Re: vDSO parsing bug?

[Rich Felker <dalias@aerifal.cx>]

On Thu, Mar 20, 2014 at 08:23:24AM -0700, Andy Lutomirski wrote:
> Hi-
> 
> It looks like musl can't handle vDSO images with more than one PT_LOAD
> segment.  Both glibc and the reference code in
> Documentation/vDSO/parse_vdso.c can handle this.

I'm not clear on what you think is wrong. The computation of
vdso->base? That's all musl uses the PT_LOAD header for.

> It's not currently an issue, since I don't think that any
> architectures provide such a vDSO, but they might want to in the
> future.
> 
> Also, using the name "linux-gate.so.1" is sort of wrong on x86_64,
> where the convention is "linux-vdso.so.1".  Wouldn't it be better to
> just read the name out of the SONAME header?

Yes, that sounds like a better solution. I just didn't realize it was
an option.

BTW the vdso usage is currently broken as far as I can tell. Due to
the way musl binds function references at link time, the weak-alias
setup that's intended to allow the vdso functions to interpose does
not actually work.

I'm thinking it might be better to avoid accessing the vdso through
the dynamic linker like this and simply parsing it directly in code
that can be used in static-linked programs too. Then it's not clear to
me whether the dynamic linker would even need to report the vdso in
the link map, but maybe it still should to assist gdb...?

I'd welcome further input on this topic.

Rich