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Date: Tue, 5 Jan 2016 12:32:00 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: dynamic linker command line invocation
On Tue, Jan 05, 2016 at 11:45:01AM -0500, N Jain wrote:
> Hi Rich,
>
> Thanks. Right now I am following second approach due to simplicity.
> I understand about race condition so does it mean that currently the MUSL
> dynamic linker will not gracefully handle such situation where the
> executable is moved/replaced ?
No, it's not something you can "handle" but an inherent race
condition. To avoid it the kernel would have to refrain from passing
the actual pathname to the file but instead some virtual pathname like
/proc/self/main_exe (hypothetical) that would be tied to the original
inode the user tried to execute.
> During further debug I found that passed parameters to dynamic linker are
> correct and argv[0] does have dynamically "app.elf".
> Also I am loading the dynamic linker at fixed load offset 0x8000 so I
> needed to adjust my all dynamic linker LOAD sections accordingly which was
> causing issues previously.
Hm? You should not be making any adjustments. The dynamic linker
applies its own relocations to itself when run. You just need to pass
it the right pointers in the aux vector. You never answered whether
you were setting up the aux vector right, but if not, that's
definitely going to cause problems.
> Now I am facing issue during __dls3 API (stage 3). I would like to know if
> I can enable "dprintfs" in MUSL code in order to easily debug ?
> What I have to do in order to enable these "dprintfs" ?
dprintf is a standard function for printing to a file descriptor, not
a debug function. It's definitely usable by the time you reach stage 3
and should also be usable during stage 2. On x86 linked with
-Bsymbolic-functions (as we do now) it may even work at stage 1.
Rich
P.S. Please don't top-post to the list but instead reply inline/below
the text you're replying to, and edit to include only relevant
context.
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