linux-kernel - [RFC PATCH 02/12] riscv: add landing pad for asm routines.

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Message-Id: <20240409061043.3269676-3-debug@rivosinc.com>
Date: Mon,  8 Apr 2024 23:10:33 -0700
From: Deepak Gupta <debug@...osinc.com>
To: linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
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Subject: [RFC PATCH 02/12] riscv: add landing pad for asm routines.

SYM_* macros are used to define assembly routines. In this patch series,
re-define those macros in risc-v arch specific include file to include
a landing pad instruction at the beginning. This is done only when the
compiler flag for landing pad is enabled (i.e. __riscv_zicfilp).

Signed-off-by: Deepak Gupta <debug@...osinc.com>
---
 arch/riscv/include/asm/linkage.h | 42 ++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/arch/riscv/include/asm/linkage.h b/arch/riscv/include/asm/linkage.h
index 9e88ba23cd2b..bb43ae7dadeb 100644
--- a/arch/riscv/include/asm/linkage.h
+++ b/arch/riscv/include/asm/linkage.h
@@ -6,7 +6,49 @@
 #ifndef _ASM_RISCV_LINKAGE_H
 #define _ASM_RISCV_LINKAGE_H
 
+#ifdef __ASSEMBLY__
+#include <asm/assembler.h>
+#endif
+
 #define __ALIGN		.balign 4
 #define __ALIGN_STR	".balign 4"
 
+#ifdef __riscv_zicfilp
+/*
+ * A landing pad instruction is needed at start of asm routines
+ * re-define macros for asm routines to have a landing pad at
+ * the beginning of function. Currently use label value of 0x1.
+ * Eventually, label should be calculated as a hash over function
+ * signature.
+ */
+#define SYM_FUNC_START(name)				\
+	SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN)	\
+	lpad 0x1;
+
+#define SYM_FUNC_START_NOALIGN(name)			\
+	SYM_START(name, SYM_L_GLOBAL, SYM_A_NONE)	\
+	lpad 0x1;
+
+#define SYM_FUNC_START_LOCAL(name)			\
+	SYM_START(name, SYM_L_LOCAL, SYM_A_ALIGN)	\
+	lpad 0x1;
+
+#define SYM_FUNC_START_LOCAL_NOALIGN(name)		\
+	SYM_START(name, SYM_L_LOCAL, SYM_A_NONE)	\
+	lpad 0x1;
+
+#define SYM_FUNC_START_WEAK(name)			\
+	SYM_START(name, SYM_L_WEAK, SYM_A_ALIGN)	\
+	lpad 0x1;
+
+#define SYM_FUNC_START_WEAK_NOALIGN(name)		\
+	SYM_START(name, SYM_L_WEAK, SYM_A_NONE)		\
+	lpad 0x1;
+
+#define SYM_TYPED_FUNC_START(name)				\
+	SYM_TYPED_START(name, SYM_L_GLOBAL, SYM_A_ALIGN)	\
+	lpad 0x1;
+
+#endif
+
 #endif /* _ASM_RISCV_LINKAGE_H */
-- 
2.43.2