linux-kernel - [PATCH v2] riscv: lib: Check if output in asm goto supported

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Message-Id: <20240118-csum_remove_output_operands_asm_goto-v2-1-5d1b73cf93d4@rivosinc.com>
Date: Thu, 18 Jan 2024 14:36:45 -0800
From: Charlie Jenkins <charlie@...osinc.com>
To: Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 Charlie Jenkins <charlie@...osinc.com>
Subject: [PATCH v2] riscv: lib: Check if output in asm goto supported

The output field of an asm goto statement is not supported by all
compilers. If it is not supported, fallback to the non-optimized code.

Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
Fixes: a04c192eabfb ("riscv: Add checksum library")
---
The OutputOperands field for asm goto statements is only supported
starting from GCC 11. Split the asm goto to remove the use of this
feature.
---
Changes in v2:
- Use CC_HAS_ASM_GOTO_TIED_OUTPUT
- Link to v1: https://lore.kernel.org/r/20240118-csum_remove_output_operands_asm_goto-v1-1-47c672bb9d4b@rivosinc.com
---
 arch/riscv/lib/csum.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/riscv/lib/csum.c b/arch/riscv/lib/csum.c
index 06ce8e7250d9..af3df5274ccb 100644
--- a/arch/riscv/lib/csum.c
+++ b/arch/riscv/lib/csum.c
@@ -156,6 +156,7 @@ do_csum_with_alignment(const unsigned char *buff, int len)
 	end = (const unsigned long *)(buff + len);
 	csum = do_csum_common(ptr, end, data);
 
+#ifdef CC_HAS_ASM_GOTO_TIED_OUTPUT
 	/*
 	 * Zbb support saves 6 instructions, so not worth checking without
 	 * alternatives if supported
@@ -214,6 +215,7 @@ do_csum_with_alignment(const unsigned char *buff, int len)
 		return csum >> 16;
 	}
 no_zbb:
+#endif /* CC_HAS_ASM_GOTO_TIED_OUTPUT */
 #ifndef CONFIG_32BIT
 	csum += ror64(csum, 32);
 	csum >>= 32;

---
base-commit: 080c4324fa5e81ff3780206a138223abfb57a68e
change-id: 20240118-csum_remove_output_operands_asm_goto-49922c141ce7
-- 
- Charlie