Re: [PATCH 01/11] riscv: add landing pad for asm routines.

[Deepak Gupta <debug@rivosinc.com>]

On Fri, Jul 25, 2025 at 08:13:29AM +0200, Heinrich Schuchardt wrote:
>On 25.07.25 01:36, Deepak Gupta wrote:
>>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).
>>
>>TODO: Update `lpad 0` with `lpad %lpad_hash(name)` after toolchain
>>support.
>>
>>Signed-off-by: Deepak Gupta <debug@rivosinc.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..162774b81158 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.
>
>Your code below uses label value 0 which disables tag checking. As 
>long as we don't have tool support for calculating function hashes 
>that is an appropriate approach.
>

Yes I made the fix at other place where function prototype was determined
to be static (see `call_on_irq_stack` in entry.S)

In this patch, it wasn't possible.

>%s/Currently use label value of 0x1./Label value 0x0 disables tag checking./
>

Thanks its lingering from earlier. Will fix it.

>Best regards
>
>Heinrich
>
>>+ * 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 0;
>>+
>>+#define SYM_FUNC_START_NOALIGN(name)			\
>>+	SYM_START(name, SYM_L_GLOBAL, SYM_A_NONE)	\
>>+	lpad 0;
>>+
>>+#define SYM_FUNC_START_LOCAL(name)			\
>>+	SYM_START(name, SYM_L_LOCAL, SYM_A_ALIGN)	\
>>+	lpad 0;
>>+
>>+#define SYM_FUNC_START_LOCAL_NOALIGN(name)		\
>>+	SYM_START(name, SYM_L_LOCAL, SYM_A_NONE)	\
>>+	lpad 0;
>>+
>>+#define SYM_FUNC_START_WEAK(name)			\
>>+	SYM_START(name, SYM_L_WEAK, SYM_A_ALIGN)	\
>>+	lpad 0;
>>+
>>+#define SYM_FUNC_START_WEAK_NOALIGN(name)		\
>>+	SYM_START(name, SYM_L_WEAK, SYM_A_NONE)		\
>>+	lpad 0;
>>+
>>+#define SYM_TYPED_FUNC_START(name)				\
>>+	SYM_TYPED_START(name, SYM_L_GLOBAL, SYM_A_ALIGN)	\
>>+	lpad 0;
>>+
>>+#endif
>>+
>>  #endif /* _ASM_RISCV_LINKAGE_H */
>>
>