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Subject[PATCH v7 01/10] ppc64 (le): prepare for -mprofile-kernel
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.

* arch/powerpc/kernel/entry_64.S:
- modify the default _mcount to be prepared for such call sites
- have the ftrace_graph_caller save function arguments before
calling its C helper prepare_ftrace_return
* arch/powerpc/include/asm/code-patching.h:
- define some common macros to make things readable.
- pull the R2 stack location definition from
arch/powerpc/kernel/module_64.c
* arch/powerpc/kernel/module_64.c:
- enhance binary code examination to handle the new patterns.

Signed-off-by: Torsten Duwe <duwe@suse.de>
---
arch/powerpc/include/asm/code-patching.h | 24 ++++++++++++++++
arch/powerpc/kernel/entry_64.S | 48 +++++++++++++++++++++++++++++++-
arch/powerpc/kernel/ftrace.c | 44 ++++++++++++++++++++++-------
arch/powerpc/kernel/module_64.c | 31 +++++++++++++++++++--
4 files changed, 133 insertions(+), 14 deletions(-)

diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h
index 840a550..7820b32 100644
--- a/arch/powerpc/include/asm/code-patching.h
+++ b/arch/powerpc/include/asm/code-patching.h
@@ -99,4 +99,28 @@ static inline unsigned long ppc_global_function_entry(void *func)
#endif
}

+#ifdef CONFIG_PPC64
+/* Some instruction encodings commonly used in dynamic ftracing
+ * and function live patching:
+ */
+
+/* This must match the definition of STK_GOT in <asm/ppc_asm.h> */
+#if defined(_CALL_ELF) && _CALL_ELF == 2
+#define R2_STACK_OFFSET 24
+#else
+#define R2_STACK_OFFSET 40
+#endif
+
+/* load / store the TOC from / into the stack frame */
+#define PPC_INST_LD_TOC (PPC_INST_LD | ___PPC_RT(__REG_R2) | \
+ ___PPC_RA(__REG_R1) | R2_STACK_OFFSET)
+#define PPC_INST_STD_TOC (PPC_INST_STD | ___PPC_RS(__REG_R2) | \
+ ___PPC_RA(__REG_R1) | R2_STACK_OFFSET)
+
+/* usually preceded by a mflr r0 */
+#define PPC_INST_STD_LR (PPC_INST_STD | ___PPC_RS(__REG_R0) | \
+ ___PPC_RA(__REG_R1) | PPC_LR_STKOFF)
+
+#endif /* CONFIG_PPC64 */
+
#endif /* _ASM_POWERPC_CODE_PATCHING_H */
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 0d525ce..2a7313c 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -1143,7 +1143,10 @@ _GLOBAL(enter_prom)
#ifdef CONFIG_DYNAMIC_FTRACE
_GLOBAL(mcount)
_GLOBAL(_mcount)
- blr
+ mflr r12
+ mtctr r12
+ mtlr r0
+ bctr

_GLOBAL_TOC(ftrace_caller)
/* Taken from output of objdump from lib64/glibc */
@@ -1198,6 +1201,7 @@ _GLOBAL(ftrace_stub)
#endif /* CONFIG_DYNAMIC_FTRACE */

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+#ifndef CC_USING_MPROFILE_KERNEL
_GLOBAL(ftrace_graph_caller)
/* load r4 with local address */
ld r4, 128(r1)
@@ -1222,6 +1226,48 @@ _GLOBAL(ftrace_graph_caller)
addi r1, r1, 112
blr

+#else /* CC_USING_MPROFILE_KERNEL */
+_GLOBAL(ftrace_graph_caller)
+ /* 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 */
+ subi r4, r4, MCOUNT_INSN_SIZE
+
+ bl prepare_ftrace_return
+ nop
+
+ /*
+ * prepare_ftrace_return gives us the address we divert to.
+ * Change the LR to this.
+ */
+ 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
+#endif /* CC_USING_MPROFILE_KERNEL */
+
_GLOBAL(return_to_handler)
/* need to save return values */
std r4, -32(r1)
diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index 44d4d8e..861af90 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -287,16 +287,14 @@ int ftrace_make_nop(struct module *mod,

#ifdef CONFIG_MODULES
#ifdef CONFIG_PPC64
+/* Examine the existing instructions for __ftrace_make_call.
+ * They should effectively be a NOP, and follow formal constraints,
+ * depending on the ABI. Return false if they don't.
+ */
+#ifndef CC_USING_MPROFILE_KERNEL
static int
-__ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
+expected_nop_sequence(void *ip, unsigned int op0, unsigned int op1)
{
- unsigned int op[2];
- void *ip = (void *)rec->ip;
-
- /* read where this goes */
- if (probe_kernel_read(op, ip, sizeof(op)))
- return -EFAULT;
-
/*
* We expect to see:
*
@@ -306,8 +304,34 @@ __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 ((op[0] != 0x48000008) || ((op[1] & 0xffff0000) != 0xe8410000)) {
- pr_err("Unexpected call sequence: %x %x\n", op[0], op[1]);
+ if ((op0 != 0x48000008) || ((op1 & 0xffff0000) != 0xe8410000))
+ return 0;
+ return 1;
+}
+#else
+static int
+expected_nop_sequence(void *ip, unsigned int op0, unsigned int op1)
+{
+ /* look for patched "NOP" on ppc64 with -mprofile-kernel */
+ if (op0 != PPC_INST_NOP)
+ return 0;
+ return 1;
+}
+#endif
+
+static int
+__ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
+{
+ unsigned int op[2];
+ void *ip = (void *)rec->ip;
+
+ /* read where this goes */
+ if (probe_kernel_read(op, ip, sizeof(op)))
+ return -EFAULT;
+
+ if (!expected_nop_sequence(ip, op[0], op[1])) {
+ pr_err("Unexpected call sequence at %p: %x %x\n",
+ ip, op[0], op[1]);
return -EINVAL;
}

diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 59663af..d75a25f 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -41,7 +41,6 @@
--RR. */

#if defined(_CALL_ELF) && _CALL_ELF == 2
-#define R2_STACK_OFFSET 24

/* An address is simply the address of the function. */
typedef unsigned long func_desc_t;
@@ -73,7 +72,6 @@ static unsigned int local_entry_offset(const Elf64_Sym *sym)
return PPC64_LOCAL_ENTRY_OFFSET(sym->st_other);
}
#else
-#define R2_STACK_OFFSET 40

/* An address is address of the OPD entry, which contains address of fn. */
typedef struct ppc64_opd_entry func_desc_t;
@@ -470,17 +468,44 @@ static unsigned long stub_for_addr(Elf64_Shdr *sechdrs,
return (unsigned long)&stubs[i];
}

+#ifdef CC_USING_MPROFILE_KERNEL
+static int is_early_mcount_callsite(u32 *instruction)
+{
+ /* -mprofile-kernel sequence starting with
+ * mflr r0 and maybe std r0, LRSAVE(r1).
+ */
+ if ((instruction[-3] == PPC_INST_MFLR &&
+ instruction[-2] == PPC_INST_STD_LR) ||
+ instruction[-2] == PPC_INST_MFLR) {
+ /* Nothing to be done here, it's an _mcount
+ * call location and r2 will have to be
+ * restored in the _mcount function.
+ */
+ return 1;
+ }
+ return 0;
+}
+#else
+/* without -mprofile-kernel, mcount calls are never early */
+static int is_early_mcount_callsite(u32 *instruction)
+{
+ return 0;
+}
+#endif
+
/* We expect a noop next: if it is, replace it with instruction to
restore r2. */
static int restore_r2(u32 *instruction, struct module *me)
{
if (*instruction != PPC_INST_NOP) {
+ if (is_early_mcount_callsite(instruction))
+ return 1;
pr_err("%s: Expect noop after relocate, got %08x\n",
me->name, *instruction);
return 0;
}
/* ld r2,R2_STACK_OFFSET(r1) */
- *instruction = 0xe8410000 | R2_STACK_OFFSET;
+ *instruction = PPC_INST_LD_TOC;
return 1;
}

--
1.8.5.6
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