Re: [PATCH] cortex-m3: adjusted target cflags

[Mark Hatle <mark.hatle@windriver.com>]

On 2/7/11 2:19 PM, Khem Raj wrote:
> On Mon, Feb 7, 2011 at 11:39 AM, Mark Hatle <mark.hatle@windriver.com> wrote:
>> On 2/7/11 1:33 PM, Khem Raj wrote:
>>> On Mon, Feb 7, 2011 at 7:53 AM, Enrico Scholz
>>> <enrico.scholz@sigma-chemnitz.de> wrote:
>>>> Explicit '-mthumb' is required because Cortex-M3 does not support ARM
>>>> instructions and actual flags cause gcc to fail with 'error: target CPU
>>>> does not support ARM mode'.
>>>>
>>>> The '-mcpu=cortex-m3' is shorter than '-march=armv7-m -mtune=cortex-m3'
>>>> and enables workarounds like '-mfix-cortex-m3-ldrd'.
>>>
>>> Does -mcpu=cortex-m3 also cause gcc to tune for cortex-m3 ?
>>
>> -mcpu=cortex-m3 is equivalent to -march=cortex-m3 -mtune=cortex-m3
> 
> is -march=cortex-m3 valid even ? my question was if we select armv7-m
> using -march
> then gcc knows stuff like oh this arch has a hardware div instruction
> but now if we
> use -mcpu will it still do it.

You would have to look in the source and see if -mcpu=cortex-m3 is an "alias"
for anything or simply uses the default logic of cpu == march && mtune..

(FYI, last time I looked at how this worked was a year or so ago.. so if the way
GCC processes options has changed, then I'm wrong..  but it's worth looking at..
 I was scolded many times by GCC developers that -mcpu= is not the same as
specifically setting the arch and tune.)

Usually you use march & mtune when you are trying to make a set of binaries that
is capable of running on multiple cores in the same family.  I see it used the
most of IA and Power systems myself.

--Mark