[rust-dev] morestack prologue contains broken machine code

Vladimir Pouzanov farcaller at gmail.com
Mon Apr 21 10:34:05 PDT 2014


Hm, it seems to have precautions to stop mrc from materializing on Thumb1.
I guess I need to take a better look into what's going wrong on my side.
I'll see what I can do with that.


On Mon, Apr 21, 2014 at 5:23 PM, Alex Crichton <alex at crichton.co> wrote:

> The split stack patches for ARM were recently upstreamed, and they
> were modified when being upstreamed as well. Primarily the location of
> the split stack is no longer at a magic address for thumb, but rather
> it uses the same instruction as ARM (some thumb processors do indeed
> have the coprocessor). More information is in the long thread starting
> at the initial attempt to upstream [1].
>
> For now you'll have to use no_split_stack because the thumb split
> stack will always use a coprocessor, but I'm sure that the upstream
> LLVM devs would be quite welcoming to tweaks to the slit-stack support
> (I'd also be willing to help). You can find the initial commit for
> support at rust-lang/llvm [2].
>
> [1] -
> http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20140224/205968.html
> [2] - https://github.com/rust-lang/llvm/pull/4
>
> On Mon, Apr 21, 2014 at 6:50 AM, Vladimir Pouzanov <farcaller at gmail.com>
> wrote:
> > Starting recently (no more than two weeks), rustc is generating a broken
> > prologue for arm. Here's the sample assembly:
> >    0x00000f44 <+0>: push {r4, r5}
> > => 0x00000f46 <+2>: mrc 15, 0, r4, cr13, cr0, {3}
> >    0x00000f4a <+6>: mov r5, sp
> >    0x00000f4c <+8>: b.n 0xa78 <main+2616>
> >    0x00000f4e <+10>: ands r4, r0
> >    0x00000f50 <+12>: cmp r4, r5
> >    0x00000f52 <+14>: bcc.n 0xf66
> >
> <_ZN7drivers3lcd6c1233244C12332$LT$$x27a$C$$x20S$C$$x20T$GT$.lcd..LCD5flush20h76589116290686712394v0.0E+34>
> >    0x00000f54 <+16>: movs r4, #16
> >    0x00000f56 <+18>: movs r5, #0
> >    0x00000f58 <+20>: push {lr}
> >    0x00000f5a <+22>: bl 0x19d8 <__morestack>
> >    0x00000f5e <+26>: ldr.w lr, [sp], #4
> >    0x00000f62 <+30>: pop {r4, r5}
> >    0x00000f64 <+32>: bx lr
> >
> > The problem is at 0x00000f46, where code tries to read from coprocessor
> 15
> > register 13, which is "process id register". Well, coprocessor 15
> (actually,
> > all of the coprocessors) are missing from my target thumbv7m-linux-eabi
> > (with added flavour of -Ctarget-cpu=cortex-m3, which should be redundant
> > anyway), so I'm getting hardfaults in every function that rust doesn't
> > inline.
> >
> > Any ideas on what might be going wrong? I assume that this is actually
> > llvm's fault, as llvm should not materialize machine code which is not
> > available for target anyway.
> >
> > Wrapping everything in #[no_split_stack] is a temporary workaround and
> > surely not a long-term strategy.
> >
> > --
> > Sincerely,
> > Vladimir "Farcaller" Pouzanov
> > http://farcaller.net/
> >
> > _______________________________________________
> > Rust-dev mailing list
> > Rust-dev at mozilla.org
> > https://mail.mozilla.org/listinfo/rust-dev
> >
>



-- 
Sincerely,
Vladimir "Farcaller" Pouzanov
http://farcaller.net/
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