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Message-ID: <CAH9TF6MA+81k1VMAa4W1pJ8Ax-4aPB-qWdiz0iwmOr=FZvWbfA@mail.gmail.com>
Date: Sat, 22 Feb 2025 02:32:45 +0100
From: Alex Rønne Petersen <alex@...xrp.com>
To: Rich Felker <dalias@...c.org>
Cc: musl@...ts.openwall.com
Subject: Re: [PATCH v2] clone: clear the frame pointer in the child
process on relevant ports
On Sat, Feb 22, 2025 at 2:06 AM Rich Felker <dalias@...c.org> wrote:
>
> On Thu, Dec 12, 2024 at 05:56:04PM +0100, Alex Rønne Petersen wrote:
> > This just mirrors what is done in the start code for the affected ports, as well
> > as what is already done for the three x86 ports.
> >
> > Clearing the frame pointer helps protect FP-based unwinders which have no way of
> > knowing that the FP register should be considered undefined in the child process
> > portion of clone(). In practice, we found this change to be necessary when
> > running the Zig standard library tests under qemu-aarch64_be with musl linked.
> >
> > This version of the patch omits the branch inversion on x86 and powerpc from the
> > previous version, per the discussion there.
>
> Trying to apply this, but...
>
> > diff --git a/src/thread/m68k/clone.s b/src/thread/m68k/clone.s
> > index f6dfa06f..42ec19f7 100644
> > --- a/src/thread/m68k/clone.s
> > +++ b/src/thread/m68k/clone.s
> > @@ -18,7 +18,8 @@ __clone:
> > beq 1f
> > movem.l (%sp)+,%d2-%d5
> > rts
> > -1: move.l %a1,-(%sp)
> > +1: suba.l %%fp,%%fp
> > + move.l %a1,-(%sp)
> > jsr (%a0)
> > move.l #1,%d0
> > trap #0
>
> This does not assemble and is most likely not valid. I get:
>
> src/thread/m68k/clone.s:21: Error: operands mismatch -- statement `suba.l %%fp,%%fp' ignored
>
> Do you know what the right instruction to use here is for m68k? And,
> have you tested that the rest of the affected archs build?
Sorry, this was a silly mistake from copying the code from inline
assembly in Zig, where % has to be escaped with an extra %. It should
just simply be suba.l %fp,%fp.
Beyond that, I've assembled all of the archs affected here
successfully, and for those that LLVM supports, they've been tested by
way of Zig's test suite under QEMU.
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