[PATCH -v4 9/9] tracing: add function graph tracer support for MIPS

From: Wu Zhangjin
Date: Wed Oct 21 2009 - 10:36:03 EST

The implementation of function graph tracer for MIPS is a little
different from X86.

in MIPS, gcc(with -pg) only transfer the caller's return address(at) and
the _mcount's return address(ra) to us.

move at, ra
jal _mcount

in the function is a leaf, it will no save the return address(ra):

ffffffff80101298 <au1k_wait>:
ffffffff80101298: 67bdfff0 daddiu sp,sp,-16
ffffffff8010129c: ffbe0008 sd s8,8(sp)
ffffffff801012a0: 03a0f02d move s8,sp
ffffffff801012a4: 03e0082d move at,ra
ffffffff801012a8: 0c042930 jal ffffffff8010a4c0 <_mcount>
ffffffff801012ac: 00020021 nop

so, we can hijack it directly in _mcount, but if the function is non-leaf, the
return address is saved in the stack.

ffffffff80133030 <copy_process>:
ffffffff80133030: 67bdff50 daddiu sp,sp,-176
ffffffff80133034: ffbe00a0 sd s8,160(sp)
ffffffff80133038: 03a0f02d move s8,sp
ffffffff8013303c: ffbf00a8 sd ra,168(sp)
ffffffff80133040: ffb70098 sd s7,152(sp)
ffffffff80133044: ffb60090 sd s6,144(sp)
ffffffff80133048: ffb50088 sd s5,136(sp)
ffffffff8013304c: ffb40080 sd s4,128(sp)
ffffffff80133050: ffb30078 sd s3,120(sp)
ffffffff80133054: ffb20070 sd s2,112(sp)
ffffffff80133058: ffb10068 sd s1,104(sp)
ffffffff8013305c: ffb00060 sd s0,96(sp)
ffffffff80133060: 03e0082d move at,ra
ffffffff80133064: 0c042930 jal ffffffff8010a4c0 <_mcount>
ffffffff80133068: 00020021 nop

but we can not get the exact stack address(which saved ra) directly in
_mcount, we need to search the content of at register in the stack space
or search the "s{d,w} ra, offset(sp)" instruction in the text. 'Cause we
can not prove there is only a match in the stack space, so, we search
the text instead.

as we can see, if the first instruction above "move at, ra" is "move s8,
sp"(move fp, sp), it is a leaf function, so we hijack the at register
directly via put &return_to_handler into it, and otherwise, we search
the "s{d,w} ra, offset(sp)" instruction to get the stack offset, and
then the stack address. we use the above copy_process() as an example,
we at last find "ffbf00a8", 0xa8 is the stack offset, we plus it with
s8(fp), that is the stack address, we hijack the content via writing the
&return_to_handler in.

Signed-off-by: Wu Zhangjin <wuzhangjin@xxxxxxxxx>
---
arch/mips/Kconfig | 1 +
arch/mips/kernel/ftrace.c | 192 ++++++++++++++++++++++++++++++++++++++++
arch/mips/kernel/mcount.S | 55 +++++++++++-
arch/mips/kernel/vmlinux.lds.S | 1 +
4 files changed, 248 insertions(+), 1 deletions(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 147fbbc..de690fd 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -8,6 +8,7 @@ config MIPS
select HAVE_FUNCTION_TRACE_MCOUNT_TEST
select HAVE_DYNAMIC_FTRACE
select HAVE_FTRACE_MCOUNT_RECORD
+ select HAVE_FUNCTION_GRAPH_TRACER
# Horrible source of confusion. Die, die, die ...
select EMBEDDED
select RTC_LIB if !LEMOTE_FULOONG2E
diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
index 1e44865..fddee5b 100644
--- a/arch/mips/kernel/ftrace.c
+++ b/arch/mips/kernel/ftrace.c
@@ -13,6 +13,8 @@
#include <linux/ftrace.h>

#include <asm/cacheflush.h>
+#include <asm/asm.h>
+#include <asm/asm-offsets.h>

#ifdef CONFIG_DYNAMIC_FTRACE

@@ -105,3 +107,193 @@ int __init ftrace_dyn_arch_init(void *data)
return 0;
}
#endif /* CONFIG_DYNAMIC_FTRACE */
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+
+#define JMP 0x08000000 /* jump to target directly */
+extern void ftrace_graph_call(void);
+
+int ftrace_enable_ftrace_graph_caller(void)
+{
+ unsigned long ip = (unsigned long)(&ftrace_graph_call);
+ unsigned char old[MCOUNT_INSN_SIZE], *new;
+ int ret;
+
+ /* j ftrace_stub */
+ memcpy(old, (unsigned long *)ip, MCOUNT_INSN_SIZE);
+ new = ftrace_call_replace(JMP, (unsigned long)ftrace_graph_caller);
+
+ ret = ftrace_modify_code(ip, old, new);
+
+ return ret;
+}
+
+int ftrace_disable_ftrace_graph_caller(void)
+{
+ unsigned long ip = (unsigned long)(&ftrace_graph_call);
+ unsigned char old[MCOUNT_INSN_SIZE], *new;
+ int ret;
+
+ /* j ftrace_graph_caller */
+ memcpy(old, (unsigned long *)ip, MCOUNT_INSN_SIZE);
+ new = ftrace_call_replace(JMP, (unsigned long)ftrace_stub);
+
+ ret = ftrace_modify_code(ip, old, new);
+
+ return ret;
+}
+
+#endif /* !CONFIG_DYNAMIC_FTRACE */
+
+#define S_RA (0x2fbf << 16) /* 32bit: afbf, 64bit: ffbf */
+/* This is only available when enabled -fno-omit-frame-pointer with CONFIG_FRAME_POINTER=y */
+#define MOV_FP_SP 0x03a0f021 /* 32bit: 0x03a0f021, 64bit: 0x03a0f02d */
+#define STACK_OFFSET_MASK 0xfff /* stack offset range: 0 ~ PT_SIZE(304) */
+
+unsigned long ftrace_get_parent_addr(unsigned long self_addr,
+ unsigned long parent,
+ unsigned long parent_addr,
+ unsigned long fp)
+{
+ unsigned long sp, ip, ra;
+ unsigned int code;
+
+ /* move to the instruction "move ra, at" */
+ ip = self_addr - 8;
+
+ /* search the text until finding the "move s8, sp" instruction or
+ * "s{d,w} ra, offset(sp)" instruction */
+ do {
+ ip -= 4;
+ /* read the text we want to match */
+ if (probe_kernel_read(&code, (void *)ip, 4)) {
+ WARN_ON(1);
+ panic("read the text failure\n");
+ }
+
+ /* if the first instruction above "move at, ra" is "move
+ * s8(fp), sp", means the function is a leaf */
+ if ((code & MOV_FP_SP) == MOV_FP_SP)
+ return parent_addr;
+ } while (((code & S_RA) != S_RA));
+
+ sp = fp + (code & STACK_OFFSET_MASK);
+ ra = *(unsigned long *)sp;
+
+ if (ra == parent)
+ return sp;
+ else
+ panic
+ ("failed on getting stack address of ra\n: addr: 0x%lx, code: 0x%x\n",
+ ip, code);
+}
+
+/*
+ * Hook the return address and push it in the stack of return addrs
+ * in current thread info.
+ */
+void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
+ unsigned long fp)
+{
+ unsigned long old;
+ int faulted;
+ struct ftrace_graph_ent trace;
+ unsigned long return_hooker = (unsigned long)
+ &return_to_handler;
+
+ /*
+ * Protect against fault, even if it shouldn't
+ * happen. This tool is too much intrusive to
+ * ignore such a protection.
+ *
+ * old = *parent;
+ */
+ asm volatile (
+ "1: " STR(PTR_L) " %[old], 0(%[parent])\n"
+ " li %[faulted], 0\n"
+ "2:\n"
+
+ ".section .fixup, \"ax\"\n"
+ "3: li %[faulted], 1\n"
+ " j 2b\n"
+ ".previous\n"
+
+ ".section\t__ex_table,\"a\"\n\t"
+ STR(PTR) "\t1b, 3b\n\t"
+ ".previous\n"
+
+ : [old] "=&r" (old), [faulted] "=r" (faulted)
+ : [parent] "r" (parent)
+ : "memory"
+ );
+
+ if (unlikely(faulted)) {
+ ftrace_graph_stop();
+ WARN_ON(1);
+ return;
+ }
+
+ /* The argument *parent only work for leaf function, we need to check
+ * whether the function is leaf, if not, we need to get the real stack
+ * address which stored it.
+ *
+ * and here, we must stop tracing before calling probe_kernel_read().
+ * after calling it, restart tracing. otherwise, it will hang there.*/
+ tracing_stop();
+ parent =
+ (unsigned long *)ftrace_get_parent_addr(self_addr, old,
+ (unsigned long)parent, fp);
+ tracing_start();
+
+ if (unlikely(atomic_read(&current->tracing_graph_pause)))
+ return;
+
+ /*
+ * Protect against fault, even if it shouldn't
+ * happen. This tool is too much intrusive to
+ * ignore such a protection.
+ *
+ * *parent = return_hooker;
+ */
+ asm volatile (
+ "1: " STR(PTR_S) " %[return_hooker], 0(%[parent])\n"
+ " li %[faulted], 0\n"
+ "2:\n"
+
+ ".section .fixup, \"ax\"\n"
+ "3: li %[faulted], 1\n"
+ " j 2b\n"
+ ".previous\n"
+
+ ".section\t__ex_table,\"a\"\n\t"
+ STR(PTR) "\t1b, 3b\n\t"
+ ".previous\n"
+
+ : [faulted] "=r" (faulted)
+ : [parent] "r" (parent), [return_hooker] "r" (return_hooker)
+ : "memory"
+ );
+
+ if (unlikely(faulted)) {
+ ftrace_graph_stop();
+ WARN_ON(1);
+ return;
+ }
+
+ if (ftrace_push_return_trace(old, self_addr, &trace.depth, fp) ==
+ -EBUSY) {
+ *parent = old;
+ return;
+ }
+
+ trace.func = self_addr;
+
+ /* Only trace if the calling function expects to */
+ if (!ftrace_graph_entry(&trace)) {
+ current->curr_ret_stack--;
+ *parent = old;
+ }
+}
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S
index 30637e6..356e81c 100644
--- a/arch/mips/kernel/mcount.S
+++ b/arch/mips/kernel/mcount.S
@@ -89,6 +89,14 @@ ftrace_call:
nop

MCOUNT_RESTORE_REGS
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ .globl ftrace_graph_call
+ftrace_graph_call:
+ j ftrace_stub
+ nop
+#endif
+
.globl ftrace_stub
ftrace_stub:
RETURN_BACK
@@ -106,7 +114,15 @@ NESTED(_mcount, PT_SIZE, ra)
PTR_L t1, ftrace_trace_function /* please don't use t1 later, safe? */
bne t0, t1, static_trace
nop
-
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ PTR_L t2, ftrace_graph_return
+ bne t0, t2, ftrace_graph_caller
+ nop
+ PTR_LA t0, ftrace_graph_entry_stub
+ PTR_L t2, ftrace_graph_entry
+ bne t0, t2, ftrace_graph_caller
+ nop
+#endif
j ftrace_stub
nop

@@ -125,5 +141,42 @@ ftrace_stub:

#endif /* ! CONFIG_DYNAMIC_FTRACE */

+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+
+NESTED(ftrace_graph_caller, PT_SIZE, ra)
+ MCOUNT_SAVE_REGS
+
+ PTR_LA a0, PT_R1(sp) /* arg1: &AT -> a0 */
+ move a1, ra /* arg2: next ip, selfaddr */
+ PTR_SUBU a1, MCOUNT_INSN_SIZE
+ move a2, fp /* arg3: frame pointer */
+ jal prepare_ftrace_return
+ nop
+
+ MCOUNT_RESTORE_REGS
+ RETURN_BACK
+ END(ftrace_graph_caller)
+
+ .align 2
+ .globl return_to_handler
+return_to_handler:
+ PTR_SUBU sp, PT_SIZE
+ PTR_S v0, PT_R2(sp)
+ PTR_S v1, PT_R3(sp)
+
+ jal ftrace_return_to_handler
+ nop
+
+ /* restore the real parent address: v0 -> ra */
+ move ra, v0
+
+ PTR_L v0, PT_R2(sp)
+ PTR_L v1, PT_R3(sp)
+ PTR_ADDIU sp, PT_SIZE
+
+ jr ra
+ nop
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
.set at
.set reorder
diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
index 162b299..f25df73 100644
--- a/arch/mips/kernel/vmlinux.lds.S
+++ b/arch/mips/kernel/vmlinux.lds.S
@@ -46,6 +46,7 @@ SECTIONS
SCHED_TEXT
LOCK_TEXT
KPROBES_TEXT
+ IRQENTRY_TEXT
*(.text.*)
*(.fixup)
*(.gnu.warning)
--
1.6.2.1

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