arm instruction width specifiers cannot be compiled

Question

I'm trying to disassemble and modify some code for arm. Disassembly shows some instructions with Instruction width specifiers, e.g:

 80002be:   f44f 5360   mov.w   r3, #14336  ; 0x3800
 80002c2:   f2c4 0302   movt    r3, #16386  ; 0x4002
 80002c6:   f44f 5260   mov.w   r2, #14336  ; 0x3800
 80002ca:   f2c4 0202   movt    r2, #16386  ; 0x4002

but when I'm trying to modify code and assemble, assembler doesn't like mov.w:

main.asm:5: Error: unexpected character `w' in type specifier
main.asm:5: Error: bad instruction `mov.w r3,#14336'

I tried specifying -mcpu=cortex-m4 -march=armv7-m -mthumb but it won't help. Any ideas?

with gcc? I only know a bit about ARM, but maybe this is something that only works that way in "unified" syntax mode (vs. the separate thumb-only syntax) — Peter Cordes

Notlikethat Notlikethat · Accepted Answer · 2016-11-29T09:33:28

Instruction width specifiers are part of the UAL syntax. It appears you're using the GNU assembler, which defaults to (a rather relaxed interpretation of) the legacy separate ARM/Thumb syntaxes, depending on -marm/-mthumb or the equivalent directives. If you want to properly use UAL features, you need to first set it with the .syntax unified directive.

arm instruction width specifiers cannot be compiled

1 Answers