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Subject[PATCH -v5 10/11] tracing: add function graph tracer support for MIPS
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(Add Frederic Weisbecker <fweisbec@gmail.com> to the CC list)

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

if 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(fp), sp"(only available with -fno-omit-frame-pointer which is enabled
by CONFIG_FRAME_POINTER), it is a leaf function, so we hijack the at
register directly via putting &return_to_handler into it, 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.
(As pajko <kpajko79@gmail.com> recommend, if we enable
PROFILE_BEFORE_PROLOGUE in gcc/config/mips/mips.h, there will be no
difference between non-leaf and leaf function, we hope
PROFILE_BEFORE_PROLOGUE will be enabled by default in the future
version of gcc, so, we can remove ftrace_get_parent_addr() directly. )
Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
---
arch/mips/Kconfig | 1 +
arch/mips/kernel/ftrace.c | 93 +++++++++++++++++++++++++++++++++++++++++++++
arch/mips/kernel/mcount.S | 47 ++++++++++++++++++++++-
3 files changed, 140 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 0be30cf..4cf11f5 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

@@ -74,3 +76,94 @@ int __init ftrace_dyn_arch_init(void *data)
return 0;
}
#endif /* CONFIG_DYNAMIC_FTRACE */
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+
+#define S_RA (0x2fbf << 16) /* 32bit: afbf, 64bit: ffbf */
+#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;
+
+ /* get the code at "ip" */
+ code = *(unsigned int *)ip;
+
+ /* If we hit the "move s8(fp), sp" instruction before finding
+ * where the ra is stored, then this is a leaf function and it
+ * does not store the ra on the stack. */
+ 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;
+
+ ftrace_graph_stop();
+ WARN_ON(1);
+ return parent_addr;
+}
+
+/*
+ * 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;
+ struct ftrace_graph_ent trace;
+ unsigned long return_hooker = (unsigned long)
+ &return_to_handler;
+
+ if (unlikely(atomic_read(&current->tracing_graph_pause)))
+ return;
+
+ /* "parent" is the stack address saved the return address of the caller
+ * of _mcount, for a leaf function not save the return address in the
+ * stack address, so, we "emulate" one in _mcount's stack space, and
+ * hijack it directly, but for a non-leaf function, it will save the
+ * return address to the its stack space, so, we can not hijack the
+ * "parent" directly, but need to find the real stack address,
+ * ftrace_get_parent_addr() does it!
+ */
+
+ old = *parent;
+
+ parent = (unsigned long *)ftrace_get_parent_addr(self_addr, old,
+ (unsigned long)parent,
+ fp);
+
+ *parent = return_hooker;
+
+ 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 389be7b..a9ba888 100644
--- a/arch/mips/kernel/mcount.S
+++ b/arch/mips/kernel/mcount.S
@@ -99,7 +99,15 @@ NESTED(_mcount, PT_SIZE, ra)
PTR_L t1, ftrace_trace_function /* Prepare t1 for (1) */
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

@@ -118,5 +126,42 @@ 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
--
1.6.2.1



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