[LLVMdev] error: instruction requires: thumb2

[Lei Zhao]

Hi Everybody,

I recently did a cross-compiling using clang (built with host=x86, target=arm) with the following command:

> clang -march=armv7-a -mfloat-abi=soft -ccc-host-triple arm-none-linux-gnueabi -integrated-as main.c -o main.o -c

and get error message:

-------------------------------------------------------
main.c:9:9: error: instruction requires: thumb2
"ldrex %[oldValue], [%[ptr], #0]\n" // oldValue = *ptr
^
<inline asm>:1:2: note: instantiated into assembly here
ldrex r6, [r4, #0]
^
main.c:11:3: error: instruction requires: thumb2
"strexeq %[failed], %[newValue], [%[ptr], #0]\n"
^
<inline asm>:3:1: note: instantiated into assembly here
strexeq r5, lr, [r4, #0]
^
2 errors generated.
-------------------------------------------------------

In the main.c, some ARM assembly are embedded which contains instructions ldrex, strexeq. I don't know what the message suggests since the cpu specified does support thumb2. Could someone help? Thanks.

- Lei



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[Eli Friedman]

On Thu, Aug 16, 2012 at 12:55 PM, Lei Zhao <leizh...@gmail.com> wrote:
> Hi Everybody,
>
> I recently did a cross-compiling using clang (built with host=x86, target=arm) with the following command:
>
> > clang -march=armv7-a -mfloat-abi=soft -ccc-host-triple arm-none-linux-gnueabi -integrated-as main.c -o main.o -c
>
> and get error message:
>
> -------------------------------------------------------
> main.c:9:9: error: instruction requires: thumb2
> "ldrex %[oldValue], [%[ptr], #0]\n" // oldValue = *ptr
> ^
> <inline asm>:1:2: note: instantiated into assembly here
> ldrex r6, [r4, #0]
> ^
> main.c:11:3: error: instruction requires: thumb2
> "strexeq %[failed], %[newValue], [%[ptr], #0]\n"
> ^
> <inline asm>:3:1: note: instantiated into assembly here
> strexeq r5, lr, [r4, #0]
> ^
> 2 errors generated.
> -------------------------------------------------------
>
> In the main.c, some ARM assembly are embedded which contains instructions ldrex, strexeq. I don't know what the message suggests since the cpu specified does support thumb2. Could someone help? Thanks.

Try "-mthumb".

-Eli

[Lei Zhao]

It works. Thanks.

- Lei

[Lei Zhao]

It works. But a follow-up question: why do I have to compile it to thumb mode in order to pass the compilation? Is there a way to make it compile to regular arm mode? Thanks.

- Lei

On Aug 16, 2012, at 4:00 PM, Eli Friedman wrote:

[Jim Grosbach]

Sure. Use legal ARM mode syntax for the instruction.

Specifically, there is no offset immediate for the ARM mode LDREX instruction. It's illegal syntax to supply one, even if it's zero.

-Jim

[Lei Zhao]

Aha, thanks.

- Lei