llvm dev - Sep 2015 - Invalid instruction generated on armV4

I’m using rust head version that currently use llvm 3.7 … 

Thanks.

Frédéric.
> On 11 Sep 2015, at 13:29, Bruce Hoult <bruce at hoult.org> wrote:
> 
> What LLVM version are you using?
> 
> There were some bugs around switching ARM/Thumb mode on ARMv4 fixed in 3.6.
> 
> On Fri, Sep 11, 2015 at 1:20 PM, Frédéric Richez <llvm-dev at
lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> I’m tying to run a rust application on armv4 architecture (arm720tdmi).
> Rust is using llvm to generate native code.
> Some programs are running well on the target but for more complex
applications I receive a Illegal instruction :
> gdb disassembling the core dump file gives :
> 
>    0x401e41dc <+0>:	push	{r11, lr}
>    0x401e41e0 <+4>:	mov	r11, sp
>    0x401e41e4 <+8>:	sub	sp, sp, #8
>    0x401e41e8 <+12>:	ldr	r0, [r0]
>    0x401e41ec <+16>:	str	r0, [sp, #4]
>    0x401e41f0 <+20>:	mov	r0, r1
>    0x401e41f4 <+24>:	ldr	r1, [sp, #4]
> => 0x401e41f8 <+28>:	blx	r1
>    0x401e41fc <+32>:	and	r0, r0, #1
>    0x401e4200 <+36>:	and	r0, r0, #1
>    0x401e4204 <+40>:	mov	sp, r11
>    0x401e4208 <+44>:	pop	{r11, lr}
>    0x401e420c <+48>:	bx	lr
> blx instruction is available from ARM architecture v5 and above…
> 
> After lot of investigations I found where llvm is generating this
instruction :
>
https://github.com/rust-lang/llvm/blob/168f91ce5cbf8933e47f339911f0f46a48714852/lib/Target/ARM/ARMFastISel.cpp#L2395
<https://github.com/rust-lang/llvm/blob/168f91ce5cbf8933e47f339911f0f46a48714852/lib/Target/ARM/ARMFastISel.cpp#L2395>
> UseReg variable is true causing ARMSelectCallOp function to set a BLX
instruction that is not supported on armv4 :-(
> 
> Could you help me to solve this ? 
> 
> Many thanks
> 
> Frédéric.
> 
> 
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> 
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On 11 September 2015 at 12:41, Frédéric Richez <llvm-dev at
lists.llvm.org> wrote:
> I’m using rust head version that currently use llvm 3.7 …
Yes, I saw that, tracking the GitHub repo relatively closely.

I also thought about that v4 bug on the same area from 3.6, but this
seems to be a new one.

I think the best thing to do now is to create a bugzilla entry with as
much information as you can. If possible, try to reduce to a piece of
IR that reproduces the failure with standard tools. If not, the more
you can provide the better, so at least we can help you debug the
problem.

cheers,
--renato

On 9/11/15 5:43 AM, Renato Golin via llvm-dev wrote:
> On 11 September 2015 at 12:41, Frédéric Richez <llvm-dev at
lists.llvm.org> wrote:
>> I’m using rust head version that currently use llvm 3.7 …
>
> Yes, I saw that, tracking the GitHub repo relatively closely.
>
> I also thought about that v4 bug on the same area from 3.6, but this
> seems to be a new one.
>
> I think the best thing to do now is to create a bugzilla entry with as
> much information as you can. If possible, try to reduce to a piece of
> IR that reproduces the failure with standard tools. If not, the more
> you can provide the better, so at least we can help you debug the
> problem.
I wish I had set up a v4/v4t buildbot :(


Jon
>
> cheers,
> --renato
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
-- 
Jon Roelofs
jonathan at codesourcery.com
CodeSourcery / Mentor Embedded

Thanks renato I will try to do this but it is quite difficult for me, I don’t
known a lot about llvm project, not more than wikipedia definition ;-)
I had a look on ARMFatsISel source file history. In 2012 a change concerning
“support for non-global callee” has removed a guard condition in SelectCall
method.
<<https://github.com/llvm-mirror/llvm/commit/1c8fccbc12e6348c8003aff9b89078324257fc4e
<https://github.com/llvm-mirror/llvm/commit/1c8fccbc12e6348c8003aff9b89078324257fc4e>>>

 // Only handle global variable Callees.
const GlobalValue *GV = dyn_cast<GlobalValue>(Callee);
if (!GV)
    return false;

I restored this peace of code in my local llvm source code, rebuild rust and …
no more blx instruction generated, all my run programs seems to run correctly !
I’m sure it is not a solution but it could help to solve/understand the issue.

Have a nice we.

Frédéric.

> On 11 Sep 2015, at 13:43, Renato Golin <renato.golin at linaro.org>
wrote:
> 
> On 11 September 2015 at 12:41, Frédéric Richez <llvm-dev at
lists.llvm.org> wrote:
>> I’m using rust head version that currently use llvm 3.7 …
> 
> Yes, I saw that, tracking the GitHub repo relatively closely.
> 
> I also thought about that v4 bug on the same area from 3.6, but this
> seems to be a new one.
> 
> I think the best thing to do now is to create a bugzilla entry with as
> much information as you can. If possible, try to reduce to a piece of
> IR that reproduces the failure with standard tools. If not, the more
> you can provide the better, so at least we can help you debug the
> problem.
> 
> cheers,
> --renato
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