[PATCH] RISC-V: selftests: cbo: Ensure asm operands match constraints

[PATCH] RISC-V: selftests: cbo: Ensure asm operands match constraints

[Andrew Jones]

The 'i' constraint expects a constant operand, which fn and its
constant derivative MK_CBO(fn) are, but passing fn through a function
as a parameter and using a local variable for MK_CBO(fn) allow the
compiler to lose sight of that when no optimization is done. Use
a macro instead of a function and skip the local variable to ensure
the compiler uses constants, matching the asm constraints.

Reported-by: Yunhui Cui <cuiyunhui@bytedance.com>
Closes: https://lore.kernel.org/all/20240117082514.42967-1-cuiyunhui@bytedance.com
Fixes: a29e2a48afe3 ("RISC-V: selftests: Add CBO tests")
Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
---
 tools/testing/selftests/riscv/hwprobe/cbo.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/riscv/hwprobe/cbo.c b/tools/testing/selftests/riscv/hwprobe/cbo.c
index c6a83ab11e22..c537d52fafc5 100644
--- a/tools/testing/selftests/riscv/hwprobe/cbo.c
+++ b/tools/testing/selftests/riscv/hwprobe/cbo.c
@@ -36,16 +36,14 @@ static void sigill_handler(int sig, siginfo_t *info, void *context)
 	regs[0] += 4;
 }
 
-static void cbo_insn(char *base, int fn)
-{
-	uint32_t insn = MK_CBO(fn);
-
-	asm volatile(
-	"mv	a0, %0\n"
-	"li	a1, %1\n"
-	".4byte	%2\n"
-	: : "r" (base), "i" (fn), "i" (insn) : "a0", "a1", "memory");
-}
+#define cbo_insn(base, fn)							\
+({										\
+	asm volatile(								\
+	"mv	a0, %0\n"							\
+	"li	a1, %1\n"							\
+	".4byte	%2\n"								\
+	: : "r" (base), "i" (fn), "i" (MK_CBO(fn)) : "a0", "a1", "memory");	\
+})
 
 static void cbo_inval(char *base) { cbo_insn(base, 0); }
 static void cbo_clean(char *base) { cbo_insn(base, 1); }
-- 
2.43.0


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Re: [PATCH] RISC-V: selftests: cbo: Ensure asm operands match constraints

[patchwork-bot+linux-riscv]

Hello:

This patch was applied to riscv/linux.git (fixes)
by Palmer Dabbelt <palmer@rivosinc.com>:

On Wed, 17 Jan 2024 14:09:34 +0100 you wrote:
> The 'i' constraint expects a constant operand, which fn and its
> constant derivative MK_CBO(fn) are, but passing fn through a function
> as a parameter and using a local variable for MK_CBO(fn) allow the
> compiler to lose sight of that when no optimization is done. Use
> a macro instead of a function and skip the local variable to ensure
> the compiler uses constants, matching the asm constraints.
> 
> [...]

Here is the summary with links:
  - RISC-V: selftests: cbo: Ensure asm operands match constraints
    https://git.kernel.org/riscv/c/0de65288d75f

You are awesome, thank you!
-- 
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