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[PATCH 10/10] libdwfl: Document core memory and remote memory ELF shdrs reading.
- From: Mark Wielaard <mark at klomp dot org>
- To: elfutils-devel at sourceware dot org
- Cc: Mark Wielaard <mark at klomp dot org>
- Date: Fri, 14 Sep 2018 01:01:40 +0200
- Subject: [PATCH 10/10] libdwfl: Document core memory and remote memory ELF shdrs reading.
- References: <1536879700-30439-1-git-send-email-mark@klomp.org>
There are two places, dwfl_segment_report_module and elf_from_remote_memory
in libdwfl where we use the Ehdr e_shnum directly. Document why this is fine.
Getting the shdrs in those two places is really just a nice bonus and if there
are more than 0xff00 then it is unlikely we will get them all anyway.
Signed-off-by: Mark Wielaard <mark@klomp.org>
---
libdwfl/ChangeLog | 6 ++++++
libdwfl/dwfl_segment_report_module.c | 6 ++++++
libdwfl/elf-from-memory.c | 6 ++++++
3 files changed, 18 insertions(+)
diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index 15d7511..5e9b986 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,3 +1,9 @@
+2018-09-13 Mark Wielaard <mark@klomp.org>
+
+ * dwfl_segment_report_module.c (dwfl_segment_report_module):
+ Document why we use e_shnum directly.
+ * elf-from-memory.c (elf_from_remote_memory): Likewise.
+
2018-07-17 Ulf Hermann <ulf.hermann@qt.io>
* linux-pid-attach.c: Include sys/uio.h only on linux.
diff --git a/libdwfl/dwfl_segment_report_module.c b/libdwfl/dwfl_segment_report_module.c
index 207a257..36e5c82 100644
--- a/libdwfl/dwfl_segment_report_module.c
+++ b/libdwfl/dwfl_segment_report_module.c
@@ -367,6 +367,11 @@ dwfl_segment_report_module (Dwfl *dwfl, int ndx, const char *name,
phentsize = ehdr.e32.e_phentsize;
if (phentsize != sizeof (Elf32_Phdr))
return finish ();
+ /* NOTE if the number of sections is > 0xff00 then e_shnum
+ is zero and the actual number would come from the section
+ zero sh_size field. We ignore this here because getting shdrs
+ is just a nice bonus (see below in consider_phdr PT_LOAD
+ where we trim the last segment). */
shdrs_end = ehdr.e32.e_shoff + ehdr.e32.e_shnum * ehdr.e32.e_shentsize;
break;
@@ -380,6 +385,7 @@ dwfl_segment_report_module (Dwfl *dwfl, int ndx, const char *name,
phentsize = ehdr.e64.e_phentsize;
if (phentsize != sizeof (Elf64_Phdr))
return finish ();
+ /* See the NOTE above for shdrs_end and ehdr.e32.e_shnum. */
shdrs_end = ehdr.e64.e_shoff + ehdr.e64.e_shnum * ehdr.e64.e_shentsize;
break;
diff --git a/libdwfl/elf-from-memory.c b/libdwfl/elf-from-memory.c
index 12a0a1b..c54c1b9 100644
--- a/libdwfl/elf-from-memory.c
+++ b/libdwfl/elf-from-memory.c
@@ -139,6 +139,11 @@ elf_from_remote_memory (GElf_Addr ehdr_vma,
phentsize = ehdr.e32.e_phentsize;
if (phentsize != sizeof (Elf32_Phdr) || phnum == 0)
goto bad_elf;
+ /* NOTE if the number of sections is > 0xff00 then e_shnum
+ is zero and the actual number would come from the section
+ zero sh_size field. We ignore this here because getting shdrs
+ is just a nice bonus (see below where we trim the last phdrs
+ PT_LOAD segment). */
shdrs_end = ehdr.e32.e_shoff + ehdr.e32.e_shnum * ehdr.e32.e_shentsize;
break;
@@ -151,6 +156,7 @@ elf_from_remote_memory (GElf_Addr ehdr_vma,
phentsize = ehdr.e64.e_phentsize;
if (phentsize != sizeof (Elf64_Phdr) || phnum == 0)
goto bad_elf;
+ /* See the NOTE above for shdrs_end and ehdr.e32.e_shnum. */
shdrs_end = ehdr.e64.e_shoff + ehdr.e64.e_shnum * ehdr.e64.e_shentsize;
break;
--
1.8.3.1