[PATCH v3] ARM: document arm_setup_stack() pitfalls

[Sascha Hauer]

On Fri, Sep 17, 2021 at 02:11:52PM +0200, Ahmad Fatoum wrote:
> Many arm32 board entry points use arm_setup_stack() to set up
> the stack from C code. This necessitates using __naked, which
> probably has been our most frequent cause of misscompiled C code.
> 
> GCC is quite clear that:
> 
>   Only basic asm statements can safely be included in naked functions
>   While using extended asm or a mixture of basic asm and C code may
>   appear to work, they cannot be depended upon to work reliably and
>   are not supported.
> 
> But some boards use it anyway, because it's nice to avoid writing
> assembly. Reading generated assembly to spot compiler miscompilation
> isn't that nice though, so add some documentation, comments
> and compiler diagnostics to hopefully reduce future porting effort.
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
> ---
> v2 -> v3:
>   - fix typos (Uwe)
>   - use better matching CONFIG_CPU_64 instead of CONFIG_CPU_V8
>   - clarify 'bad' stack manipulation
> v1 -> v2:
>   - fix commit message title

Applied, thanks

Sascha


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