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[PATCH -v6 12/13] tracing: add function graph tracer support for MIPS

To: linux-mips@linux-mips.org, linux-kernel@vger.kernel.org
Subject: [PATCH -v6 12/13] tracing: add function graph tracer support for MIPS
From: Wu Zhangjin <wuzhangjin@gmail.com>
Date: Mon, 26 Oct 2009 23:13:29 +0800
Cc: Wu Zhangjin <wuzhangjin@gmail.com>, Frederic Weisbecker <fweisbec@gmail.com>, rostedt@goodmis.org, Thomas Gleixner <tglx@linutronix.de>, Ralf Baechle <ralf@linux-mips.org>, Richard Sandiford <rdsandiford@googlemail.com>, Nicholas Mc Guire <der.herr@hofr.at>, David Daney <ddaney@caviumnetworks.com>, Adam Nemet <anemet@caviumnetworks.com>, Patrik Kluba <kpajko79@gmail.com>
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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.

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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