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authorMichael Ellerman <mpe@ellerman.id.au>2016-03-03 15:26:55 +1100
committerMichael Ellerman <mpe@ellerman.id.au>2016-03-07 14:53:53 +1100
commitf17c4e01e906c568fb03a2e6c2b99e4ee4587fbf (patch)
tree57ba5fd193ac1e40cd7b1854d121b10bbbb3960c /arch/powerpc/kernel/ftrace.c
parent136cd3450af8092f30d0e289806f08ac2aeee38f (diff)
powerpc/module: Mark module stubs with a magic value
When a module is loaded, calls out to the kernel go via a stub which is generated at runtime. One of these stubs is used to call _mcount(), which is the default target of tracing calls generated by the compiler with -pg. If dynamic ftrace is enabled (which it typically is), another stub is used to call ftrace_caller(), which is the target of tracing calls when ftrace is actually active. ftrace then wants to disable the calls to _mcount() at module startup, and enable/disable the calls to ftrace_caller() when enabling/disabling tracing - all of these it does by patching the code. As part of that code patching, the ftrace code wants to confirm that the branch it is about to modify, is in fact a call to a module stub which calls _mcount() or ftrace_caller(). Currently it does that by inspecting the instructions and confirming they are what it expects. Although that works, the code to do it is pretty intricate because it requires lots of knowledge about the exact format of the stub. We can make that process easier by marking the generated stubs with a magic value, and then looking for that magic value. Altough this is not as rigorous as the current method, I believe it is sufficient in practice. Reviewed-by: Balbir Singh <bsingharora@gmail.com> Reviewed-by: Torsten Duwe <duwe@suse.de> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/kernel/ftrace.c')
-rw-r--r--arch/powerpc/kernel/ftrace.c14
1 files changed, 4 insertions, 10 deletions
diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index 44d4d8eb3c85..4505cbfd0e13 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -106,10 +106,9 @@ static int
__ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr)
{
- unsigned int op;
- unsigned long entry, ptr;
+ unsigned long entry, ptr, tramp;
unsigned long ip = rec->ip;
- void *tramp;
+ unsigned int op;
/* read where this goes */
if (probe_kernel_read(&op, (void *)ip, sizeof(int)))
@@ -122,14 +121,9 @@ __ftrace_make_nop(struct module *mod,
}
/* lets find where the pointer goes */
- tramp = (void *)find_bl_target(ip, op);
-
- pr_devel("ip:%lx jumps to %p", ip, tramp);
+ tramp = find_bl_target(ip, op);
- if (!is_module_trampoline(tramp)) {
- pr_err("Not a trampoline\n");
- return -EINVAL;
- }
+ pr_devel("ip:%lx jumps to %lx", ip, tramp);
if (module_trampoline_target(mod, tramp, &ptr)) {
pr_err("Failed to get trampoline target\n");