From: Mark Wielaard <mark@klomp.org>
To: Sonal Santan <sonals@xilinx.com>,
"elfutils-devel@sourceware.org" <elfutils-devel@sourceware.org>
Subject: Re: Working with ELF already loaded in memory
Date: Thu, 08 Jul 2021 17:02:01 +0200 [thread overview]
Message-ID: <19d95e93c233c8cf9abb1f065aba571d45657280.camel@klomp.org> (raw)
In-Reply-To: <BY5PR02MB6260DD7F130AA98334CCF886BB199@BY5PR02MB6260.namprd02.prod.outlook.com>
Hi Sinal,
On Thu, 2021-07-08 at 05:02 +0000, Sonal Santan via Elfutils-devel
wrote:
> Going through the libdw it appears that all APIs require either a
> file handle or a file name of the ELF object to create a session.
> Since we do not have access to the ELF file -- but rather the ELF
> file contents are already loaded in memory -- is there any other
> mechanism to create a session for extracting DWARF information using
> libdw?
Yes, if you just need the information already loaded into memory and
you know where the library is mapped you can use:
/* Create descriptor for memory region. */
extern Elf *elf_memory (char *__image, size_t __size);
You can then use that Elf handle to extract the information that has
been mapped in. Which often is not the actual debug information though.
If you have a Elf handle you can use:
/* Returns the build ID as found in a NT_GNU_BUILD_ID note from either
a SHT_NOTE section or from a PT_NOTE segment if the ELF file
doesn't contain any section headers. On success a pointer to the
build ID is written to *BUILDID_P, and the positive length of the
build ID is returned. Returns 0 if the ELF lacks a NT_GNU_BUILD_ID
note. Returns -1 in case of malformed data or other errors. */
extern ssize_t dwelf_elf_gnu_build_id (Elf *elf, const void **build_idp);
You can then use the build_id to lookup the debug information (file).
You can also use libdwfl (part of libdw) to do some of the above
automagically. See for example:
/* Call dwfl_report_module for each file mapped into the address space of PID.
Returns zero on success, -1 if dwfl_report_module failed,
or an errno code if opening the proc files failed. */
extern int dwfl_linux_proc_report (Dwfl *dwfl, pid_t pid);
The Dwfl will then be a representation of the modules (executable and
shared libraries) of that particular process. You can then iterate
through those modules using dwfl_getmodules and get a Dwarf handle
using dwfl_module_getdwarf (or for all with dwfl_getdwarf). libdw will
then try to extract that build-id from each module and try various
lookups to get the (separate on disk) debuginfo.
Hope that helps,
Mark
next prev parent reply other threads:[~2021-07-08 15:02 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-08 5:02 Sonal Santan
2021-07-08 15:02 ` Mark Wielaard [this message]
2021-07-09 5:34 ` Sonal Santan
2021-07-09 11:00 ` Mark Wielaard
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