Re: [ptxdist] Toolchain for STM32MP15x

[Michael Olbrich <m.olbrich@pengutronix.de>]

On Mon, Nov 25, 2019 at 05:43:01PM +0100, Guillermo Rodriguez Garcia wrote:
> Hi all,
> 
> I have setup the toolchain with the settings from my previous email
> (-mcpu=cortex-a7 -mfpu=neon-vfpv4)
> 
> When I try to build the Linux kernel I get lots of warnings about
> conflicting toolchain options:
> 
> arch/arm/kernel/elf.c:1:0: warning: switch -mcpu=cortex-a7 conflicts
> with -march=armv5t switch

The problem is, that the kernel tries to add it's own -march=armv7-a and I
guess that causes warnings in combination with -mcpu=cortex-a7 (at least
with some gcc versions). This is tested with -Werror, so it fails. The
fallback is -march=armv5t ... (see arch/arm/Makefile in the kernel).

You cannot use -mcpu= in the extra cflags like this.

> This is with OSELAS.Toolchain-2016.06.1, using arm-v7a-linux-gnueabihf.
> 
> I am not sure where the -march=armv5t is coming from, since this is an
> arm-v7a toolchain.
> 
> Also if I use -mcpu=cortex-a9 instead of cortex-a7, there are no warnings :-?

This will have the same problem with gcc 9.x.

> Can anyone sehd some light ?

See above. Combining -march= with -mcpu= is not really supported and the
result is undefined. I'd say, just use -mfpu=neon-vfpv4. Have you tested if
-mcpu=cortex-a7 actually makes a difference?
I've done some tests with some other -mcpu= values and I've not seen any
real difference.

Michael

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