git: ea89133dbc5f - main - kinst: check for 'push %rbp' anywhere in the function

[Christos Margiolis]

The branch main has been updated by christos:

URL: 
https://cgit.FreeBSD.org/src/commit/?id=ea89133dbc5f29cbb8db48ecc09a47ea22d8aa9e

commit ea89133dbc5f29cbb8db48ecc09a47ea22d8aa9e
Author:     Christos Margiolis <chris...@freebsd.org>
AuthorDate: 2023-07-19 14:53:08 +0000
Commit:     Christos Margiolis <chris...@freebsd.org>
CommitDate: 2023-07-19 14:53:08 +0000

    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 | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/sys/cddl/dev/kinst/amd64/kinst_isa.c 
b/sys/cddl/dev/kinst/amd64/kinst_isa.c
index 908dc79e9247..398f30a281c0 100644
--- a/sys/cddl/dev/kinst/amd64/kinst_isa.c
+++ b/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.
-        * These might correspond to exception handlers with which we should not
-        * meddle.  This does however exclude functions which can be safely
-        * traced, such as cpu_switch().
+        * Refuse to instrument functions lacking the usual frame pointer
+        * manipulations since they might correspond to exception handlers.
         */
-       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;