Hi,
On 01/26/2016 12:26 AM, Torsten Duwe wrote:
The gcc switch -mprofile-kernel, available for ppc64 on gcc > 4.8.5,
allows to call _mcount very early in the function, which low-level
ASM code and code patching functions need to consider.
Especially the link register and the parameter registers are still
alive and not yet saved into a new stack frame.
I'm thinking of implementing live patch support *for arm64*, and as part of
those efforts, we are proposing[1] a new *generic* gcc option, -fprolog-add=N.
This option will insert N nop instructions at the beginning of each function.
So we have to initialize those codes at the boot time to later utilize
them for FTRACE_WITH_REGS. Other than that, it will work similarly
with -mfentry on x86 (and -mprofile-kernel?).
I'm totally unfamiliar with ppc architecture, but just wondering
whether this option will also be useful for other architectures.
I will really appreciate you if you share your thoughts with me, please?
[1] https://gcc.gnu.org/ml/gcc/2015-05/msg00267.html, and
https://gcc.gnu.org/ml/gcc/2015-10/msg00090.html
Thanks,
-Takahiro AKASHI
Signed-off-by: Torsten Duwe <duwe@xxxxxxx>
---
arch/powerpc/kernel/entry_64.S | 45 +++++++++++++++++++++++++++++++++++++++--
arch/powerpc/kernel/ftrace.c | 12 +++++++++--
arch/powerpc/kernel/module_64.c | 14 +++++++++++++
3 files changed, 67 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index a94f155..e7cd043 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -1206,7 +1206,12 @@ _GLOBAL(enter_prom)
#ifdef CONFIG_DYNAMIC_FTRACE
_GLOBAL(mcount)
_GLOBAL(_mcount)
- blr
+ std r0,LRSAVE(r1) /* gcc6 does this _after_ this call _only_ */
+ mflr r0
+ mtctr r0
+ ld r0,LRSAVE(r1)
+ mtlr r0
+ bctr
_GLOBAL_TOC(ftrace_caller)
/* Taken from output of objdump from lib64/glibc */
@@ -1262,13 +1267,28 @@ _GLOBAL(ftrace_stub)
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
_GLOBAL(ftrace_graph_caller)
+#ifdef CC_USING_MPROFILE_KERNEL
+ /* with -mprofile-kernel, parameter regs are still alive at _mcount */
+ std r10, 104(r1)
+ std r9, 96(r1)
+ std r8, 88(r1)
+ std r7, 80(r1)
+ std r6, 72(r1)
+ std r5, 64(r1)
+ std r4, 56(r1)
+ std r3, 48(r1)
+ mfctr r4 /* ftrace_caller has moved local addr here */
+ std r4, 40(r1)
+ mflr r3 /* ftrace_caller has restored LR from stack */
+#else
/* load r4 with local address */
ld r4, 128(r1)
- subi r4, r4, MCOUNT_INSN_SIZE
/* Grab the LR out of the caller stack frame */
ld r11, 112(r1)
ld r3, 16(r11)
+#endif
+ subi r4, r4, MCOUNT_INSN_SIZE
bl prepare_ftrace_return
nop
@@ -1277,6 +1297,26 @@ _GLOBAL(ftrace_graph_caller)
* prepare_ftrace_return gives us the address we divert to.
* Change the LR in the callers stack frame to this.
*/
+
+#ifdef CC_USING_MPROFILE_KERNEL
+ mtlr r3
+
+ ld r0, 40(r1)
+ mtctr r0
+ ld r10, 104(r1)
+ ld r9, 96(r1)
+ ld r8, 88(r1)
+ ld r7, 80(r1)
+ ld r6, 72(r1)
+ ld r5, 64(r1)
+ ld r4, 56(r1)
+ ld r3, 48(r1)
+
+ addi r1, r1, 112
+ mflr r0
+ std r0, LRSAVE(r1)
+ bctr
+#else
ld r11, 112(r1)
std r3, 16(r11)
@@ -1284,6 +1324,7 @@ _GLOBAL(ftrace_graph_caller)
mtlr r0
addi r1, r1, 112
blr
+#endif
_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..080c525 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -306,11 +306,19 @@ __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.
*/
+#ifndef CC_USING_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");
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 6838451..30f6be1 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -475,6 +475,20 @@ static unsigned long stub_for_addr(Elf64_Shdr *sechdrs,
static int restore_r2(u32 *instruction, struct module *me)
{
if (*instruction != PPC_INST_NOP) {
+#ifdef CC_USING_MPROFILE_KERNEL
+ /* -mprofile_kernel sequence starting with
+ * mflr r0 and maybe std r0, LRSAVE(r1)
+ */
+ if ((instruction[-3] == 0x7c0802a6 &&
+ instruction[-2] == 0xf8010010) ||
+ instruction[-2] == 0x7c0802a6) {
+ /* Nothing to be done here, it's an _mcount
+ * call location and r2 will have to be
+ * restored in the _mcount function.
+ */
+ return 1;
+ };
+#endif
pr_err("%s: Expect noop after relocate, got %08x\n",
me->name, *instruction);
return 0;
--
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