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Re: vdso handling
- From: Doug Evans <dje at google dot com>
- To: "Metzger, Markus T" <markus dot t dot metzger at intel dot com>, "gdb at sourceware dot org" <gdb at sourceware dot org>, "binutils at sourceware dot org" <binutils at sourceware dot org>
- Date: Wed, 12 Mar 2014 10:34:36 -0700
- Subject: Re: vdso handling
- Authentication-results: sourceware.org; auth=none
- References: <A78C989F6D9628469189715575E55B230AA884EB at IRSMSX104 dot ger dot corp dot intel dot com> <20140312071701 dot GW26922 at bubble dot grove dot modra dot org>
On Wed, Mar 12, 2014 at 12:17 AM, Alan Modra <email@example.com> wrote:
> On Mon, Mar 10, 2014 at 01:04:33PM +0000, Metzger, Markus T wrote:
>> I noticed that the BFD created for the VDSO (system-provided in-memory
>> DSO) does not contain any BFD sections. Is this intentional? Or has
>> there just been no need for them?
>> The vdso is processed in symbol_file_add_from_memory at
>> gdb/symfile-mem.c:84. It calls bfd_from_remote_memory to create a BFD
>> for the vdso and then processes it.
> The underlying cause is that you're trying to debug an ELF binary that
> only contains the execution view. The linking view (of which the
> sections are a part) is not loaded, so bfd_from_remote_memory does not
> have this information. See elfcode.h bfd_from_remote_memory.
> You can see similar breakage of gdb and binutils if you zap e_shoff,
> e_shnum, and e_shstrndx of your favourite hello world program.
> I suppose one way to provide something that gdb and other tools expect
> would be to treat the vdso like a core file, and create fake sections
> corresponding to the program headers. I'm not really keen on the idea
> though, since I know that will open up a can of worms.
I think a case can be made that gdb should be able to use the
"execution view" of the program here.
As for how to achieve that ... "Discuss." :-)