[PATCH] libdwelf: New function dwelf_elf

Mark Wielaard

2018-10-21 23:47:40 UTC

This introduces a new function dwelf_elf_begin which creates a (read-only)
ELF handle from a possibly compressed file handle or a file that start
with a linux kernel header. This can be used in eu-readelf to (re)open a
(pure) ELF.

eu-readelf uses libdwfl to relocate addresses in the original file in
case it is ET_REL. But to show the "raw" data it might need to (re)open
the file. Which could fail if the file was compressed. And produced an
obscure error message: "cannot create EBL handle".

It currently wraps __libdw_open_file which makes error handling slight
tricky and needs duplicating the file handle.

Signed-off-by: Mark Wielaard <***@klomp.org>
---
libdw/ChangeLog | 4 +++
libdw/libdw.map | 5 ++++
libdwelf/ChangeLog | 8 +++++-
libdwelf/Makefile.am | 2 +-
libdwelf/dwelf_elf_begin.c | 61 +++++++++++++++++++++++++++++++++++++++++
libdwelf/libdwelf.h | 10 ++++++-
src/ChangeLog | 7 +++--
src/readelf.c | 8 ++++--
tests/ChangeLog | 6 ++++
tests/Makefile.am | 2 ++
tests/run-readelf-compressed.sh | 34 +++++++++++++++++++++++
11 files changed, 139 insertions(+), 8 deletions(-)
create mode 100644 libdwelf/dwelf_elf_begin.c
create mode 100755 tests/run-readelf-compressed.sh

diff --git a/libdw/ChangeLog b/libdw/ChangeLog
index ebe002c..e5d01c1 100644
--- a/libdw/ChangeLog
+++ b/libdw/ChangeLog
@@ -1,3 +1,7 @@
+2018-10-20 Mark Wielaard <***@klomp.org>
+
+ * libdw.map (ELFUTILS_0.175): New section. Add dwelf_elf_begin.
+
2018-09-13 Mark Wielaard <***@klomp.org>

* dwarf_begin_elf.c (check_section): Drop ehdr argument, add and
diff --git a/libdw/libdw.map b/libdw/libdw.map
index 3fef2ed..55482d5 100644
--- a/libdw/libdw.map
+++ b/libdw/libdw.map
@@ -356,3 +356,8 @@ ELFUTILS_0.173 {
global:
dwarf_next_lines;
} ELFUTILS_0.171;
+
+ELFUTILS_0.175 {
+ global:
+ dwelf_elf_begin;
+} ELFUTILS_0.173;
\ No newline at end of file
diff --git a/libdwelf/ChangeLog b/libdwelf/ChangeLog
index a332655..d26fe32 100644
--- a/libdwelf/ChangeLog
+++ b/libdwelf/ChangeLog
@@ -1,4 +1,10 @@
-2015-10-11 Akihiko Odaki <***@stu.hosei.ac.jp>
+2018-10-21 Mark Wielaard <***@klomp.org>
+
+ * libdwelf.h (dwelf_elf_begin): Add function declaration.
+ * dwelf_elf_begin.c: New file.
+ * Makefile.am (libdwelf_a_SOURCES): Add dwelf_elf_begin.c.
+
+2016-10-11 Akihiko Odaki <***@stu.hosei.ac.jp>

* dwelf_strtab.c: Remove sys/param.h include.
(MIN): Remove definition.
diff --git a/libdwelf/Makefile.am b/libdwelf/Makefile.am
index 7ca767a..a7933fd 100644
--- a/libdwelf/Makefile.am
+++ b/libdwelf/Makefile.am
@@ -41,7 +41,7 @@ noinst_HEADERS = libdwelfP.h

libdwelf_a_SOURCES = dwelf_elf_gnu_debuglink.c dwelf_dwarf_gnu_debugaltlink.c \
dwelf_elf_gnu_build_id.c dwelf_scn_gnu_compressed_size.c \
- dwelf_strtab.c
+ dwelf_strtab.c dwelf_elf_begin.c

libdwelf = $(libdw)

diff --git a/libdwelf/dwelf_elf_begin.c b/libdwelf/dwelf_elf_begin.c
new file mode 100644
index 0000000..43c3bc1
--- /dev/null
+++ b/libdwelf/dwelf_elf_begin.c
@@ -0,0 +1,61 @@
+/* Creates an ELF handle from a possibly compressed file descriptor.
+ Copyright (C) 2018 Red Hat, Inc.
+ This file is part of elfutils.
+
+ This file is free software; you can redistribute it and/or modify
+ it under the terms of either
+
+ * the GNU Lesser General Public License as published by the Free
+ Software Foundation; either version 3 of the License, or (at
+ your option) any later version
+
+ or
+
+ * the GNU General Public License as published by the Free
+ Software Foundation; either version 2 of the License, or (at
+ your option) any later version
+
+ or both in parallel, as here.
+
+ elfutils is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ General Public License for more details.
+
+ You should have received copies of the GNU General Public License and
+ the GNU Lesser General Public License along with this program. If
+ not, see <http://www.gnu.org/licenses/>. */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include "libdwelfP.h"
+#include "libdwflP.h"
+#include "libelfP.h"
+
+#include <unistd.h>
+
+Elf *
+dwelf_elf_begin (int fd)
+{
+ Elf *elf = NULL;
+ int elf_fd = dup (fd); /* __libdw_open_file will consume and close it. */
+ Dwfl_Error e = __libdw_open_file (&elf_fd, &elf, true, true);
+ if (elf != NULL && elf_kind (elf) != ELF_K_NONE)
+ return elf;
+
+ if (elf != NULL)
+ elf_end (elf);
+
+ if (e != DWFL_E_LIBELF)
+ {
+ /* Force a bad ELF error. */
+ char badelf[EI_NIDENT] = { };
+ Elf *belf = elf_memory (badelf, EI_NIDENT);
+ elf32_getehdr (belf);
+ elf_end (belf);
+ }
+
+ return NULL;
+}
diff --git a/libdwelf/libdwelf.h b/libdwelf/libdwelf.h
index 72089db..6d49184 100644
--- a/libdwelf/libdwelf.h
+++ b/libdwelf/libdwelf.h
@@ -1,5 +1,5 @@
/* Interfaces for libdwelf. DWARF ELF Low-level Functions.
- Copyright (C) 2014, 2015, 2016 Red Hat, Inc.
+ Copyright (C) 2014, 2015, 2016, 2018 Red Hat, Inc.
This file is part of elfutils.

This file is free software; you can redistribute it and/or modify
@@ -125,6 +125,14 @@ extern const char *dwelf_strent_str (Dwelf_Strent *se)
extern void dwelf_strtab_free (Dwelf_Strtab *st)
__nonnull_attribute__ (1);

+/* Creates a read-only Elf handle from the given file handle. The
+ file may be compressed and/or contain a linux kernel image header,
+ in which case it is eagerly decompressed in full and the Elf handle
+ is created as if created with elf_memory (). On error NULL is
+ returned. The Elf handle should be closed with elf_end (). The
+ file handle will not be closed. Does not return ELF_K_NONE handles. */
+extern Elf *dwelf_elf_begin (int fd);
+
#ifdef __cplusplus
}
#endif
diff --git a/src/ChangeLog b/src/ChangeLog
index 602312e..17d5ba6 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,7 @@
+2018-10-20 Mark Wielaard <***@klomp.org>
+
+ * readelf.c (process_elf_file): Use dwelf_elf_begin to open pure_elf.
+
2018-10-16 Mark Wielaard <***@klomp.org>

* readelf.c (print_debug_frame_section): Make sure readp is never
@@ -26,11 +30,10 @@

* findtextrel.c (process_file): Check that sh_entsize is not zero.

-2018-09-13 Mark Wielaard <***@klomp.org>
+2018-10-13 Mark Wielaard <***@klomp.org>

* readelf.c (print_debug_macro_section): Use elf_getdata. Print
decoded flag string.
-2018-09-13 Mark Wielaard <***@klomp.org>

2018-10-19 Mark Wielaard <***@klomp.org>

diff --git a/src/readelf.c b/src/readelf.c
index dfbb3d0..c4d8aa0 100644
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -905,7 +905,6 @@ process_elf_file (Dwfl_Module *dwflmod, int fd)

if (ehdr == NULL)
{
- elf_error:
error (0, 0, gettext ("cannot read ELF header: %s"), elf_errmsg (-1));
return;
}
@@ -948,7 +947,7 @@ process_elf_file (Dwfl_Module *dwflmod, int fd)
{
/* Read the file afresh. */
off_t aroff = elf_getaroff (elf);
- pure_elf = elf_begin (fd, ELF_C_READ_MMAP, NULL);
+ pure_elf = dwelf_elf_begin (fd);
if (aroff > 0)
{
/* Archive member. */
@@ -958,7 +957,10 @@ process_elf_file (Dwfl_Module *dwflmod, int fd)
pure_elf = armem;
}
if (pure_elf == NULL)
- goto elf_error;
+ {
+ error (0, 0, gettext ("cannot read ELF: %s"), elf_errmsg (-1));
+ return;
+ }
pure_ebl = ebl_openbackend (pure_elf);
if (pure_ebl == NULL)
goto ebl_error;
diff --git a/tests/ChangeLog b/tests/ChangeLog
index 751a081..e64a8b5 100644
--- a/tests/ChangeLog
+++ b/tests/ChangeLog
@@ -1,3 +1,9 @@
+2018-10-20 Mark Wielaard <***@klomp.org>
+
+ * run-readelf-compressed.sh: New test.
+ * Makefile.am (TESTS): Add run-readelf-compressed.sh.
+ (EXTRA_DIST): Likewise.
+
2018-10-12 Mark Wielaard <***@klomp.org>

* run-readelf-zdebug.sh: Adjust flags output.
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 15b429b..165a414 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -100,6 +100,7 @@ TESTS = run-arextract.sh run-arsymtest.sh run-ar.sh newfile test-nlist \
run-find-prologues.sh run-allregs.sh run-addrcfi.sh \
run-dwarfcfi.sh \
run-nm-self.sh run-readelf-self.sh run-readelf-info-plus.sh \
+ run-readelf-compressed.sh \
run-readelf-const-values.sh \
run-varlocs-self.sh run-exprlocs-self.sh \
run-readelf-test1.sh run-readelf-test2.sh run-readelf-test3.sh \
@@ -215,6 +216,7 @@ EXTRA_DIST = run-arextract.sh run-arsymtest.sh run-ar.sh \
run-ranlib-test3.sh run-ranlib-test4.sh \
run-addrscopes.sh run-strings-test.sh run-funcscopes.sh \
run-nm-self.sh run-readelf-self.sh run-readelf-info-plus.sh \
+ run-readelf-compressed.sh \
run-readelf-const-values.sh testfile-const-values.debug.bz2 \
run-addrcfi.sh run-dwarfcfi.sh \
testfile11-debugframe.bz2 testfile12-debugframe.bz2 \
diff --git a/tests/run-readelf-compressed.sh b/tests/run-readelf-compressed.sh
new file mode 100755
index 0000000..a2a04a2
--- /dev/null
+++ b/tests/run-readelf-compressed.sh
@@ -0,0 +1,34 @@
+#! /bin/sh
+# Copyright (C) 2018 Red Hat, Inc.
+# This file is part of elfutils.
+#
+# This file is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# elfutils is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+. $srcdir/test-subr.sh
+
+# See run-strip-reloc.sh
+testfiles hello_i386.ko
+
+tempfiles hello_i386.ko.bz2 readelf.out.1 readelf.out.2
+
+testrun ${abs_top_builddir}/src/readelf -a hello_i386.ko > readelf.out.1
+bzip2 hello_i386.ko
+testrun ${abs_top_builddir}/src/readelf -a hello_i386.ko.bz2 > readelf.out.2
+
+diff -u readelf.out.1 readelf.out.2
+if [ $? != 0 ]; then
+ exit 1;
+fi
+
+exit 0

--
1.8.3.1