From bbe8195bfad620e01a7b1cfdb0de3e4b65a72949 Mon Sep 17 00:00:00 2001
From: Christos Margiolis <christos@FreeBSD.org>
Date: Fri, 15 Sep 2023 16:33:41 +0100
Subject: [PATCH] kinst: do not look for a function epilogue

kinst currently only traces functions that start and end with the usual
function prologue and epilogue respectively. Ignoring functions that do
not have an epilogue however, makes the filtering too strict, as this
means that we can not trace functions that never return (e.g
vnlru_proc()). This patch relaxes the filtering and only checks whether
the function pushes the frame pointer.

Reviewed by:	markj
Approved by:	markj
Differential Revision:	https://reviews.freebsd.org/D41876
---
 sys/cddl/dev/kinst/amd64/kinst_isa.c | 18 ++++++++++--------
 sys/cddl/dev/kinst/riscv/kinst_isa.c | 11 +++++------
 2 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/sys/cddl/dev/kinst/amd64/kinst_isa.c b/sys/cddl/dev/kinst/amd64/kinst_isa.c
index 398f30a281c..b1d3d8727ea 100644
--- a/sys/cddl/dev/kinst/amd64/kinst_isa.c
+++ b/sys/cddl/dev/kinst/amd64/kinst_isa.c
@@ -22,7 +22,6 @@
 #include "kinst.h"
 
 #define KINST_PUSHL_RBP		0x55
-#define KINST_POPL_RBP		0x5d
 #define KINST_STI		0xfb
 #define KINST_POPF		0x9d
 
@@ -502,7 +501,7 @@ kinst_make_probe(linker_file_t lf, int symindx, linker_symval_t *symval,
 	const char *func;
 	int error, instrsize, n, off;
 	uint8_t *instr, *limit, *tmp;
-	bool push_found, pop_found;
+	bool push_found;
 
 	pd = opaque;
 	func = symval->name;
@@ -521,17 +520,20 @@ kinst_make_probe(linker_file_t lf, int symindx, linker_symval_t *symval,
 	 * manipulations since they might correspond to exception handlers.
 	 */
 	tmp = instr;
-	push_found = pop_found = false;
+	push_found = false;
 	while (tmp < limit) {
-		if (*tmp == KINST_PUSHL_RBP)
+		/*
+		 * Checking for 'pop %rbp' as well makes the filtering too
+		 * strict as it would skip functions that never return (e.g.,
+		 * vnlru_proc()).
+		 */
+		if (*tmp == KINST_PUSHL_RBP) {
 			push_found = true;
-		else if (*tmp == KINST_POPL_RBP)
-			pop_found = true;
-		if (push_found && pop_found)
 			break;
+		}
 		tmp += dtrace_instr_size(tmp);
 	}
-	if (!push_found || !pop_found)
+	if (!push_found)
 		return (0);
 
 	n = 0;
diff --git a/sys/cddl/dev/kinst/riscv/kinst_isa.c b/sys/cddl/dev/kinst/riscv/kinst_isa.c
index 9c1f4a239f8..1fabde18971 100644
--- a/sys/cddl/dev/kinst/riscv/kinst_isa.c
+++ b/sys/cddl/dev/kinst/riscv/kinst_isa.c
@@ -448,7 +448,7 @@ kinst_make_probe(linker_file_t lf, int symindx, linker_symval_t *symval,
 	kinst_patchval_t *insn, v;
 	uint8_t *instr, *limit;
 	int instrsize, n, off;
-	bool lrsc_block, store_found, ret_found;
+	bool lrsc_block, store_found;
 
 	pd = opaque;
 	func = symval->name;
@@ -464,16 +464,15 @@ kinst_make_probe(linker_file_t lf, int symindx, linker_symval_t *symval,
 		return (0);
 
 	/* Check for the usual function prologue. */
+	store_found = false;
 	for (insn = (kinst_patchval_t *)instr;
 	    insn < (kinst_patchval_t *)limit; insn++) {
-		if (dtrace_instr_sdsp(&insn) || dtrace_instr_c_sdsp(&insn))
+		if (dtrace_instr_sdsp(&insn) || dtrace_instr_c_sdsp(&insn)) {
 			store_found = true;
-		else if (dtrace_instr_ret(&insn) || dtrace_instr_c_ret(&insn))
-			ret_found = true;
-		if (store_found && ret_found)
 			break;
+		}
 	}
-	if (!store_found || !ret_found)
+	if (!store_found)
 		return (0);
 
 	n = 0;