From: Will Springer <skirmisher@protonmail.com>
To: Rich Felker <dalias@libc.org>, linuxppc-dev@lists.ozlabs.org
Cc: binutils@sourceware.org, libc-dev@lists.llvm.org,
libc-alpha@sourceware.org, musl@lists.openwall.com,
daniel@octaforge.org, eery@paperfox.es
Subject: Re: [musl] ppc64le and 32-bit LE userland compatibility
Date: Sat, 30 May 2020 22:56:47 +0000 [thread overview]
Message-ID: <14083731.JCcGWNJJiE@sheen> (raw)
In-Reply-To: <20200529192426.GM1079@brightrain.aerifal.cx>
On Friday, May 29, 2020 12:24:27 PM PDT Rich Felker wrote:
> The argument passing for pread/pwrite is historically a mess and
> differs between archs. musl has a dedicated macro that archs can
> define to override it. But it looks like it should match regardless of
> BE vs LE, and musl already defines it for powerpc with the default
> definition, adding a zero arg to start on an even arg-slot index,
> which is an odd register (since ppc32 args start with an odd one, r3).
>
> > [6]:
> > https://gist.github.com/Skirmisher/02891c1a8cafa0ff18b2460933ef4f3c
> I don't think this is correct, but I'm confused about where it's
> getting messed up because it looks like it should already be right.
Hmm, interesting. Will have to go back to it I guess...
> > This was enough to fix up the `file` bug. I'm no seasoned kernel
> > hacker, though, and there is still concern over the right way to
> > approach this, whether it should live in the kernel or libc, etc.
> > Frankly, I don't know the ABI structure enough to understand why the
> > register padding has to be different in this case, or what
> > lower-level component is responsible for it.. For comparison, I had a
> > look at the mips tree, since it's bi-endian and has a similar 32/64
> > situation. There is a macro conditional upon endianness that is
> > responsible for munging long longs; it uses __MIPSEB__ and __MIPSEL__
> > instead of an if/else on the generic __LITTLE_ENDIAN__. Not sure what
> > to make of that. (It also simply swaps registers for LE, unlike what
> > I did for ppc.)
> Indeed the problem is probably that you need to swap registers for LE,
> not remove the padding slot. Did you check what happens if you pass a
> value larger than 32 bits?
>
> If so, the right way to fix this on the kernel side would be to
> construct the value as a union rather than by bitwise ops so it's
> endian-agnostic:
>
> (union { u32 parts[2]; u64 val; }){{ arg1, arg2 }}.val
>
> But the kernel folks might prefer endian ifdefs for some odd reason...
You are right, this does seem odd considering what the other archs do.
It's quite possible I made a silly mistake, of course...
I haven't tested with values outside the 32-bit range yet; again, this is
new territory for me, so I haven't exactly done exhaustive tests on
everything. I'll give it a closer look.
> > Also worth noting is the one other outstanding bug, where the
> > time-related syscalls in the 32-bit vDSO seem to return garbage. It
> > doesn't look like an endian bug to me, and it doesn't affect standard
> > syscalls (which is why if you run `date` on musl it prints the
> > correct time, unlike on glibc). The vDSO time functions are
> > implemented in ppc asm (arch/powerpc/kernel/vdso32/ gettimeofday.S),
> > and I've never touched the stuff, so if anyone has a clue I'm all
> > ears.
> Not sure about this. Worst-case, just leave it disabled until someone
> finds a fix.
Apparently these asm implementations are being replaced by the generic C
ones [1], so it may be this fixes itself on its own.
Thanks,
Will [she/her]
[1]: https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=173231
next prev parent reply other threads:[~2020-05-31 1:55 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-29 19:03 Will Springer
2020-05-29 19:24 ` Rich Felker
2020-05-30 22:56 ` Will Springer [this message]
2020-05-30 15:37 ` [musl] " Christophe Leroy
2020-05-30 22:17 ` Will Springer
2020-06-05 23:54 ` Will Springer
2020-06-12 5:13 ` Christophe Leroy
2020-05-30 19:22 ` Segher Boessenkool
2020-05-31 0:57 ` Will Springer
2020-05-31 20:42 ` Segher Boessenkool
2020-05-31 22:29 ` Daniel Kolesa
2020-06-02 1:36 ` Segher Boessenkool
2020-06-01 21:28 ` Joseph Myers
2020-06-01 21:36 ` Rich Felker
2020-06-01 23:26 ` Daniel Kolesa
2020-06-01 23:45 ` Joseph Myers
2020-06-01 23:55 ` Joseph Myers
2020-06-02 0:13 ` Daniel Kolesa
2020-06-02 0:11 ` Daniel Kolesa
2020-06-02 13:40 ` Joseph Myers
2020-06-02 14:23 ` Michal Suchánek
2020-06-02 15:13 ` Daniel Kolesa
2020-06-02 15:27 ` Michal Suchánek
2020-06-02 15:40 ` Daniel Kolesa
2020-06-02 15:56 ` Michal Suchánek
2020-06-04 17:20 ` Segher Boessenkool
2020-06-04 17:12 ` Segher Boessenkool
2020-06-04 17:18 ` Rich Felker
2020-06-04 17:33 ` Segher Boessenkool
2020-06-04 17:46 ` Rich Felker
2020-06-04 19:00 ` David Edelsohn
2020-06-04 19:37 ` Rich Felker
2020-06-04 20:39 ` Daniel Kolesa
2020-06-04 21:10 ` Segher Boessenkool
2020-06-04 21:43 ` Daniel Kolesa
2020-06-04 22:08 ` Joseph Myers
2020-06-04 22:26 ` Daniel Kolesa
2020-06-05 0:02 ` Segher Boessenkool
2020-06-04 23:42 ` Segher Boessenkool
2020-06-04 23:35 ` Segher Boessenkool
2020-06-05 2:18 ` Daniel Kolesa
2020-06-05 17:27 ` Segher Boessenkool
2020-06-05 17:50 ` Rich Felker
2020-06-05 23:45 ` Segher Boessenkool
2020-06-05 21:59 ` Daniel Kolesa
2020-06-06 0:12 ` Segher Boessenkool
2020-06-06 2:13 ` Daniel Kolesa
2020-06-02 14:52 ` Daniel Kolesa
2020-06-02 2:12 ` Segher Boessenkool
2020-06-02 2:17 ` Daniel Kolesa
2020-06-02 13:50 ` Joseph Myers
2020-06-02 17:47 ` Segher Boessenkool
2020-06-02 1:58 ` Segher Boessenkool
2020-06-02 2:09 ` Jeffrey Walton
2020-06-02 2:12 ` Daniel Kolesa
2020-06-02 2:36 ` Segher Boessenkool
2020-06-02 2:55 ` Daniel Kolesa
2020-06-02 1:42 ` Segher Boessenkool
2020-06-02 2:03 ` Daniel Kolesa
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=14083731.JCcGWNJJiE@sheen \
--to=skirmisher@protonmail.com \
--cc=binutils@sourceware.org \
--cc=dalias@libc.org \
--cc=daniel@octaforge.org \
--cc=eery@paperfox.es \
--cc=libc-alpha@sourceware.org \
--cc=libc-dev@lists.llvm.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=musl@lists.openwall.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/musl/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).