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Date: Wed, 28 Feb 2024 11:34:27 -0800
From: Max Filippov <jcmvbkbc@...il.com>
To: Rich Felker <dalias@...c.org>
Cc: musl@...ts.openwall.com
Subject: Re: Initial xtensa/fdpic port review
On Wed, Feb 28, 2024 at 10:36 AM Rich Felker <dalias@...c.org> wrote:
> On Wed, Feb 28, 2024 at 01:30:32PM -0500, Rich Felker wrote:
> > On Wed, Feb 28, 2024 at 09:20:33AM -0800, Max Filippov wrote:
> > >
> > > > > p->relocated = 1;
> > > > > }
> > > > > @@ -1485,7 +1487,7 @@ void __libc_exit_fini()
> > > > > if (dyn[0] & (1<<DT_FINI_ARRAY)) {
> > > > > size_t n = dyn[DT_FINI_ARRAYSZ]/sizeof(size_t);
> > > > > size_t *fn = (size_t *)laddr(p, dyn[DT_FINI_ARRAY])+n;
> > > > > - while (n--) ((void (*)(void))*--fn)();
> > > > > + while (n--) fpaddr(p, *--fn)();
> > > >
> > > > If this is fixable on the tooling side it really should be fixed
> > > > there. init/fini arrays should have actual language-level function
> > > > addresses (descriptor addresses on fdpic), not instruction addresses.
> > >
> > > I read libgcc code at
> > > https://github.com/jcmvbkbc/gcc-xtensa/blob/xtensa-14-8789-fdpic/libgcc/crtstuff.c#L498-L503
> > > and the way it's written suggests that this was done on purpose.
> > > I put it into the WIP pile to figure out later what the purpose was.
> > > I thought that SH might not have this issue because it just didn't
> > > use the .array_init/.array_fini.
> >
> > I'm pretty sure we're using it -- musl-cross-make always forces it on
> > via the gcc configure command line -- but it's possible there's some
> > override disabling it for sh. I'll try some test cases and confirm
> > whether sh is doing it right. Maybe the arm folks will have input on
> > this too..?
>
> Confirmed both that it works, and that it's working via init_array.
> GCC emits:
>
> .section .init_array,"aw"
> .align 2
> .long foo@...CDESC
>
> for
>
> __attribute__((__constructor__))
> void foo() { ... }
>
Oh, no doubt that that C code generates a function descriptor, it
works for xtensa too. But the piece of libgcc quoted above specifically
puts a pointer to an object, not to a function into the .init_array.
> Also, FWIW, I believe there's something of an application-facing
> contract that you can declare function pointer arrays with
> __attribute__((__section__(".init_array"))) and have them work, which
> would not work if instruction addresses rather than function addresses
> are expected to be there.
--
Thanks.
-- Max
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