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RISC-V: selftests: cbo: Ensure asm operands match constraints

PATCH Applied Andrew Jones 2 participants 2 messages Jan 17, 2024 – Jan 20, 2024

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Andrew Jones

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PATCH 1/1 RISC-V: selftests: cbo: Ensure asm operands match constraints

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 <[email protected]>
Closes https://lore.kernel.org/all/[email protected] open here
Fixes a29e2a48afe3 ("RISC-V: selftests: Add CBO tests")
Signed-off-by Andrew Jones <[email protected]>
---
 tools/testing/selftests/riscv/hwprobe/cbo.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)
tools/testing/selftests/riscv/hwprobe/cbo.c +8 -10
index c6a83ab11e22..c537d52fafc5 100644
@@ -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); }
Signature · 7 lines
2.43.0


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CI Applied
#1 lore raw
This patch was applied to riscv/linux.git (fixes) by Palmer Dabbelt <[email protected]>:

Hello:

This patch was applied to riscv/linux.git (fixes)
by Palmer Dabbelt <[email protected]>:

Quoted 8 lines · 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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