[PATCH v2 1/4] ppc64 FTRACE_WITH_REGS implementation

From: Torsten Duwe
Date: Fri Jun 19 2015 - 10:07:38 EST

Implement FTRACE_WITH_REGS for powerpc64, on ELF ABI v2.
Initial work started by Vojtech Pavlik, used with permission.

* arch/powerpc/kernel/entry_64.S:
- enhance _mcount with a stub to test
(ftrace_trace_function == &ftrace_stub)
as suggested in Documentation/trace/ftrace-design.txt
(for reference only, patched out at runtime)
- Implement an effective ftrace_caller that works from
within the kernel binary as well as from modules.
* arch/powerpc/kernel/ftrace.c:
- be prepared to deal with ppc64 ELV ABI v2, especially
calls to _mcount that result from gcc -mprofile-kernel
* arch/powerpc/kernel/module_64.c:
- do not save the TOC pointer on the trampoline when the
destination is ftrace_caller. This trampoline jump happens from
a function prologue before a new stack frame is set up, so bad
things may happen otherwise...
- relax is_module_trampoline() to recognise the modified
trampoline.

Signed-off-by: Torsten Duwe <duwe@xxxxxxx>
---
arch/powerpc/include/asm/ftrace.h | 5 +
arch/powerpc/kernel/entry_64.S | 112 +++++++++++++++++++++++++++++++-------
arch/powerpc/kernel/ftrace.c | 72 +++++++++++++++++++++---
arch/powerpc/kernel/module_64.c | 36 +++++++++++-
4 files changed, 194 insertions(+), 31 deletions(-)

diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
index e366187..6111191 100644
--- a/arch/powerpc/include/asm/ftrace.h
+++ b/arch/powerpc/include/asm/ftrace.h
@@ -46,6 +46,8 @@
extern void _mcount(void);

#ifdef CONFIG_DYNAMIC_FTRACE
+# define FTRACE_ADDR ((unsigned long)ftrace_caller+8)
+# define FTRACE_REGS_ADDR FTRACE_ADDR
static inline unsigned long ftrace_call_adjust(unsigned long addr)
{
/* reloction of mcount call site is the same as the address */
@@ -58,6 +60,9 @@ struct dyn_arch_ftrace {
#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* __ASSEMBLY__ */

+#ifdef CONFIG_DYNAMIC_FTRACE
+#define ARCH_SUPPORTS_FTRACE_OPS 1
+#endif
#endif

#if defined(CONFIG_FTRACE_SYSCALLS) && defined(CONFIG_PPC64) && !defined(__ASSEMBLY__)
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index d180caf..a4132ef 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -1152,32 +1152,107 @@ _GLOBAL(enter_prom)

#ifdef CONFIG_FUNCTION_TRACER
#ifdef CONFIG_DYNAMIC_FTRACE
-_GLOBAL(mcount)
+
+#define TOCSAVE 24
+
_GLOBAL(_mcount)
- blr
+ nop // REQUIRED for ftrace, to calculate local/global entry diff
+ .localentry _mcount,.-_mcount
+ mflr r0
+ mtctr r0
+
+ LOAD_REG_ADDR_PIC(r12,ftrace_trace_function)
+ ld r12,0(r12)
+ LOAD_REG_ADDR_PIC(r0,ftrace_stub)
+ cmpd r0,r12
+ ld r0,LRSAVE(r1)
+ bne- 2f
+
+ mtlr r0
+ bctr
+
+2: /* here we have (*ftrace_trace_function)() in r12,
+ "selfpc" in CTR
+ and "frompc" in r0 */
+
+ mtlr r0
+ bctr
+
+_GLOBAL(ftrace_caller)
+ mr r0,r2 // global (module) call: save module TOC
+ b 1f
+ .localentry ftrace_caller,.-ftrace_caller
+ mr r0,r2 // local call: callee's TOC == our TOC
+ b 2f
+
+1: addis r2,r12,(.TOC.-0b)@ha
+ addi r2,r2,(.TOC.-0b)@l
+
+2: // Here we have our proper TOC ptr in R2,
+ // and the one we need to restore on return in r0.
+
+ ld r12, 16(r1) // get caller's address
+
+ stdu r1,-SWITCH_FRAME_SIZE(r1)
+
+ std r12, _LINK(r1)
+ SAVE_8GPRS(0,r1)
+ std r0,TOCSAVE(r1)
+ SAVE_8GPRS(8,r1)
+ SAVE_8GPRS(16,r1)
+ SAVE_8GPRS(24,r1)
+
+
+ LOAD_REG_IMMEDIATE(r3,function_trace_op)
+ ld r5,0(r3)
+
+ mflr r3
+ std r3, _NIP(r1)
+ std r3, 16(r1)
+ subi r3, r3, MCOUNT_INSN_SIZE
+ mfmsr r4
+ std r4, _MSR(r1)
+ mfctr r4
+ std r4, _CTR(r1)
+ mfxer r4
+ std r4, _XER(r1)
+ mr r4, r12
+ addi r6, r1 ,STACK_FRAME_OVERHEAD

-_GLOBAL_TOC(ftrace_caller)
- /* Taken from output of objdump from lib64/glibc */
- mflr r3
- ld r11, 0(r1)
- stdu r1, -112(r1)
- std r3, 128(r1)
- ld r4, 16(r11)
- subi r3, r3, MCOUNT_INSN_SIZE
.globl ftrace_call
ftrace_call:
bl ftrace_stub
nop
+
+ ld r3, _NIP(r1)
+ mtlr r3
+
+ REST_8GPRS(0,r1)
+ REST_8GPRS(8,r1)
+ REST_8GPRS(16,r1)
+ REST_8GPRS(24,r1)
+
+ addi r1, r1, SWITCH_FRAME_SIZE
+
+ ld r12, 16(r1) // get caller's address
+ mr r2,r0 // restore callee's TOC
+ mflr r0 // move this LR to CTR
+ mtctr r0
+ mr r0,r12 // restore callee's lr at _mcount site
+ mtlr r0
+ bctr // jump after _mcount site
+
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
.globl ftrace_graph_call
ftrace_graph_call:
b ftrace_graph_stub
_GLOBAL(ftrace_graph_stub)
#endif
- ld r0, 128(r1)
- mtlr r0
- addi r1, r1, 112
+
_GLOBAL(ftrace_stub)
+ nop
+ nop
+ .localentry ftrace_stub,.-ftrace_stub
blr
#else
_GLOBAL_TOC(_mcount)
@@ -1211,12 +1286,12 @@ _GLOBAL(ftrace_stub)
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
_GLOBAL(ftrace_graph_caller)
/* load r4 with local address */
- ld r4, 128(r1)
+ ld r4, LRSAVE+SWITCH_FRAME_SIZE(r1)
subi r4, r4, MCOUNT_INSN_SIZE

/* Grab the LR out of the caller stack frame */
- ld r11, 112(r1)
- ld r3, 16(r11)
+ ld r11, SWITCH_FRAME_SIZE(r1)
+ ld r3, LRSAVE(r11)

bl prepare_ftrace_return
nop
@@ -1228,10 +1303,7 @@ _GLOBAL(ftrace_graph_caller)
ld r11, 112(r1)
std r3, 16(r11)

- ld r0, 128(r1)
- mtlr r0
- addi r1, r1, 112
- blr
+ b ftrace_graph_stub

_GLOBAL(return_to_handler)
/* need to save return values */
diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index 44d4d8e..349d07c 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -61,8 +61,11 @@ ftrace_modify_code(unsigned long ip, unsigned int old, unsigned int new)
return -EFAULT;

/* Make sure it is what we expect it to be */
- if (replaced != old)
+ if (replaced != old) {
+ pr_err("%p: replaced (%#x) != old (%#x)",
+ (void *)ip, replaced, old);
return -EINVAL;
+ }

/* replace the text with the new text */
if (patch_instruction((unsigned int *)ip, new))
@@ -106,14 +109,16 @@ static int
__ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr)
{
- unsigned int op;
+ unsigned int op, op0, op1, pop;
unsigned long entry, ptr;
unsigned long ip = rec->ip;
void *tramp;

/* read where this goes */
- if (probe_kernel_read(&op, (void *)ip, sizeof(int)))
+ if (probe_kernel_read(&op, (void *)ip, sizeof(int))) {
+ pr_err("Fetching opcode failed.\n");
return -EFAULT;
+ }

/* Make sure that that this is still a 24bit jump */
if (!is_bl_op(op)) {
@@ -158,10 +163,46 @@ __ftrace_make_nop(struct module *mod,
*
* Use a b +8 to jump over the load.
*/
- op = 0x48000008; /* b +8 */

- if (patch_instruction((unsigned int *)ip, op))
+ pop = 0x48000008; /* b +8 */
+
+ /*
+ * 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 (probe_kernel_read(&op, (void *)(ip+4), MCOUNT_INSN_SIZE)) {
+ pr_err("Fetching op failed.\n");
+ return -EFAULT;
+ }
+
+ if (op != 0xe8410028) { /* ld r2,STACK_OFFSET(r1) */
+
+ if (probe_kernel_read(&op0, (void *)(ip-8), MCOUNT_INSN_SIZE)) {
+ pr_err("Fetching op0 failed.\n");
+ return -EFAULT;
+ }
+
+ if (probe_kernel_read(&op1, (void *)(ip-4), MCOUNT_INSN_SIZE)) {
+ pr_err("Fetching op1 failed.\n");
+ return -EFAULT;
+ }
+
+ /* mflr r0 ; std r0,LRSAVE(r1) */
+ if (op0 != 0x7c0802a6 && op1 != 0xf8010010) {
+ pr_err("Unexpected instructions around bl\n"
+ "when enabling dynamic ftrace!\t"
+ "(%08x,%08x,bl,%08x)\n", op0, op1, op);
+ return -EINVAL;
+ }
+
+ /* When using -mkernel_profile there is no load to jump over */
+ pop = PPC_INST_NOP;
+ }
+
+ if (patch_instruction((unsigned int *)ip, pop)) {
+ pr_err("Patching NOP failed.\n");
return -EPERM;
+ }

return 0;
}
@@ -287,6 +324,13 @@ int ftrace_make_nop(struct module *mod,

#ifdef CONFIG_MODULES
#ifdef CONFIG_PPC64
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
+ unsigned long addr)
+{
+ return ftrace_make_call(rec, addr);
+}
+#endif
static int
__ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
@@ -306,11 +350,19 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
* The load offset is different depending on the ABI. For simplicity
* just mask it out when doing the compare.
*/
+#if 0 /* -pg, no -mprofile-kernel */
if ((op[0] != 0x48000008) || ((op[1] & 0xffff0000) != 0xe8410000)) {
- pr_err("Unexpected call sequence: %x %x\n", op[0], op[1]);
+ pr_err("Unexpected call sequence at %p: %x %x\n",
+ ip, op[0], op[1]);
return -EINVAL;
}
-
+#else
+ /* look for patched "NOP" on ppc64 with -mprofile-kernel */
+ if (op[0] != 0x60000000) {
+ pr_err("Unexpected call at %p: %x\n", ip, op[0]);
+ return -EINVAL;
+ }
+#endif
/* If we never set up a trampoline to ftrace_caller, then bail */
if (!rec->arch.mod->arch.tramp) {
pr_err("No ftrace trampoline\n");
@@ -330,7 +381,7 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)

return 0;
}
-#else
+#else /* !CONFIG_PPC64: */
static int
__ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 6838451..1428ad8 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -138,12 +138,21 @@ static u32 ppc64_stub_insns[] = {
0x4e800420 /* bctr */
};

+/* In case of _mcount calls or dynamic ftracing, Do not save the
+ current callee's TOC (in R2) again into the original caller's stack
+ frame during this trampoline hop. The stack frame already holds
+ that of the original caller. _mcount and ftrace_caller will take
+ care of this TOC value themselves.
+*/
+#define SQUASH_TOC_SAVE_INSN(trampoline_addr) \
+ (((struct ppc64_stub_entry *)(trampoline_addr))->jump[2] = PPC_INST_NOP)
+
#ifdef CONFIG_DYNAMIC_FTRACE

static u32 ppc64_stub_mask[] = {
0xffff0000,
0xffff0000,
- 0xffffffff,
+ 0x00000000,
0xffffffff,
#if !defined(_CALL_ELF) || _CALL_ELF != 2
0xffffffff,
@@ -170,6 +180,9 @@ bool is_module_trampoline(u32 *p)
if ((insna & mask) != (insnb & mask))
return false;
}
+ if (insns[2] != ppc64_stub_insns[2] &&
+ insns[2] != PPC_INST_NOP)
+ return false;

return true;
}
@@ -475,6 +488,17 @@ static unsigned long stub_for_addr(Elf64_Shdr *sechdrs,
static int restore_r2(u32 *instruction, struct module *me)
{
if (*instruction != PPC_INST_NOP) {
+
+ /* -mprofile_kernel sequence starting with
+ mflr r0; std r0, LRSAVE(r1) */
+ if (instruction[-3] == 0x7c0802a6 &&
+ instruction[-2] == 0xf8010010) {
+ /* Nothing to be done here, it's an _mcount
+ call location and r2 will have to be restored
+ in the _mcount function */
+ return 2;
+ };
+
pr_err("%s: Expect noop after relocate, got %08x\n",
me->name, *instruction);
return 0;
@@ -490,7 +511,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
unsigned int relsec,
struct module *me)
{
- unsigned int i;
+ unsigned int i, r2;
Elf64_Rela *rela = (void *)sechdrs[relsec].sh_addr;
Elf64_Sym *sym;
unsigned long *location;
@@ -603,8 +624,12 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
value = stub_for_addr(sechdrs, value, me);
if (!value)
return -ENOENT;
- if (!restore_r2((u32 *)location + 1, me))
+ r2 = restore_r2((u32 *)location + 1, me);
+ if (!r2)
return -ENOEXEC;
+ /* Squash the TOC saver for profiler calls */
+ if (!strcmp("_mcount", strtab+sym->st_name))
+ SQUASH_TOC_SAVE_INSN(value);
} else
value += local_entry_offset(sym);

@@ -665,6 +689,9 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
me->arch.tramp = stub_for_addr(sechdrs,
(unsigned long)ftrace_caller,
me);
+ /* ftrace_caller will take care of the TOC;
+ do not clobber original caller's value. */
+ SQUASH_TOC_SAVE_INSN(me->arch.tramp);
#endif

return 0;
--
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