[fpc-devel] arm embedded cortexm3 procedure address

Geoffrey Barton mrb at periphon.net
Thu Jul 15 11:12:07 CEST 2010

On 14 Jul 2010, at 17:35, Jonas Maebe wrote:

> Geoffrey Barton wrote on Wed, 14 Jul 2010:
>> the resulting constant disassembles as:-
>> 1bc:	000001a5 	.word	0x000001a5
>> which seems to be one greater than the address of the procedure.
>> Is this right?
> Yes.
>> If so, why?
> To identify the code as Thumb code.

I was aware of the requirement to add one to the address of an ISR,  
but not to other calls.
A normal procedural call seems to assemble as a 'BL' to an even  
address? I must be missing something:-)

>> also, why does the compiler sometimes add a 'nop' to the end of a  
>> procedure (as above)?
> The default alignment of routines is 4 bytes. And it's most likely  
> the assembler or linker that adds the nop, rather than the compiler.

Yes, right. Probably the linker. Presumably because it is slightly  


> Jonas
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