patches/0001-libdwfl-Make-dwfl_report_offline_memory-work-with-EL.patch

From 94cb85c3cbc59811de11869d1c1ce4f9bdb7f67c Mon Sep 17 00:00:00 2001
From: Aleksei Vetrov <vvvvvv@google.com>
Date: Thu, 11 Jul 2024 19:29:32 +0000
Subject: [PATCH] libdwfl: Make dwfl_report_offline_memory work with
 ELF_C_READ_MMAP
To: elfutils-devel@sourceware.org
Cc: kernel-team@android.com,
    maennich@google.com,
    vvvvvv@google.com

elf_memory open mode recently changed from ELF_C_READ to
ELF_C_READ_MMAP. This broken dwfl_report_offline_memory that changes
mode to ELF_C_READ_MMAP_PRIVATE to be compatible with subsequent
elf_begin on embedded ELF files.

The proper implementation of dwfl_report_offline_memory doesn't change
open mode and subsequent elf_begin invocations simply use cmd from the
reference Elf*.

Add tests to exercise Elf* to trigger the bug caused by incorrect cmd
set to Elf*.

	  * libdwfl/offline.c (process_archive): Use archive->cmd
	  instead of hardcoded ELF_C_READ_MMAP_PRIVATE.
	  * libdwfl/open.c (libdw_open_elf): Use elf->cmd instead of
	  hardcoded ELF_C_READ_MMAP_PRIVATE.
	  (__libdw_open_elf_memory): Don't override (*elfp)->cmd.
	  * tests/Makefile.am (dwfl_report_offline_memory): Add libelf
	  as dependency.
	  * tests/dwfl-report-offline-memory.c: Add count_sections to
	  exercise Elf* from dwfl_report_offline_memory.
	  * tests/run-dwfl-report-offline-memory.sh: Add expected number
	  of sections to test invocations.

Signed-off-by: Aleksei Vetrov <vvvvvv@google.com>
---
 libdwfl/offline.c                       |  5 ++--
 libdwfl/open.c                          |  4 +---
 tests/Makefile.am                       |  2 +-
 tests/dwfl-report-offline-memory.c      | 32 ++++++++++++++++++++++---
 tests/run-dwfl-report-offline-memory.sh |  6 ++---
 5 files changed, 37 insertions(+), 12 deletions(-)

diff --git a/libdwfl/offline.c b/libdwfl/offline.c
index e9ab0cc1..24e9e180 100644
--- a/libdwfl/offline.c
+++ b/libdwfl/offline.c
@@ -32,6 +32,7 @@
 # include <config.h>
 #endif
 
+#include "libelfP.h"
 #include "libdwflP.h"
 #include <fcntl.h>
 
@@ -254,7 +255,7 @@ process_archive (Dwfl *dwfl, const char *name, const char *file_name, int fd,
 {
   Dwfl_Module *mod = NULL;
   /* elf_begin supports opening archives even with fd == -1 passed.  */
-  Elf *member = elf_begin (fd, ELF_C_READ_MMAP_PRIVATE, archive);
+  Elf *member = elf_begin (fd, archive->cmd, archive);
   if (unlikely (member == NULL)) /* Empty archive.  */
     {
       __libdwfl_seterrno (DWFL_E_BADELF);
@@ -263,7 +264,7 @@ process_archive (Dwfl *dwfl, const char *name, const char *file_name, int fd,
 
   while (process_archive_member (dwfl, name, file_name, predicate,
 				 fd, member, &mod) != ELF_C_NULL)
-    member = elf_begin (fd, ELF_C_READ_MMAP_PRIVATE, archive);
+    member = elf_begin (fd, archive->cmd, archive);
 
   /* We can drop the archive Elf handle even if we're still using members
      in live modules.  When the last module's elf_end on a member returns
diff --git a/libdwfl/open.c b/libdwfl/open.c
index d0f357ed..43b29fa9 100644
--- a/libdwfl/open.c
+++ b/libdwfl/open.c
@@ -151,7 +151,7 @@ libdw_open_elf (int *fdp, Elf **elfp, bool close_on_fail, bool archive_ok,
 	  elf->state.ar.elf_ar_hdr.ar_name = "libdwfl is faking you out";
 	  elf->state.ar.elf_ar_hdr.ar_size = elf->maximum_size - offset;
 	  elf->state.ar.offset = offset - sizeof (struct ar_hdr);
-	  Elf *subelf = elf_begin (-1, ELF_C_READ_MMAP_PRIVATE, elf);
+	  Elf *subelf = elf_begin (-1, elf->cmd, elf);
 	  elf->kind = ELF_K_NONE;
 	  if (unlikely (subelf == NULL))
 	    error = DWFL_E_LIBELF;
@@ -215,8 +215,6 @@ __libdw_open_elf_memory (char *data, size_t size, Elf **elfp, bool archive_ok)
     {
       return DWFL_E_LIBELF;
     }
-  /* Allow using this ELF as reference for subsequent elf_begin calls.  */
-  (*elfp)->cmd = ELF_C_READ_MMAP_PRIVATE;
   return libdw_open_elf (&fd, elfp, false, archive_ok, true, false, true);
 }
 
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 77f9b90d..cfed54b7 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -792,7 +792,7 @@ test_elf_cntl_gelf_getshdr_LDADD = $(libelf)
 dwflsyms_LDADD = $(libdw) $(libelf) $(argp_LDADD)
 dwfllines_LDADD = $(libeu) $(libdw) $(libelf) $(argp_LDADD)
 dwfl_report_elf_align_LDADD = $(libeu) $(libdw)
-dwfl_report_offline_memory_LDADD = $(libeu) $(libdw)
+dwfl_report_offline_memory_LDADD = $(libeu) $(libdw) $(libelf)
 dwfl_report_segment_contiguous_LDADD = $(libdw) $(libebl) $(libelf)
 varlocs_LDADD = $(libeu) $(libdw) $(libelf) $(argp_LDADD)
 backtrace_LDADD = $(libeu) $(libdw) $(libelf) $(argp_LDADD)
diff --git a/tests/dwfl-report-offline-memory.c b/tests/dwfl-report-offline-memory.c
index b3b4d9bd..3ecb66b9 100644
--- a/tests/dwfl-report-offline-memory.c
+++ b/tests/dwfl-report-offline-memory.c
@@ -18,14 +18,19 @@
 #include <config.h>
 
 #include <assert.h>
+#include <errno.h>
+#include <error.h>
 #include <fcntl.h>
 #include <locale.h>
 #include <stdio.h>
 #include <stdio_ext.h>
 #include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
+
 #include ELFUTILS_HEADER(dwfl)
-#include "system.h"
+#include ELFUTILS_HEADER(elf)
+#include <gelf.h>
 
 
 static const Dwfl_Callbacks offline_callbacks =
@@ -45,6 +50,20 @@ count_modules (Dwfl_Module *mod __attribute__ ((unused)),
   return DWARF_CB_OK;
 }
 
+static int
+count_sections (Elf *elf)
+{
+  int result = 0;
+  Elf_Scn *section = NULL;
+  GElf_Shdr header;
+  while ((section = elf_nextscn (elf, section)) != NULL)
+    {
+      assert (gelf_getshdr (section, &header) != NULL);
+      result += 1;
+    }
+  return result;
+}
+
 int
 main (int argc, char **argv)
 {
@@ -54,10 +73,11 @@ main (int argc, char **argv)
   /* Set locale.  */
   (void) setlocale (LC_ALL, "");
 
-  if (argc != 3)
+  if (argc != 4)
     error (-1, 0,
 	   "usage: dwfl_report_offline_memory [filename] "
-	   "[expected number of modules]");
+	   "[expected number of modules] "
+	   "[expected number of sections]");
 
   const char *fname = argv[1];
   int fd = open (fname, O_RDONLY);
@@ -100,6 +120,12 @@ main (int argc, char **argv)
   assert (endptr && !*endptr);
   assert (number_of_modules == expected_number_of_modules);
 
+  GElf_Addr loadbase = 0;
+  Elf *elf = dwfl_module_getelf (mod, &loadbase);
+  int number_of_sections = count_sections (elf);
+  int expected_number_of_sections = atoi (argv[3]);
+  assert (number_of_sections == expected_number_of_sections);
+
   dwfl_end (dwfl);
   free (data);
 
diff --git a/tests/run-dwfl-report-offline-memory.sh b/tests/run-dwfl-report-offline-memory.sh
index 85f43f53..84c7f999 100755
--- a/tests/run-dwfl-report-offline-memory.sh
+++ b/tests/run-dwfl-report-offline-memory.sh
@@ -26,8 +26,8 @@ testfiles testarchive64.a
 # bzip2 -zf test-ar-duplicates.a
 testfiles test-ar-duplicates.a
 
-testrun ${abs_builddir}/dwfl-report-offline-memory ./testfile-dwfl-report-elf-align-shlib.so 1
-testrun ${abs_builddir}/dwfl-report-offline-memory ./testarchive64.a 3
-testrun ${abs_builddir}/dwfl-report-offline-memory ./test-ar-duplicates.a 1
+testrun ${abs_builddir}/dwfl-report-offline-memory ./testfile-dwfl-report-elf-align-shlib.so 1 24
+testrun ${abs_builddir}/dwfl-report-offline-memory ./testarchive64.a 3 10
+testrun ${abs_builddir}/dwfl-report-offline-memory ./test-ar-duplicates.a 1 7
 
 exit 0
-- 
2.45.2.993.g49e7a77208-goog