Re: [PATCH] spmi: pmic-arb: bound id before using it as the IRQ ID field in spec_to_hwirq()

[Abel Vesa]

On 26-11-03 15:35:16, Jishnu Prakash wrote:
> periph_interrupt() derives id from ffs(status) - 1, giving the compiler
> no source-level guarantee that id stays within the 3-bit range of
> HWIRQ_IRQID_MASK before it is passed to spec_to_hwirq()'s
> FIELD_PREP(HWIRQ_IRQID_MASK, id). On targets where ffs() has no native
> instruction and is expanded in software (e.g. MIPS), the expansion's
> internal handling of the "no bit set" case lets some compilers prove id
> is a literal that overflows the field along that path, even though the
> enclosing while (status) loop guarantees it is never taken. This trips
> FIELD_PREP()'s compile-time "value too large for the field" check.
> 
> Clamp id to HWIRQ_IRQID_MASK's width (via FIELD_MAX()) right after
> computing it, so the "no bit set" literal is bounded to the field's max
> value instead of overflowing it.
> 
> Root cause and fix were diagnosed and verified with AI assistance.
> Reviewed and tested by the author.
> 
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-kbuild-all/202610260532.Zb5KDgRE-lkp@xxxxxxxxx/
> Fixes: 815be38ad8c8 ("spmi: spmi-pmic-arb: add support for PMIC arbiter v8")
> Signed-off-by: Jishnu Prakash <jishnu.prakash@xxxxxxxxxxxxxxxx>

Reviewed-by: Abel Vesa <abel.vesa@xxxxxxxxxxxxxxxx>