  Mark Wielaard  <mark@klomp.org>
 
 	* elflint.c (check_program_header): Handle PT_GNU_PROPERTY.
diff --git a/src/readelf.c b/src/readelf.c
index cbb519d1..685d0b17 100644
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -11253,7 +11253,8 @@ print_debug (Dwfl_Module *dwflmod, Ebl *ebl, GElf_Ehdr *ehdr)
 	      if (strcmp (name, ".debug_info") == 0
 		  || strcmp (name, ".debug_info.dwo") == 0
 		  || strcmp (name, ".zdebug_info") == 0
-		  || strcmp (name, ".zdebug_info.dwo") == 0)
+		  || strcmp (name, ".zdebug_info.dwo") == 0
+		  || strcmp (name, ".gnu.debuglto_.debug_info") == 0)
 		{
 		  print_debug_info_section (dwflmod, ebl, ehdr,
 					    scn, shdr, dbg);
@@ -11339,7 +11340,11 @@ print_debug (Dwfl_Module *dwflmod, Ebl *ebl, GElf_Ehdr *ehdr)
 				  dbglen - 1) == 0
 		      && (scnlen == dbglen + 1
 			  || (scnlen == dbglen + 5
-			      && strstr (name, ".dwo") == name + dbglen + 1))))
+			      && strstr (name, ".dwo") == name + dbglen + 1)))
+		  || (scnlen > 14 /* .gnu.debuglto_ prefix. */
+		      && strncmp (name, ".gnu.debuglto_", 14) == 0
+		      && strcmp (&name[14], debug_sections[n].name) == 0)
+)
 		{
 		  if ((print_debug_sections | implicit_debug_sections)
 		      & debug_sections[n].bitmask)
-- 
2.18.2

Re: [PATCH] libdw, readelf: Handle GCC LTO .gnu.debuglto_ prefix.

[Mark Wielaard]

On Fri, Apr 17, 2020 at 11:35:37AM +0200, Mark Wielaard wrote:
> GCC puts (partial) DWARF debuginfo into sections prefixed with
> .gnu.debuglto_. Handle those sections as if they are normal .debug
> sections (which they are). This allows showing the DWARF that gcc
> puts into ET_REL files compiled with -flto.

I pushed this to master.