path: root/scripts/recordmcount.pl
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authorWu Zhangjin <wuzhangjin@gmail.com>2009-11-20 20:34:32 +0800
committerRalf Baechle <ralf@linux-mips.org>2009-12-17 01:57:23 +0000
commit538f19526e40ce7a5a296fad6a3121409c890adc (patch)
treebbdf5a55a08dafaf2497a241703e944563241ddc /scripts/recordmcount.pl
parente6299d2677e600f6a0bf93bbb89f20d3de5252de (diff)
MIPS: Tracing: Add dynamic function tracer support
With dynamic function tracer, by default, _mcount is defined as an "empty" function, it returns directly without any more action . When enabling it in user-space, it will jump to a real tracing function(ftrace_caller), and do the real job for us. Differ from the static function tracer, dynamic function tracer provides two functions ftrace_make_call()/ftrace_make_nop() to enable/disable the tracing of some indicated kernel functions(set_ftrace_filter). In the -v4 version, the implementation of this support is basically the same as X86 version does: _mcount is implemented as an empty function and ftrace_caller is implemented as a real tracing function respectively. But in this version, to support module tracing with the help of -mlong-calls in arch/mips/Makefile: MODFLAGS += -mlong-calls. The stuff becomes a little more complex. We need to cope with two different type of calling to _mcount. For the kernel part, the calling to _mcount(result of "objdump -hdr vmlinux"). is like this: 108: 03e0082d move at,ra 10c: 0c000000 jal 0 <fpcsr_pending> 10c: R_MIPS_26 _mcount 10c: R_MIPS_NONE *ABS* 10c: R_MIPS_NONE *ABS* 110: 00020021 nop For the module with -mlong-calls, it looks like this: c: 3c030000 lui v1,0x0 c: R_MIPS_HI16 _mcount c: R_MIPS_NONE *ABS* c: R_MIPS_NONE *ABS* 10: 64630000 daddiu v1,v1,0 10: R_MIPS_LO16 _mcount 10: R_MIPS_NONE *ABS* 10: R_MIPS_NONE *ABS* 14: 03e0082d move at,ra 18: 0060f809 jalr v1 In the kernel version, there is only one "_mcount" string for every kernel function, so, we just need to match this one in mcount_regex of scripts/recordmcount.pl, but in the module version, we need to choose one of the two to match. Herein, I choose the first one with "R_MIPS_HI16 _mcount". and In the kernel verion, without module tracing support, we just need to replace "jal _mcount" by "jal ftrace_caller" to do real tracing, and filter the tracing of some kernel functions via replacing it by a nop instruction. but as we have described before, the instruction "jal ftrace_caller" only left 32bit length for the address of ftrace_caller, it will fail when calling from the module space. so, herein, we must replace something else. the basic idea is loading the address of ftrace_caller to v1 via changing these two instructions: lui v1,0x0 addiu v1,v1,0 If we want to enable the tracing, we need to replace the above instructions to: lui v1, HI_16BIT_ftrace_caller addiu v1, v1, LOW_16BIT_ftrace_caller If we want to stop the tracing of the indicated kernel functions, we just need to replace the "jalr v1" to a nop instruction. but we need to replace two instructions and encode the above two instructions oursevles. Is there a simpler solution? Yes! Here it is, in this version, we put _mcount and ftrace_caller together, which means the address of _mcount and ftrace_caller is the same: _mcount: ftrace_caller: j ftrace_stub nop ...(do real tracing here)... ftrace_stub: jr ra move ra, at By default, the kernel functions call _mcount, and then jump to ftrace_stub and return. and when we want to do real tracing, we just need to remove that "j ftrace_stub", and it will run through the two "nop" instructions and then do the real tracing job. what about filtering job? we just need to do this: lui v1, hi_16bit_of_mcount <--> b 1f (0x10000004) addiu v1, v1, low_16bit_of_mcount move at, ra jalr v1 nop 1f: (rec->ip + 12) In linux-mips64, there will be some local symbols, whose name are prefixed by $L, which need to be filtered. thanks goes to Steven for writing the mips64-specific function_regex. In a conclusion, with RISC, things becomes easier with such a "stupid" trick, RISC is something like K.I.S.S, and also, there are lots of "simple" tricks in the whole ftrace support, thanks goes to Steven and the other folks for providing such a wonderful tracing framework! Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com> Cc: Nicholas Mc Guire <der.herr@hofr.at> Cc: zhangfx@lemote.com Cc: Wu Zhangjin <wuzhangjin@gmail.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: linux-kernel@vger.kernel.org Cc: linux-mips@linux-mips.org Patchwork: http://patchwork.linux-mips.org/patch/675/ Acked-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Diffstat (limited to 'scripts/recordmcount.pl')
1 files changed, 52 insertions, 0 deletions
diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
index ab368e8a007d..92f09fe9639e 100755
--- a/scripts/recordmcount.pl
+++ b/scripts/recordmcount.pl
@@ -295,6 +295,58 @@ if ($arch eq "x86_64") {
$ld .= " -m elf64_sparc";
$cc .= " -m64";
$objcopy .= " -O elf64-sparc";
+} elsif ($arch eq "mips") {
+ # To enable module support, we need to enable the -mlong-calls option
+ # of gcc for module, after using this option, we can not get the real
+ # offset of the calling to _mcount, but the offset of the lui
+ # instruction or the addiu one. herein, we record the address of the
+ # first one, and then we can replace this instruction by a branch
+ # instruction to jump over the profiling function to filter the
+ # indicated functions, or swith back to the lui instruction to trace
+ # them, which means dynamic tracing.
+ #
+ # c: 3c030000 lui v1,0x0
+ # c: R_MIPS_HI16 _mcount
+ # c: R_MIPS_NONE *ABS*
+ # c: R_MIPS_NONE *ABS*
+ # 10: 64630000 daddiu v1,v1,0
+ # 10: R_MIPS_LO16 _mcount
+ # 10: R_MIPS_NONE *ABS*
+ # 10: R_MIPS_NONE *ABS*
+ # 14: 03e0082d move at,ra
+ # 18: 0060f809 jalr v1
+ #
+ # for the kernel:
+ #
+ # 10: 03e0082d move at,ra
+ # 14: 0c000000 jal 0 <loongson_halt>
+ # 14: R_MIPS_26 _mcount
+ # 14: R_MIPS_NONE *ABS*
+ # 14: R_MIPS_NONE *ABS*
+ # 18: 00020021 nop
+ if ($is_module eq "0") {
+ $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
+ } else {
+ $mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_HI16\\s+_mcount\$";
+ }
+ $objdump .= " -Melf-trad".$endian."mips ";
+ if ($endian eq "big") {
+ $endian = " -EB ";
+ $ld .= " -melf".$bits."btsmip";
+ } else {
+ $endian = " -EL ";
+ $ld .= " -melf".$bits."ltsmip";
+ }
+ $cc .= " -mno-abicalls -fno-pic -mabi=" . $bits . $endian;
+ $ld .= $endian;
+ if ($bits == 64) {
+ $function_regex =
+ "^([0-9a-fA-F]+)\\s+<(.|[^\$]L.*?|\$[^L].*?|[^\$][^L].*?)>:";
+ $type = ".dword";
+ }
} elsif ($arch eq "microblaze") {
# Microblaze calls '_mcount' instead of plain 'mcount'.
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";

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