Le 04/08/2020 à 13:17, Christophe Leroy a écrit :
On 07/16/2020 02:59 AM, Michael Ellerman wrote:
Christophe Leroy <christophe.leroy@xxxxxx> writes:
The VDSO datapage and the text pages are always located immediately
next to each other, so it can be hardcoded without an indirection
through __kernel_datapage_offset
In order to ease things, move the data page in front like other
arches, that way there is no need to know the size of the library
to locate the data page.
[...]
I merged this but then realised it breaks the display of the vdso in
/proc/self/maps.
ie. the vdso vma gets no name:
# cat /proc/self/maps
[...]
And it's also going to break the logic in arch_unmap() to detect if
we're unmapping (part of) the VDSO. And it will break arch_remap() too.
And the logic to recognise the signal trampoline in
arch/powerpc/perf/callchain_*.c as well.
I don't think it breaks that one, because ->vdsobase is still the start
of text.
So I'm going to rebase and drop this for now.
Basically we have a bunch of places that assume that vdso_base is == the
start of the VDSO vma, and also that the code starts there. So that will
need some work to tease out all those assumptions and make them work
with this change.
Ok, one day I need to look at it in more details and see how other
architectures handle it etc ...
I just sent out a series which switches powerpc to the new
_install_special_mapping() API, the one powerpc uses being deprecated
since commit a62c34bd2a8a ("x86, mm: Improve _install_special_mapping
and fix x86 vdso naming")
arch_remap() gets replaced by vdso_remap()
For arch_unmap(), I'm wondering how/what other architectures do, because
powerpc seems to be the only one to erase the vdso context pointer when
unmapping the vdso. So far I updated it to take into account the pages
switch.
Everything else is not impacted because our vdso_base is still the base
of the text and that's what those things (signal trampoline, callchain,
...) expect.
Maybe we should change it to 'void *vdso' in the same way as other
architectures, as it is not anymore the exact vdso_base but the start of
VDSO text.
Note that the series applies on top of the generic C VDSO implementation
series. However all but the last commit cleanly apply without that
series. As that last commit is just an afterwork cleanup, it can come in
a second step.
Christophe
