llvm dev - Jun 2013 - [LLVMdev] Apple clang 4.2 based on llvm 3.2 produces a wrong "instruction requires:arm-mode"

Hi,
I've got an assembly file which used to compile with previous clang
versions. However with 4.2 I get the following error:
admin$
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang
-arch armv7 ./src/asm.s  -o asm.o

./src/asm.s:30:5: error: instruction requires
a CPU feature not currently enabled

    add r2, pc, r2
According to ARM specification:Use of PC and SP in Thumb instructionsIn most of
these instructions, you cannot use PC (R15) for Rd, or any operand.The
exceptions are:you can use PC for Rn in 32-bit Thumb ADD and SUB instructions,
with a constant Operand2 value in the range 0-4095, and no S suffix. These
instructions are useful for generating PC-relative addresses. Bit[1] of the PC
value reads as 0 in this case, so that the base address for the calculation is
always word-aligned.you can use PC in 16-bit Thumb ADD{cond} Rd, Rd, Rm
instructions, where both registers cannot be PC.

I indeed specified that this line belongs to the Thumb function. But the clang
still produces this error.
When I compile this file directly with "as" it compiles correctly.

Please help!
  		 	   		  
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Moshe,

You're more than likely going to get a better response from

https://devforums.apple.com/community/tools/xcode

llvmdev is a mailing list for the LLVM project which is separate from Xcode
development.

Cheers,

Joe

On Jun 12, 2013, at 8:51 AM, Moshe Kravchik <mkravchik at
hotmail.com<mailto:mkravchik at hotmail.com>> wrote:

Hi,

I've got an assembly file which used to compile with previous clang
versions. However with 4.2 I get the following error:

admin$
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang
-arch armv7 ./src/asm.s  -o asm.o
./src/asm.s:30:5: error: instruction requires a CPU feature not currently
enabled
    add r2, pc, r2

According to ARM
<http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0489c/Cihcjfjg.html>
specification:
[http://infocenter.arm.com/help/topic/com.arm.doc.common/images/triangle_down.png]Use
of PC and SP in Thumb instructions
In most of these instructions, you cannot use PC (R15) for Rd, or any operand.
The exceptions are:

 *
you can use PC for Rn in 32-bit Thumb ADD and SUB instructions, with a constant
Operand2 value in the range 0-4095, and no S suffix. These instructions are
useful for generating PC-relative addresses. Bit[1] of the PC value reads as 0
in this case, so that the base address for the calculation is always
word-aligned.
 *
you can use PC in 16-bit Thumb ADD{cond} Rd, Rd, Rm instructions, where both
registers cannot be PC.


I indeed specified that this line belongs to the Thumb function. But the clang
still produces this error.

When I compile this file directly with "as" it compiles correctly.


Please help!




_______________________________________________
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LLVMdev at cs.uiuc.edu<mailto:LLVMdev at cs.uiuc.edu>        
http://llvm.cs.uiuc.edu
http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

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There is also this forum:

https://devforums.apple.com/community/tools/llvm

Cheers,

Joe

On Jun 12, 2013, at 9:02 AM, Joe Abbey <jabbey at arxan.com<mailto:jabbey
at arxan.com>> wrote:

Moshe,

You're more than likely going to get a better response from

https://devforums.apple.com/community/tools/xcode

llvmdev is a mailing list for the LLVM project which is separate from Xcode
development.

Cheers,

Joe

On Jun 12, 2013, at 8:51 AM, Moshe Kravchik <mkravchik at
hotmail.com<mailto:mkravchik at hotmail.com>> wrote:

Hi,

I've got an assembly file which used to compile with previous clang
versions. However with 4.2 I get the following error:

admin$
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang
-arch armv7 ./src/asm.s  -o asm.o
./src/asm.s:30:5: error: instruction requires a CPU feature not currently
enabled
    add r2, pc, r2

According to ARM
<http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0489c/Cihcjfjg.html>
specification:
[http://infocenter.arm.com/help/topic/com.arm.doc.common/images/triangle_down.png]Use
of PC and SP in Thumb instructions
In most of these instructions, you cannot use PC (R15) for Rd, or any operand.
The exceptions are:

 *
you can use PC for Rn in 32-bit Thumb ADD and SUB instructions, with a constant
Operand2 value in the range 0-4095, and no S suffix. These instructions are
useful for generating PC-relative addresses. Bit[1] of the PC value reads as 0
in this case, so that the base address for the calculation is always
word-aligned.
 *
you can use PC in 16-bit Thumb ADD{cond} Rd, Rd, Rm instructions, where both
registers cannot be PC.


I indeed specified that this line belongs to the Thumb function. But the clang
still produces this error.

When I compile this file directly with "as" it compiles correctly.


Please help!




_______________________________________________
LLVM Developers mailing list
LLVMdev at cs.uiuc.edu<mailto:LLVMdev at cs.uiuc.edu>        
http://llvm.cs.uiuc.edu<http://llvm.cs.uiuc.edu/>
http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev


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Hi Moshe,

The others are right that you'll likely get better Apple-specific help
at the forums, but this problem happens to be the same in generic
LLVM.
> ./src/asm.s:30:5: error: instruction requires a CPU feature not currently
enabled
>
>     add r2, pc, r2
>
> According to ARM specification:
The specifications you're referring to are a little vague, and the
actual instruction definitions give the real situation (page/section
A3-308).

I think it boils down to:
"add r2, r2, pc" should be allowed (but LLVM doesn't, this is a
bug).
"add r2, pc" should be allowed (and is)
"add r2, pc, r2" should be allowed *if* it's in an IT block (but
LLVM
doesn't, this is a bug).

That last one might be rather tricky to implement. I'll take a bit of
a look, but may not have time to do it properly. Reporting it at
llvm.org/bugs (and/or bugreporter.apple.com since that seems to be
your platform) would make sure it doesn't get lost.

Cheers.

Tim.

So probably it is a LLVM issue - can anyone from the team look at it and let me
know if there is anything to do.
Moshe
> Date: Wed, 12 Jun 2013 10:53:56 -0700
> Subject: Re: [LLVMdev] Apple clang 4.2 based on llvm 3.2 produces a wrong
"instruction requires:arm-mode"
> From: t.p.northover at gmail.com
> To: mkravchik at hotmail.com
> CC: llvmdev at cs.uiuc.edu
> 
> Hi Moshe,
> 
> The others are right that you'll likely get better Apple-specific help
> at the forums, but this problem happens to be the same in generic
> LLVM.
> 
> > ./src/asm.s:30:5: error: instruction requires a CPU feature not
currently enabled
> >
> >     add r2, pc, r2
> >
> > According to ARM specification:
> 
> The specifications you're referring to are a little vague, and the
> actual instruction definitions give the real situation (page/section
> A3-308).
> 
> I think it boils down to:
> "add r2, r2, pc" should be allowed (but LLVM doesn't, this is
a bug).
> "add r2, pc" should be allowed (and is)
> "add r2, pc, r2" should be allowed *if* it's in an IT block
(but LLVM
> doesn't, this is a bug).
> 
> That last one might be rather tricky to implement. I'll take a bit of
> a look, but may not have time to do it properly. Reporting it at
> llvm.org/bugs (and/or bugreporter.apple.com since that seems to be
> your platform) would make sure it doesn't get lost.
> 
> Cheers.
> 
> Tim.
 		 	   		  
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