Re: [PATCH] arm64: traps: Add a macro to simplify the condition codes check

[Marc Zyngier <maz@kernel.org>]

On Thu, 23 Apr 2026 06:29:09 +0100,
Anshuman Khandual <anshuman.khandual@arm.com> wrote:
> 
> 
> 
> On 20/03/26 1:58 PM, Jinjie Ruan wrote:
> > Add DEFINE_COND_CHECK macro to define the simple __check_* functions
> > to simplify the condition codes check.
> > 
> > No functional changes.
> > 
> > Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
> > ---
> >  arch/arm64/kernel/traps.c | 59 ++++++++++-----------------------------
> >  1 file changed, 15 insertions(+), 44 deletions(-)
> > 
> > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> > index 914282016069..6216fe9e8e42 100644
> > --- a/arch/arm64/kernel/traps.c
> > +++ b/arch/arm64/kernel/traps.c
> > @@ -49,45 +49,21 @@
> >  #include <asm/system_misc.h>
> >  #include <asm/sysreg.h>
> >  
> > -static bool __kprobes __check_eq(unsigned long pstate)
> > -{
> > -	return (pstate & PSR_Z_BIT) != 0;
> > -}
> > -
> > -static bool __kprobes __check_ne(unsigned long pstate)
> > -{
> > -	return (pstate & PSR_Z_BIT) == 0;
> > -}
> > -
> > -static bool __kprobes __check_cs(unsigned long pstate)
> > -{
> > -	return (pstate & PSR_C_BIT) != 0;
> > -}
> > -
> > -static bool __kprobes __check_cc(unsigned long pstate)
> > -{
> > -	return (pstate & PSR_C_BIT) == 0;
> > -}
> > -
> > -static bool __kprobes __check_mi(unsigned long pstate)
> > -{
> > -	return (pstate & PSR_N_BIT) != 0;
> > -}
> > -
> > -static bool __kprobes __check_pl(unsigned long pstate)
> > -{
> > -	return (pstate & PSR_N_BIT) == 0;
> > -}
> > -
> > -static bool __kprobes __check_vs(unsigned long pstate)
> > -{
> > -	return (pstate & PSR_V_BIT) != 0;
> > -}
> > -
> > -static bool __kprobes __check_vc(unsigned long pstate)
> > -{
> > -	return (pstate & PSR_V_BIT) == 0;
> > -}
> > +#define DEFINE_COND_CHECK(name, flag, expected)			\
> > +static bool __kprobes __check_##name(unsigned long pstate)	\
> > +{								\
> > +	return ((pstate & (flag)) != 0) == (expected);		\
> > +}
> > +
> > +DEFINE_COND_CHECK(eq, PSR_Z_BIT, true)
> > +DEFINE_COND_CHECK(ne, PSR_Z_BIT, false)
> > +DEFINE_COND_CHECK(cs, PSR_C_BIT, true)
> > +DEFINE_COND_CHECK(cc, PSR_C_BIT, false)
> > +DEFINE_COND_CHECK(mi, PSR_N_BIT, true)
> > +DEFINE_COND_CHECK(pl, PSR_N_BIT, false)
> > +DEFINE_COND_CHECK(vs, PSR_V_BIT, true)
> > +DEFINE_COND_CHECK(vc, PSR_V_BIT, false)
> > +DEFINE_COND_CHECK(al, 0, false)		/* Always true */
> 
> 	(((pstate & 0 == 0) != 0) == false) ---> return true 
> 
> Although this looks OK but wondering if __check_al() should
> be left unchanged for simplicity. OR could all its call sites
> be changed assuming an unconditional 'true' return thus later
> __check_al() can be dropped.

Which call site? We emulate an instruction, and we're not in control
of the condition code associated with it. The condition code directly
indexes into aarch32_opcode_cond_checks[].

Anyway, this is a moot point, as we have consensus to not touch that
code at all.

	M.

-- 
Without deviation from the norm, progress is not possible.