[RFC PATCH 10/15] powerpc/ftrace: Simplify ftrace_make_nop()
Naveen N Rao
naveen at kernel.org
Thu Jun 8 02:55:25 AEST 2023
Now that we validate the ftrace location during initialization in
ftrace_init_nop(), we can simplify ftrace_make_nop() to patch-in the nop
without worrying about the instructions surrounding the ftrace location.
Note that we continue to ensure that we have a bl to
ftrace_[regs_]caller at the ftrace location before nop-ing it out.
Signed-off-by: Naveen N Rao <naveen at kernel.org>
---
arch/powerpc/kernel/trace/ftrace.c | 220 +++++------------------------
1 file changed, 32 insertions(+), 188 deletions(-)
diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index c0d185742c23ca..67773cd14da71a 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -116,112 +116,6 @@ static unsigned long find_bl_target(unsigned long ip, ppc_inst_t op)
return ip + (long)offset;
}
-#ifdef CONFIG_MODULES
-static int
-__ftrace_make_nop(struct module *mod,
- struct dyn_ftrace *rec, unsigned long addr)
-{
- unsigned long entry, ptr, tramp;
- unsigned long ip = rec->ip;
- ppc_inst_t op, pop;
-
- /* read where this goes */
- if (copy_inst_from_kernel_nofault(&op, (void *)ip)) {
- pr_err("Fetching opcode failed.\n");
- return -EFAULT;
- }
-
- /* Make sure that this is still a 24bit jump */
- if (!is_bl_op(op)) {
- pr_err("Not expected bl: opcode is %08lx\n", ppc_inst_as_ulong(op));
- return -EINVAL;
- }
-
- /* lets find where the pointer goes */
- tramp = find_bl_target(ip, op);
-
- pr_devel("ip:%lx jumps to %lx", ip, tramp);
-
- if (module_trampoline_target(mod, tramp, &ptr)) {
- pr_err("Failed to get trampoline target\n");
- return -EFAULT;
- }
-
- pr_devel("trampoline target %lx", ptr);
-
- entry = ppc_global_function_entry((void *)addr);
- /* This should match what was called */
- if (ptr != entry) {
- pr_err("addr %lx does not match expected %lx\n", ptr, entry);
- return -EINVAL;
- }
-
- if (IS_ENABLED(CONFIG_MPROFILE_KERNEL)) {
- if (copy_inst_from_kernel_nofault(&op, (void *)(ip - 4))) {
- pr_err("Fetching instruction at %lx failed.\n", ip - 4);
- return -EFAULT;
- }
-
- /* We expect either a mflr r0, or a std r0, LRSAVE(r1) */
- if (!ppc_inst_equal(op, ppc_inst(PPC_RAW_MFLR(_R0))) &&
- !ppc_inst_equal(op, ppc_inst(PPC_INST_STD_LR))) {
- pr_err("Unexpected instruction %08lx around bl _mcount\n",
- ppc_inst_as_ulong(op));
- return -EINVAL;
- }
- } else if (IS_ENABLED(CONFIG_PPC64)) {
- /*
- * Check what is in the next instruction. We can see ld r2,40(r1), but
- * on first pass after boot we will see mflr r0.
- */
- if (copy_inst_from_kernel_nofault(&op, (void *)(ip + 4))) {
- pr_err("Fetching op failed.\n");
- return -EFAULT;
- }
-
- if (!ppc_inst_equal(op, ppc_inst(PPC_INST_LD_TOC))) {
- pr_err("Expected %08lx found %08lx\n", PPC_INST_LD_TOC,
- ppc_inst_as_ulong(op));
- return -EINVAL;
- }
- }
-
- /*
- * When using -mprofile-kernel or PPC32 there is no load to jump over.
- *
- * Otherwise our original call site looks like:
- *
- * bl <tramp>
- * ld r2,XX(r1)
- *
- * Milton Miller pointed out that we can not simply nop the branch.
- * If a task was preempted when calling a trace function, the nops
- * will remove the way to restore the TOC in r2 and the r2 TOC will
- * get corrupted.
- *
- * Use a b +8 to jump over the load.
- * XXX: could make PCREL depend on MPROFILE_KERNEL
- * XXX: check PCREL && MPROFILE_KERNEL calling sequence
- */
- if (IS_ENABLED(CONFIG_MPROFILE_KERNEL) || IS_ENABLED(CONFIG_PPC32))
- pop = ppc_inst(PPC_RAW_NOP());
- else
- pop = ppc_inst(PPC_RAW_BRANCH(8)); /* b +8 */
-
- if (patch_instruction((u32 *)ip, pop)) {
- pr_err("Patching NOP failed.\n");
- return -EPERM;
- }
-
- return 0;
-}
-#else
-static int __ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)
-{
- return 0;
-}
-#endif /* CONFIG_MODULES */
-
static unsigned long find_ftrace_tramp(unsigned long ip)
{
int i;
@@ -235,88 +129,6 @@ static unsigned long find_ftrace_tramp(unsigned long ip)
return 0;
}
-static int __ftrace_make_nop_kernel(struct dyn_ftrace *rec, unsigned long addr)
-{
- unsigned long tramp, ip = rec->ip;
- ppc_inst_t op;
-
- /* Read where this goes */
- if (copy_inst_from_kernel_nofault(&op, (void *)ip)) {
- pr_err("Fetching opcode failed.\n");
- return -EFAULT;
- }
-
- /* Make sure that this is still a 24bit jump */
- if (!is_bl_op(op)) {
- pr_err("Not expected bl: opcode is %08lx\n", ppc_inst_as_ulong(op));
- return -EINVAL;
- }
-
- /* Let's find where the pointer goes */
- tramp = find_bl_target(ip, op);
-
- pr_devel("ip:%lx jumps to %lx", ip, tramp);
-
- /* Are ftrace trampolines reachable? */
- if (!find_ftrace_tramp(ip)) {
- pr_err("No ftrace trampolines reachable from %ps\n", (void *)ip);
- return -EINVAL;
- }
-
- if (patch_instruction((u32 *)ip, ppc_inst(PPC_RAW_NOP()))) {
- pr_err("Patching NOP failed.\n");
- return -EPERM;
- }
-
- return 0;
-}
-
-int ftrace_make_nop(struct module *mod,
- struct dyn_ftrace *rec, unsigned long addr)
-{
- unsigned long ip = rec->ip;
- ppc_inst_t old, new;
-
- /*
- * If the calling address is more that 24 bits away,
- * then we had to use a trampoline to make the call.
- * Otherwise just update the call site.
- */
- if (test_24bit_addr(ip, addr)) {
- /* within range */
- old = ftrace_call_replace(ip, addr, 1);
- new = ppc_inst(PPC_RAW_NOP());
- return ftrace_modify_code(ip, old, new);
- } else if (core_kernel_text(ip)) {
- return __ftrace_make_nop_kernel(rec, addr);
- } else if (!IS_ENABLED(CONFIG_MODULES)) {
- return -EINVAL;
- }
-
- /*
- * Out of range jumps are called from modules.
- * We should either already have a pointer to the module
- * or it has been passed in.
- */
- if (!rec->arch.mod) {
- if (!mod) {
- pr_err("No module loaded addr=%lx\n", addr);
- return -EFAULT;
- }
- rec->arch.mod = mod;
- } else if (mod) {
- if (mod != rec->arch.mod) {
- pr_err("Record mod %p not equal to passed in mod %p\n",
- rec->arch.mod, mod);
- return -EINVAL;
- }
- /* nothing to do if mod == rec->arch.mod */
- } else
- mod = rec->arch.mod;
-
- return __ftrace_make_nop(mod, rec, addr);
-}
-
#ifdef CONFIG_MODULES
/*
* Examine the existing instructions for __ftrace_make_call.
@@ -607,6 +419,38 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
}
#endif
+int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)
+{
+ unsigned long tramp, ip = rec->ip;
+ ppc_inst_t old, new;
+
+ /* Nop-out the ftrace location */
+ new = ppc_inst(PPC_RAW_NOP());
+ if (is_offset_in_branch_range(addr - ip)) {
+ /* Within range */
+ old = ftrace_create_branch_inst(ip, addr, 1);
+ return ftrace_modify_code(ip, old, new);
+ } else if (core_kernel_text(ip)) {
+ /* We would be branching to one of our ftrace tramps */
+ tramp = find_ftrace_tramp(ip);
+ if (!tramp) {
+ pr_err("0x%lx: No ftrace trampolines reachable\n", ip);
+ return -EINVAL;
+ }
+ old = ftrace_create_branch_inst(ip, tramp, 1);
+ return ftrace_modify_code(ip, old, new);
+ } else if (IS_ENABLED(CONFIG_MODULES)) {
+ /* Module code would be going to one of the module stubs */
+ if (!mod)
+ mod = rec->arch.mod;
+ tramp = (addr == (unsigned long)ftrace_caller ? mod->arch.tramp : mod->arch.tramp_regs);
+ old = ftrace_create_branch_inst(ip, tramp, 1);
+ return ftrace_modify_code(ip, old, new);
+ }
+
+ return -EINVAL;
+}
+
int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
{
unsigned long addr, ip = rec->ip;
--
2.40.1
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