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Subject[PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS
Date
Once gcc is enhanced to optionally generate NOPs at the beginning
of each function, like the concept proven in
https://gcc.gnu.org/ml/gcc-patches/2016-04/msg01671.html
(sans the "fprintf (... pad_size);", which spoils the data structure
for kernel use), the generated pads can nicely be used to reroute
function calls for tracing/profiling, or live patching.

The pads look like
fffffc00081335f0 <hrtimer_init>:
fffffc00081335f0: d503201f nop
fffffc00081335f4: d503201f nop
fffffc00081335f8: a9bd7bfd stp x29, x30, [sp,#-48]!
fffffc00081335fc: 910003fd mov x29, sp
[...]

This patch gets the pad locations from the compiler-generated
__prolog_pads_loc into the _mcount_loc array, and provides the
code patching functions to turn the pads at runtime into

fffffc00081335f0 mov x9, x30
fffffc00081335f4 bl 0xfffffc00080a08c0 <ftrace_caller>
fffffc00081335f8 stp x29, x30, [sp,#-48]!
fffffc00081335fc mov x29, sp

as well as an ftrace_caller that can handle these call sites.
Now ARCH_SUPPORTS_FTRACE_OPS as a benefit, and the graph caller
still works, too.

Signed-off-by: Li Bin <huawei.libin@huawei.com>
Signed-off-by: Torsten Duwe <duwe@suse.de>
---
arch/arm64/Kconfig | 1 +
arch/arm64/Makefile | 4 ++
arch/arm64/include/asm/ftrace.h | 8 ++++
arch/arm64/kernel/Makefile | 6 +--
arch/arm64/kernel/entry-ftrace.S | 89 +++++++++++++++++++++++++++++++++++++++
arch/arm64/kernel/ftrace.c | 43 +++++++++++++++++--
include/asm-generic/vmlinux.lds.h | 2 +-
include/linux/compiler.h | 4 ++
8 files changed, 150 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 5a0a691..36a0e26 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -72,6 +72,7 @@ config ARM64
select HAVE_DMA_API_DEBUG
select HAVE_DMA_CONTIGUOUS
select HAVE_DYNAMIC_FTRACE
+ select HAVE_DYNAMIC_FTRACE_WITH_REGS
select HAVE_EFFICIENT_UNALIGNED_ACCESS
select HAVE_FTRACE_MCOUNT_RECORD
select HAVE_FUNCTION_TRACER
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 648a32c..e5e335c 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -35,6 +35,10 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
KBUILD_CFLAGS += $(call cc-option, -mpc-relative-literal-loads)
KBUILD_AFLAGS += $(lseinstr)

+ifeq ($(CONFIG_DYNAMIC_FTRACE_WITH_REGS), y)
+CC_FLAGS_FTRACE := -fprolog-pad=2 -DCC_USING_PROLOG_PAD
+endif
+
ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
KBUILD_CPPFLAGS += -mbig-endian
AS += -EB
diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index caa955f..a569666 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -16,6 +16,14 @@
#define MCOUNT_ADDR ((unsigned long)_mcount)
#define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE

+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+#define ARCH_SUPPORTS_FTRACE_OPS 1
+#define REC_IP_BRANCH_OFFSET 4
+#define FTRACE_REGS_ADDR FTRACE_ADDR
+#else
+#define REC_IP_BRANCH_OFFSET 0
+#endif
+
#ifndef __ASSEMBLY__
#include <linux/compat.h>

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 2173149..c26f3f8 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -6,9 +6,9 @@ CPPFLAGS_vmlinux.lds := -DTEXT_OFFSET=$(TEXT_OFFSET)
AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
CFLAGS_armv8_deprecated.o := -I$(src)

-CFLAGS_REMOVE_ftrace.o = -pg
-CFLAGS_REMOVE_insn.o = -pg
-CFLAGS_REMOVE_return_address.o = -pg
+CFLAGS_REMOVE_ftrace.o = -pg $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_insn.o = -pg $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_return_address.o = -pg $(CC_FLAGS_FTRACE)

# Object file lists.
arm64-obj-y := debug-monitors.o entry.o irq.o fpsimd.o \
diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
index 0f03a8f..3ebe791 100644
--- a/arch/arm64/kernel/entry-ftrace.S
+++ b/arch/arm64/kernel/entry-ftrace.S
@@ -12,6 +12,8 @@
#include <linux/linkage.h>
#include <asm/ftrace.h>
#include <asm/insn.h>
+#include <asm/asm-offsets.h>
+#include <asm/assembler.h>

/*
* Gcc with -pg will put the following code in the beginning of each function:
@@ -132,6 +134,7 @@ skip_ftrace_call:
ENDPROC(_mcount)

#else /* CONFIG_DYNAMIC_FTRACE */
+#ifndef CONFIG_DYNAMIC_FTRACE_WITH_REGS
/*
* _mcount() is used to build the kernel with -pg option, but all the branch
* instructions to _mcount() are replaced to NOP initially at kernel start up,
@@ -171,6 +174,84 @@ ftrace_graph_call: // ftrace_graph_caller();

mcount_exit
ENDPROC(ftrace_caller)
+#else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
+ENTRY(_mcount)
+ mov x10, lr
+ mov lr, x9
+ ret x10
+ENDPROC(_mcount)
+
+ENTRY(ftrace_caller)
+ stp x29, x9, [sp, #-16]!
+ sub sp, sp, #S_FRAME_SIZE
+
+ stp x0, x1, [sp]
+ stp x2, x3, [sp, #16]
+ stp x4, x5, [sp, #32]
+ stp x6, x7, [sp, #48]
+ stp x8, x9, [sp, #64]
+ stp x10, x11, [sp, #80]
+ stp x12, x13, [sp, #96]
+ stp x14, x15, [sp, #112]
+ stp x16, x17, [sp, #128]
+ stp x18, x19, [sp, #144]
+ stp x20, x21, [sp, #160]
+ stp x22, x23, [sp, #176]
+ stp x24, x25, [sp, #192]
+ stp x26, x27, [sp, #208]
+ stp x28, x29, [sp, #224]
+ /* The link Register at callee entry */
+ str x9, [sp, #S_LR]
+ /* The program counter just after the ftrace call site */
+ str lr, [sp, #S_PC]
+ /* The stack pointer as it was on ftrace_caller entry... */
+ add x29, sp, #S_FRAME_SIZE+16 /* ...is also our new FP */
+ str x29, [sp, #S_SP]
+
+ adrp x0, function_trace_op
+ ldr x2, [x0, #:lo12:function_trace_op]
+ mov x1, x9 /* saved LR == parent IP */
+ sub x0, lr, #8 /* prolog pad start == IP */
+ mov x3, sp /* complete pt_regs are @sp */
+
+ .global ftrace_call
+ftrace_call:
+
+ bl ftrace_stub
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ .global ftrace_graph_call
+ftrace_graph_call: // ftrace_graph_caller();
+ nop // If enabled, this will be replaced
+ // "b ftrace_graph_caller"
+#endif
+
+ftrace_regs_return:
+ ldp x0, x1, [sp]
+ ldp x2, x3, [sp, #16]
+ ldp x4, x5, [sp, #32]
+ ldp x6, x7, [sp, #48]
+ ldp x8, x9, [sp, #64]
+ ldp x10, x11, [sp, #80]
+ ldp x12, x13, [sp, #96]
+ ldp x14, x15, [sp, #112]
+ ldp x16, x17, [sp, #128]
+ ldp x18, x19, [sp, #144]
+ ldp x20, x21, [sp, #160]
+ ldp x22, x23, [sp, #176]
+ ldp x24, x25, [sp, #192]
+ ldp x26, x27, [sp, #208]
+ ldp x28, x29, [sp, #224]
+
+ ldr x9, [sp, #S_PC]
+ ldr lr, [sp, #S_LR]
+ add sp, sp, #S_FRAME_SIZE+16
+
+ ret x9
+
+ENDPROC(ftrace_caller)
+
+#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
#endif /* CONFIG_DYNAMIC_FTRACE */

ENTRY(ftrace_stub)
@@ -206,12 +287,20 @@ ENDPROC(ftrace_stub)
* and run return_to_handler() later on its exit.
*/
ENTRY(ftrace_graph_caller)
+#ifndef CONFIG_DYNAMIC_FTRACE_WITH_REGS
mcount_get_lr_addr x0 // pointer to function's saved lr
mcount_get_pc x1 // function's pc
mcount_get_parent_fp x2 // parent's fp
bl prepare_ftrace_return // prepare_ftrace_return(&lr, pc, fp)

mcount_exit
+#else
+ add x0, sp, #S_LR /* address of (LR pointing into caller) */
+ ldr x1, [sp, #S_PC]
+ ldr x2, [sp, #232] /* caller's frame pointer */
+ bl prepare_ftrace_return
+ b ftrace_regs_return
+#endif
ENDPROC(ftrace_graph_caller)

/*
diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index ebecf9a..917065c 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -39,6 +39,12 @@ static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
if (aarch64_insn_read((void *)pc, &replaced))
return -EFAULT;

+ /* If we already have what we'll finally want,
+ * report success. This is needed on startup.
+ */
+ if (replaced == new)
+ return 0;
+
if (replaced != old)
return -EINVAL;
}
@@ -68,28 +74,59 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
*/
int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
- unsigned long pc = rec->ip;
+ unsigned long pc = rec->ip+REC_IP_BRANCH_OFFSET;
+ int ret;
u32 old, new;

+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
old = aarch64_insn_gen_nop();
+ new = 0xaa1e03e9; /* mov x9,x30 */
+ ret = ftrace_modify_code(pc-REC_IP_BRANCH_OFFSET, old, new, true);
+ if (ret)
+ return ret;
+ smp_wmb();
+#endif
new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);

return ftrace_modify_code(pc, old, new, true);
}

+int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
+ unsigned long addr)
+{
+ unsigned long pc = rec->ip+REC_IP_BRANCH_OFFSET;
+ u32 old, new;
+
+ old = aarch64_insn_gen_branch_imm(pc, old_addr, true);
+ new = aarch64_insn_gen_branch_imm(pc, addr, true);
+
+ return ftrace_modify_code(pc, old, new, true);
+}
+
/*
* Turn off the call to ftrace_caller() in instrumented function
*/
int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
unsigned long addr)
{
- unsigned long pc = rec->ip;
+ unsigned long pc = rec->ip+REC_IP_BRANCH_OFFSET;
u32 old, new;
+ int ret;
+

old = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
new = aarch64_insn_gen_nop();

- return ftrace_modify_code(pc, old, new, true);
+ ret = ftrace_modify_code(pc, old, new, true);
+ if (ret)
+ return ret;
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+ smp_wmb();
+ old = 0xaa1e03e9; /* mov x9,x30 */
+ new = aarch64_insn_gen_nop();
+ ret = ftrace_modify_code(pc-REC_IP_BRANCH_OFFSET, old, new, true);
+#endif
+ return ret;
}

void arch_ftrace_update_code(int command)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 6a67ab9..66a72b9 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -89,7 +89,7 @@
#ifdef CONFIG_FTRACE_MCOUNT_RECORD
#define MCOUNT_REC() . = ALIGN(8); \
VMLINUX_SYMBOL(__start_mcount_loc) = .; \
- *(__mcount_loc) \
+ *(__mcount_loc) *(__prolog_pads_loc) \
VMLINUX_SYMBOL(__stop_mcount_loc) = .;
#else
#define MCOUNT_REC()
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 793c082..46289c2 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -63,8 +63,12 @@ extern void __chk_io_ptr(const volatile void __iomem *);
#if defined(CC_USING_HOTPATCH) && !defined(__CHECKER__)
#define notrace __attribute__((hotpatch(0,0)))
#else
+#ifdef CC_USING_PROLOG_PAD
+#define notrace __attribute__((prolog_pad(0)))
+#else
#define notrace __attribute__((no_instrument_function))
#endif
+#endif

/* Intel compiler defines __GNUC__. So we will overwrite implementations
* coming from above header files here
--
2.6.6
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