LoongArch: ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL

The previous patch ("function_graph: Support recording and printing
the return value of function") has laid the groundwork for the for
the funcgraph-retval, and this modification makes it available on
the LoongArch platform.

We introduce a new structure called fgraph_ret_regs for the LoongArch
platform to hold return registers and the frame pointer. We then fill
its content in the return_to_handler and pass its address to the
function ftrace_return_to_handler to record the return value.

Link: https://lkml.kernel.org/r/c5462255e435fab363895c2d7433bc0f5a140411.1680954589.git.pengdonglin@sangfor.com.cnReviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Donglin Peng <pengdonglin@sangfor.com.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

arch/loongarch/Kconfig

@@ -103,6 +103,7 @@ config LOONGARCH
 	select HAVE_FTRACE_MCOUNT_RECORD
 	select HAVE_FUNCTION_ARG_ACCESS_API
 	select HAVE_FUNCTION_ERROR_INJECTION
+	select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_TRACER
 	select HAVE_GENERIC_VDSO

arch/loongarch/include/asm/ftrace.h

@@ -100,4 +100,26 @@ __arch_ftrace_set_direct_caller(struct pt_regs *regs, unsigned long addr)
 
 #endif /* CONFIG_FUNCTION_TRACER */
 
+#ifndef __ASSEMBLY__
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+struct fgraph_ret_regs {
+	/* a0 - a1 */
+	unsigned long regs[2];
+
+	unsigned long fp;
+	unsigned long __unused;
+};
+
+static inline unsigned long fgraph_ret_regs_return_value(struct fgraph_ret_regs *ret_regs)
+{
+	return ret_regs->regs[0];
+}
+
+static inline unsigned long fgraph_ret_regs_frame_pointer(struct fgraph_ret_regs *ret_regs)
+{
+	return ret_regs->fp;
+}
+#endif /* ifdef CONFIG_FUNCTION_GRAPH_TRACER */
+#endif
+
 #endif /* _ASM_LOONGARCH_FTRACE_H */

arch/loongarch/kernel/asm-offsets.c

@@ -12,6 +12,7 @@
 #include <asm/cpu-info.h>
 #include <asm/ptrace.h>
 #include <asm/processor.h>
+#include <asm/ftrace.h>
 
 void output_ptreg_defines(void)
 {
@@ -264,7 +265,7 @@ void output_smpboot_defines(void)
 #ifdef CONFIG_HIBERNATION
 void output_pbe_defines(void)
 {
-	COMMENT(" Linux struct pbe offsets. ");
+	COMMENT("Linux struct pbe offsets.");
 	OFFSET(PBE_ADDRESS, pbe, address);
 	OFFSET(PBE_ORIG_ADDRESS, pbe, orig_address);
 	OFFSET(PBE_NEXT, pbe, next);
@@ -272,3 +273,15 @@ void output_pbe_defines(void)
 	BLANK();
 }
 #endif
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+void output_fgraph_ret_regs_defines(void)
+{
+	COMMENT("LoongArch fgraph_ret_regs offsets.");
+	OFFSET(FGRET_REGS_A0, fgraph_ret_regs, regs[0]);
+	OFFSET(FGRET_REGS_A1, fgraph_ret_regs, regs[1]);
+	OFFSET(FGRET_REGS_FP, fgraph_ret_regs, fp);
+	DEFINE(FGRET_REGS_SIZE, sizeof(struct fgraph_ret_regs));
+	BLANK();
+}
+#endif

arch/loongarch/kernel/mcount.S

@@ -79,18 +79,20 @@ SYM_FUNC_START(ftrace_graph_caller)
 SYM_FUNC_END(ftrace_graph_caller)
 
 SYM_FUNC_START(return_to_handler)
-	PTR_ADDI	sp, sp, -2 * SZREG
-	PTR_S		a0, sp, 0
-	PTR_S		a1, sp, SZREG
+	PTR_ADDI	sp, sp, -FGRET_REGS_SIZE
+	PTR_S		a0, sp, FGRET_REGS_A0
+	PTR_S		a1, sp, FGRET_REGS_A1
+	PTR_S		zero, sp, FGRET_REGS_FP
 
+	move		a0, sp
 	bl		ftrace_return_to_handler
 
 	/* Restore the real parent address: a0 -> ra */
 	move		ra, a0
 
-	PTR_L		a0, sp, 0
-	PTR_L		a1, sp, SZREG
-	PTR_ADDI	sp, sp, 2 * SZREG
+	PTR_L		a0, sp, FGRET_REGS_A0
+	PTR_L		a1, sp, FGRET_REGS_A1
+	PTR_ADDI	sp, sp, FGRET_REGS_SIZE
 	jr		ra
 SYM_FUNC_END(return_to_handler)
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */

arch/loongarch/kernel/mcount_dyn.S

@@ -136,18 +136,19 @@ SYM_CODE_END(ftrace_graph_caller)
 
 SYM_CODE_START(return_to_handler)
 	/* Save return value regs */
-	PTR_ADDI 	sp, sp, -2 * SZREG
-	PTR_S		a0, sp, 0
-	PTR_S		a1, sp, SZREG
+	PTR_ADDI	sp, sp, -FGRET_REGS_SIZE
+	PTR_S		a0, sp, FGRET_REGS_A0
+	PTR_S		a1, sp, FGRET_REGS_A1
+	PTR_S		zero, sp, FGRET_REGS_FP
 
-	move		a0, zero
+	move		a0, sp
 	bl		ftrace_return_to_handler
 	move		ra, a0
 
 	/* Restore return value regs */
-	PTR_L		a0, sp, 0
-	PTR_L		a1, sp, SZREG
-	PTR_ADDI 	sp, sp, 2 * SZREG
+	PTR_L		a0, sp, FGRET_REGS_A0
+	PTR_L		a1, sp, FGRET_REGS_A1
+	PTR_ADDI	sp, sp, FGRET_REGS_SIZE
 
 	jr		ra
 SYM_CODE_END(return_to_handler)