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Re: vdso handling
- From: Samuel Bronson <naesten at gmail dot com>
- To: gdb at sourceware dot org
- Cc: binutils at sourceware dot org
- Date: Sun, 01 Jun 2014 16:31:55 -0400
- 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> <CADPb22SAmK5JB3muW_nCvuHN5L-aOcdyzYNR+OtnM3bA1x_OJg at mail dot gmail dot com> <CAHACq4o=HmdCo1FPFL-96raf2UN805jvM=VZM-9dbKrmzJFJTw at mail dot gmail dot com> <20140313010147 dot GZ26922 at bubble dot grove dot modra dot org> <A78C989F6D9628469189715575E55B230AA9CDCB at IRSMSX103 dot ger dot corp dot intel dot com> <5321834E dot 9000509 at redhat dot com> <53218C92 dot 9050303 at redhat dot com>
Pedro Alves <palves@redhat.com> writes:
> On 03/13/2014 10:07 AM, Pedro Alves wrote:
>> Why's that? Why doesn't the memory-backed bfd paths take the same paths as
>> a file-backed bfd internally in bfd? It sounds to me that this should be
>> doable without duplication.
>
> BTW, I meant that for vDSO's only. The vsyscall page is not an elf,
> and therefore bfd still needs to be passed a template elf. For the
> latter, GDB would indeed need to work with the segments. Do we still
> care for vsyscall kernels? But for the former, bfd should just be
> able to read the whole DSO as a plain elf.
>
> Some glibc versions even include the vdso in the DSO list (*), and GDB
> should be able to tell that that DSO is the vDSO (by matching addresses), and
^^^^^^^^^^^^^^^^^^^^^
Hmm, why don't we already do that? It's bound to be easier than meeting
the conditions to get glibc to stop falsely cliaming that the vDSO comes
from a file <https://sourceware.org/bugzilla/show_bug.cgi?id=13097#c5>.
That'd be enough to take two bugs off of <http://bugs.debian.org/gdb>
right there.
> load it completely from memory, still using a memory backed bfd, but _without_
> a template. So with that in mind, bfd should be able to read the vdso
> as a bfd from memory using the same paths as a file-backed bfd, except,
> well, the bfd's backing store is in memory rather than in a file.
>
> (*) note how linux-vdso.so.1 is listed by ldd, even if "info shared" in gdb
> doesn't show it, on some systems.
What versions don't list the vdso under some name or other? (Mine calls
it linux-gate.so.1 for some reason.)
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