[RFC PATCH 2/3] powerpc/ftrace: Override ftrace_location_lookup() for MPROFILE_KERNEL
Naveen N. Rao
naveen.n.rao at linux.vnet.ibm.com
Fri Feb 11 00:58:29 AEDT 2022
Steven Rostedt wrote:
> On Wed, 09 Feb 2022 17:50:09 +0000
> "Naveen N. Rao" <naveen.n.rao at linux.vnet.ibm.com> wrote:
>
>> However, I think we will not be able to use a fixed range. I would like
>> to reserve instructions from function entry till the branch to
>> _mcount(), and it can be two or four instructions depending on whether a
>> function has a global entry point. For this, I am considering adding a
>> field in 'struct dyn_arch_ftrace', and a hook in ftrace_process_locs()
>> to initialize the same. I may need to override ftrace_cmp_recs().
>
> Be careful about adding anything to dyn_arch_ftrace. powerpc already adds
> the pointer to the module. Anything you add to that gets multiplied by
> thousands of times (which takes up memory).
>
> At boot up you may see something like:
>
> ftrace: allocating 45363 entries in 178 pages
>
> That's 45,363 dyn_arch_ftrace structures. And each module loads their own
> as well. To see how many total you have after boot up:
>
>
> # cat /sys/kernel/tracing/dyn_ftrace_total_info
> 55974 pages:295 groups: 89
>
> That's from the same kernel. Another 10,000 entries were created by modules.
> (This was for x86_64)
>
> What you may be able to do, is to add a way to look at the already saved
> kallsyms, which keeps track of the function entry and exit to know how to
> map an address back to the function.
>
> kallsyms_lookup(addr, NULL, &offset, NULL, NULL);
>
> Should give you the offset of addr from the start of the function.
Good point. I should be able to overload the existing field for this
purpose. Is something like the below ok?
---
arch/powerpc/include/asm/ftrace.h | 13 ++++++
arch/powerpc/kernel/trace/ftrace.c | 73 ++++++++++++++++++++++++++----
kernel/trace/ftrace.c | 2 +
3 files changed, 78 insertions(+), 10 deletions(-)
diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
index debe8c4f706260..96d6e26cee86af 100644
--- a/arch/powerpc/include/asm/ftrace.h
+++ b/arch/powerpc/include/asm/ftrace.h
@@ -59,6 +59,19 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
struct dyn_arch_ftrace {
struct module *mod;
};
+
+struct dyn_ftrace;
+struct module *ftrace_mod_addr_get(struct dyn_ftrace *rec);
+void ftrace_mod_addr_set(struct dyn_ftrace *rec, struct module *mod);
+
+#ifdef CONFIG_MPROFILE_KERNEL
+int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
+#define ftrace_init_nop ftrace_init_nop
+
+int ftrace_cmp_recs(const void *a, const void *b);
+#define ftrace_cmp_recs ftrace_cmp_recs
+#endif
+
#endif /* __ASSEMBLY__ */
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index 80b6285769f27c..d9b6faa4c98a8c 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -428,21 +428,21 @@ int ftrace_make_nop(struct module *mod,
* We should either already have a pointer to the module
* or it has been passed in.
*/
- if (!rec->arch.mod) {
+ if (!ftrace_mod_addr_get(rec)) {
if (!mod) {
pr_err("No module loaded addr=%lx\n", addr);
return -EFAULT;
}
- rec->arch.mod = mod;
+ ftrace_mod_addr_set(rec, mod);
} else if (mod) {
- if (mod != rec->arch.mod) {
+ if (mod != ftrace_mod_addr_get(rec)) {
pr_err("Record mod %p not equal to passed in mod %p\n",
- rec->arch.mod, mod);
+ ftrace_mod_addr_get(rec), mod);
return -EINVAL;
}
/* nothing to do if mod == rec->arch.mod */
} else
- mod = rec->arch.mod;
+ mod = ftrace_mod_addr_get(rec);
return __ftrace_make_nop(mod, rec, addr);
#else
@@ -451,6 +451,59 @@ int ftrace_make_nop(struct module *mod,
#endif /* CONFIG_MODULES */
}
+#ifdef CONFIG_MPROFILE_KERNEL
+struct module *ftrace_mod_addr_get(struct dyn_ftrace *rec)
+{
+ return (struct module *)((unsigned long)rec->arch.mod & ~0x1);
+}
+
+void ftrace_mod_addr_set(struct dyn_ftrace *rec, struct module *mod)
+{
+ rec->arch.mod = (struct module *)(((unsigned long)rec->arch.mod & 0x1) | (unsigned long)mod);
+}
+
+bool ftrace_location_has_gep(const struct dyn_ftrace *rec)
+{
+ return !!((unsigned long)rec->arch.mod & 0x1);
+}
+
+int ftrace_cmp_recs(const void *a, const void *b)
+{
+ const struct dyn_ftrace *key = a;
+ const struct dyn_ftrace *rec = b;
+ int offset = ftrace_location_has_gep(rec) ? 12 : 4;
+
+ if (key->flags < rec->ip - offset)
+ return -1;
+ if (key->ip >= rec->ip + MCOUNT_INSN_SIZE)
+ return 1;
+ return 0;
+}
+
+int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
+{
+ unsigned long offset;
+
+ if (!kallsyms_lookup_size_offset(rec->ip, NULL, &offset) || (offset != 12 && offset != 4)) {
+ /* TODO: implement logic to deduce lep/gep from code */
+ } else if (offset == 12) {
+ ftrace_mod_addr_set(rec, (struct module *)1);
+ }
+
+ return ftrace_make_nop(mod, rec, MCOUNT_ADDR);
+}
+#else
+struct module *ftrace_mod_addr_get(struct dyn_ftrace *rec)
+{
+ return rec->arch.mod;
+}
+
+void ftrace_mod_addr_set(struct dyn_ftrace *rec, struct module * mod)
+{
+ rec->arch.mod = mod;
+}
+#endif /* CONFIG_MPROFILE_KERNEL */
+
#ifdef CONFIG_MODULES
#ifdef CONFIG_PPC64
/*
@@ -494,7 +547,7 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
ppc_inst_t instr;
void *ip = (void *)rec->ip;
unsigned long entry, ptr, tramp;
- struct module *mod = rec->arch.mod;
+ struct module *mod = ftrace_mod_addr_get(rec);
/* read where this goes */
if (copy_inst_from_kernel_nofault(op, ip))
@@ -561,7 +614,7 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
int err;
ppc_inst_t op;
u32 *ip = (u32 *)rec->ip;
- struct module *mod = rec->arch.mod;
+ struct module *mod = ftrace_mod_addr_get(rec);
unsigned long tramp;
/* read where this goes */
@@ -678,7 +731,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
* Being that we are converting from nop, it had better
* already have a module defined.
*/
- if (!rec->arch.mod) {
+ if (!ftrace_mod_addr_get(rec)) {
pr_err("No module loaded\n");
return -EINVAL;
}
@@ -699,7 +752,7 @@ __ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
ppc_inst_t op;
unsigned long ip = rec->ip;
unsigned long entry, ptr, tramp;
- struct module *mod = rec->arch.mod;
+ struct module *mod = ftrace_mod_addr_get(rec);
/* If we never set up ftrace trampolines, then bail */
if (!mod->arch.tramp || !mod->arch.tramp_regs) {
@@ -814,7 +867,7 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
/*
* Out of range jumps are called from modules.
*/
- if (!rec->arch.mod) {
+ if (!ftrace_mod_addr_get(rec)) {
pr_err("No module loaded\n");
return -EINVAL;
}
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index f9feb197b2daaf..68f20cf34b0c47 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1510,6 +1510,7 @@ ftrace_ops_test(struct ftrace_ops *ops, unsigned long ip, void *regs)
}
+#ifndef ftrace_cmp_recs
static int ftrace_cmp_recs(const void *a, const void *b)
{
const struct dyn_ftrace *key = a;
@@ -1521,6 +1522,7 @@ static int ftrace_cmp_recs(const void *a, const void *b)
return 1;
return 0;
}
+#endif
static struct dyn_ftrace *lookup_rec(unsigned long start, unsigned long end)
{
Thanks,
Naveen
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