[RFC PATCH v1 06/16] unwind_user: Enable archs that define CFA = SP_callsite + offset

@@ -8,6 +8,7 @@
 	.cfa_off	= (s32)sizeof(long) *  2,				\
 	.ra_off		= (s32)sizeof(long) * -1,				\
 	.fp_off		= (s32)sizeof(long) * -2,				\
+	.sp_val_off	= (s32)0,						\
 	.use_fp		= true,
 
 #ifdef CONFIG_IA32_EMULATION

@@ -16,6 +17,7 @@
 	.cfa_off	= (s32)sizeof(u32)  *  2,				\
 	.ra_off		= (s32)sizeof(u32)  * -1,				\
 	.fp_off		= (s32)sizeof(u32)  * -2,				\
+	.sp_val_off	= (s32)0,						\
 	.use_fp		= true,
 
 #define in_compat_mode(regs) !user_64bit_mode(regs)

@@ -60,6 +60,7 @@ mandatory-y += topology.h
 mandatory-y += trace_clock.h
 mandatory-y += uaccess.h
 mandatory-y += unwind_user.h
+mandatory-y += unwind_user_sframe.h
 mandatory-y += unwind_user_types.h
 mandatory-y += vermagic.h
 mandatory-y += vga.h

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_UNWIND_USER_SFRAME_H
+#define _ASM_GENERIC_UNWIND_USER_SFRAME_H
+
+#include <linux/types.h>
+
+/**
+ * generic_sframe_sp_val_off - Get generic SP value offset from CFA.
+ *
+ * During unwinding the stack pointer (SP) at call site can be derived
+ * from the Canonical Frame Address (CFA) as follows:
+ *
+ *   SP = CFA + SP_val_off
+ *
+ * Most architectures define the CFA as value of SP at call site, as
+ * suggested by DWARF. For those architectures the SP value offset
+ * from CFA is 0, so that the SP at call site computes as:
+ *
+ *   SP = CFA
+ *
+ * Returns the generic SP value offset from CFA of 0.
+ */
+static inline s32 generic_sframe_sp_val_off(void)
+{
+	return 0;
+}
+
+#define sframe_sp_val_off generic_sframe_sp_val_off
+
+#endif /* _ASM_GENERIC_UNWIND_USER_SFRAME_H */

@@ -25,6 +25,7 @@ struct unwind_user_frame {
 	s32 cfa_off;
 	s32 ra_off;
 	s32 fp_off;
+	s32 sp_val_off;
 	bool use_fp;
 };
 

@@ -12,6 +12,7 @@
 #include <linux/mm.h>
 #include <linux/string_helpers.h>
 #include <linux/sframe.h>
+#include <asm/unwind_user_sframe.h>
 #include <linux/unwind_user_types.h>
 
 #include "sframe.h"

@@ -313,6 +314,7 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 	frame->ra_off  = fre->ra_off;
 	frame->fp_off  = fre->fp_off;
 	frame->use_fp  = SFRAME_FRE_CFA_BASE_REG_ID(fre->info) == SFRAME_BASE_REG_FP;
+	frame->sp_val_off = sframe_sp_val_off();
 
 	return 0;
 }

@@ -52,7 +52,7 @@ static int unwind_user_next(struct unwind_user_state *state)
 {
 	struct unwind_user_frame *frame;
 	struct unwind_user_frame _frame;
-	unsigned long cfa = 0, fp, ra = 0;
+	unsigned long cfa = 0, sp, fp, ra = 0;
 	unsigned int shift;
 
 	if (state->done)

@@ -84,8 +84,10 @@ static int unwind_user_next(struct unwind_user_state *state)
 	}
 	cfa += frame->cfa_off;
 
+	/* Get the Stack Pointer (SP) */
+	sp = cfa + frame->sp_val_off;
 	/* Make sure that stack is not going in wrong direction */
-	if (cfa <= state->sp)
+	if (sp <= state->sp)
 		goto done;
 
 	/* Make sure that the address is word aligned */

@@ -102,7 +104,7 @@ static int unwind_user_next(struct unwind_user_state *state)
 		goto done;
 
 	state->ip = ra;
-	state->sp = cfa;
+	state->sp = sp;
 	if (frame->fp_off)
 		state->fp = fp;