linux-kernel - [PATCH 2/2] arm64: alternative: constify alternative_has_feature

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Message-Id: <20221006075542.2658-3-jszhang@kernel.org>
Date:   Thu,  6 Oct 2022 15:55:42 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Jason Baron <jbaron@...mai.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] arm64: alternative: constify alternative_has_feature_* argument

Inspired by x86 commit 864b435514b2("x86/jump_label: Mark arguments as
const to satisfy asm constraints"), constify alternative_has_feature_*
argument to satisfy asm constraints. And Steven in [1] also pointed
out that "The "i" constraint needs to be a constant."

Tested with building a simple external kernel module with "O0".

Before the patch, got similar gcc warnings and errors as below:

In file included from <command-line>:
In function ‘alternative_has_feature_likely’,
    inlined from ‘system_capabilities_finalized’ at
arch/arm64/include/asm/cpufeature.h:440:9,
    inlined from ‘arm64_preempt_schedule_irq’ at
arch/arm64/kernel/entry-common.c:264:6:
include/linux/compiler_types.h:285:33: warning:
‘asm’ operand 0 probably does not match constraints
  285 | #define asm_volatile_goto(x...) asm goto(x)
      |                                 ^~~
arch/arm64/include/asm/alternative-macros.h:232:9:
note: in expansion of macro ‘asm_volatile_goto’
  232 |         asm_volatile_goto(
      |         ^~~~~~~~~~~~~~~~~
include/linux/compiler_types.h:285:33: error:
impossible constraint in ‘asm’
  285 | #define asm_volatile_goto(x...) asm goto(x)
      |                                 ^~~
arch/arm64/include/asm/alternative-macros.h:232:9:
note: in expansion of macro ‘asm_volatile_goto’
  232 |         asm_volatile_goto(
      |         ^~~~~~~~~~~~~~~~~

After the patch, the simple external test kernel module is built fine
with "-O0".

[1]https://lore.kernel.org/all/20210212094059.5f8d05e8@gandalf.local.home/

Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
---
 arch/arm64/include/asm/alternative-macros.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/alternative-macros.h b/arch/arm64/include/asm/alternative-macros.h
index 3622e9f4fb44..bdf1f6bcd010 100644
--- a/arch/arm64/include/asm/alternative-macros.h
+++ b/arch/arm64/include/asm/alternative-macros.h
@@ -224,7 +224,7 @@ alternative_endif
 #include <linux/types.h>
 
 static __always_inline bool
-alternative_has_feature_likely(unsigned long feature)
+alternative_has_feature_likely(const unsigned long feature)
 {
 	compiletime_assert(feature < ARM64_NCAPS,
 			   "feature must be < ARM64_NCAPS");
@@ -242,7 +242,7 @@ alternative_has_feature_likely(unsigned long feature)
 }
 
 static __always_inline bool
-alternative_has_feature_unlikely(unsigned long feature)
+alternative_has_feature_unlikely(const unsigned long feature)
 {
 	compiletime_assert(feature < ARM64_NCAPS,
 			   "feature must be < ARM64_NCAPS");
-- 
2.37.2