linux-kernel - [PATCH v2 14/18] riscv: alternative: Allow calls with alternate link registers

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Message-ID: <20251009015839.3460231-15-samuel.holland@sifive.com>
Date: Wed,  8 Oct 2025 18:57:50 -0700
From: Samuel Holland <samuel.holland@...ive.com>
To: Palmer Dabbelt <palmer@...belt.com>,
	Paul Walmsley <pjw@...nel.org>,
	linux-riscv@...ts.infradead.org
Cc: devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	Conor Dooley <conor@...nel.org>,
	Alexandre Ghiti <alex@...ti.fr>,
	Emil Renner Berthing <kernel@...il.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Samuel Holland <samuel.holland@...ive.com>
Subject: [PATCH v2 14/18] riscv: alternative: Allow calls with alternate link registers

Alternative assembly code may wish to use an alternate link register to
minimize the number of clobbered registers. Apply the offset fix to all
jalr (not jr) instructions, i.e. where rd is not x0.

Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
---

(no changes since v1)

 arch/riscv/kernel/alternative.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
index 7eb3cb1215c62..249ee55d05475 100644
--- a/arch/riscv/kernel/alternative.c
+++ b/arch/riscv/kernel/alternative.c
@@ -121,8 +121,8 @@ void riscv_alternative_fix_offsets(void *alt_ptr, unsigned int len,
 			if (!riscv_insn_is_jalr(insn2))
 				continue;
 
-			/* if instruction pair is a call, it will use the ra register */
-			if (RV_EXTRACT_RD_REG(insn) != 1)
+			/* if instruction pair is a call, it will save a link register */
+			if (RV_EXTRACT_RD_REG(insn) == 0)
 				continue;
 
 			riscv_alternative_fix_auipc_jalr(alt_ptr + i * sizeof(u32),
-- 
2.47.2