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ARM Vs GCC assembler

Note: This was originally posted on 25th January 2013 at http://forums.arm.com

Hi,

I have a question regarding the ARM and GCC assemblers i.e. ARMASM and GAS.

MOV.W R4,#0x87C0 is translated to F248_74C0 by ARMASM.

However, GAS throws up the error "invalid constant (87c0) after fixup" for the same instruction. Why does GAS give an error for this?

I realise the operand is 16-bit but I'm using the '.syntax unified'. I thought GAS supports .W and .N suffixes. Even without the .W suffix, GAS gives the same error whereas ARMASM quietly expands the 16-bit instruction to 32-bit.

I'm using 'GCC version 4.7.2 (Sourcety CodeBench Lite 2012.09-63).

Any insight as to why GAS is giving an error is appreciated. The workaround is to use two instructions. The following 2 instructions compile OK.

MOVW R4 ,#0xC0
MOVT R4 ,#0x87

Thanks and regards,
Ger

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Kenneth Hass over 12 years ago

Note: This was originally posted on 25th January 2013 at http://forums.arm.com

For ARMv7-M,
MOV.W R4, #87C0
is incorrect but
MOVW R4, #87C0
is assembled by the gnu assembler to f248 74c0, using the T3 encoding of the MOV instruction.
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Kenneth Hass over 12 years ago

Note: This was originally posted on 25th January 2013 at http://forums.arm.com

For ARMv7-M,
MOV.W R4, #87C0
is incorrect but
MOVW R4, #87C0
is assembled by the gnu assembler to f248 74c0, using the T3 encoding of the MOV instruction.
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