kinst: check for 'push %rbp' anywhere in the function

Currently kinst checks if only the first instruction is 'push %rbp',
essentially excluding functions that do push RBP, but not in the first
instruction. This patch modifies kinst to check for 'push %rbp', as
well, as a following 'pop %rbp', anywhere in the function. This behavior
also matches that of FBT.

Reviewed by:	markj
Approved by:	markj (mentor)
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D40283

sys/cddl/dev/kinst/amd64/kinst_isa.c

@@ -22,6 +22,7 @@
 #include "kinst.h"
 
 #define KINST_PUSHL_RBP		0x55
+#define KINST_POPL_RBP		0x5d
 #define KINST_STI		0xfb
 #define KINST_POPF		0x9d
 
@@ -500,7 +501,8 @@ kinst_make_probe(linker_file_t lf, int symindx, linker_symval_t *symval,
 	dtrace_kinst_probedesc_t *pd;
 	const char *func;
 	int error, instrsize, n, off;
-	uint8_t *instr, *limit;
+	uint8_t *instr, *limit, *tmp;
+	bool push_found, pop_found;
 
 	pd = opaque;
 	func = symval->name;
@@ -515,12 +517,21 @@ kinst_make_probe(linker_file_t lf, int symindx, linker_symval_t *symval,
 		return (0);
 
 	/*
-	 * Ignore functions not beginning with the usual function prologue.
+	 * Refuse to instrument functions lacking the usual frame pointer
-	 * These might correspond to exception handlers with which we should not
+	 * manipulations since they might correspond to exception handlers.
-	 * meddle.  This does however exclude functions which can be safely
-	 * traced, such as cpu_switch().
 	 */
-	if (*instr != KINST_PUSHL_RBP)
+	tmp = instr;
+	push_found = pop_found = false;
+	while (tmp < limit) {
+		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)
 		return (0);
 
 	n = 0;