Re: [PATCHSET 00/12] tracing/uprobes: Add support for more fetch methods

Masami Hiramatsu
2013-07-04T06:51:59Z

(2013/07/03 21:35), Namhyung Kim wrote:
> Hello,
>
> This patchset implements memory (address), stack[N], deference,
> bitfield and retval (it needs uretprobe tho) fetch methods for
> uprobes. It's based on the previous work [1] done by Hyeoncheol Lee.
>
> Now kprobes and uprobes have their own fetch_type_tables and, in turn,
> memory and stack access methods. Other fetch methods are shared.
>
> For the dereference method, I added a new argument to fetch functions.
> It's because for uprobes it needs to know whether the given address is
> a file offset or a virtual address in an user process. For instance,
> in case of fetching from a memory directly (like @offset) it should
> convert the address (offset) to a virtual address of the process, but
> if it's a dereferencing, the given address already has the virtual
> address.

Thanks Namhyung,
I agree that uprobe requires a special (file-relative) dereference
code. I'll look into the basic implementation after fixing current
dynamic-event related bugs. :)
(I see, this one should be updated to the latest tree, after
merge window is closed)

Thank you,

>
> To determine this in a fetch function, I passed a pointer to
> trace_uprobe for direct fetch, and passed NULL for dereference.
>
>
> [1] https://lkml.org/lkml/2012/11/14/84
>
> Simple example:
>
> # cat foo.c
> int glob = -1;
> char str[] = "hello uprobe.";
>
> struct foo {
> unsigned int unused: 2;
> unsigned int foo: 20;
> unsigned int bar: 10;
> } foo = {
> .foo = 5,
> };
>
> int main(int argc, char *argv[])
> {
> long local = 0x1234;
>
> return 127;
> }
>
> # gcc -o foo -g foo.c
>
> # objdump -d foo | grep -A9 -F ' '
> 00000000004004b0 :
> 4004b0: 55 push %rbp
> 4004b1: 48 89 e5 mov %rsp,%rbp
> 4004b4: 89 7d ec mov %edi,-0x14(%rbp)
> 4004b7: 48 89 75 e0 mov %rsi,-0x20(%rbp)
> 4004bb: 48 c7 45 f8 34 12 00 movq $0x1234,-0x8(%rbp)
> 4004c2: 00
> 4004c3: b8 7f 00 00 00 mov $0x7f,%eax
> 4004c8: 5d pop %rbp
> 4004c9: c3 retq
>
> # nm foo | grep -e glob$ -e str -e foo
> 00000000006008bc D foo
> 00000000006008a8 D glob
> 00000000006008ac D str
>
> # perf probe -x /home/namhyung/tmp/foo -a 'foo=main+0x13 glob=@0x8a8:s32 \
> > str=@0x8ac:string bit=@0x8bc:b10@2/32 argc=%di local=-0x8(%bp)'
> Added new event:
> probe_foo:foo (on 0x4c3 with glob=@0x8a8:s32 str=@0x8ac:string
> bit=@0x8bc:b10@2/32 argc=%di local=-0x8(%bp))
>
> You can now use it in all perf tools, such as:
>
> perf record -e probe_foo:foo -aR sleep 1
>
> # perf record -e probe_foo:foo ./foo
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.001 MB perf.data (~33 samples) ]
>
> # perf script | grep -v ^#
> foo 2008 [002 2199.867154: probe_foo:foo (4004c3)
> glob=4294967295 str="hello uprobe." bit=5 argc=1 local=1234
>
> Note that 4294967295 is 0xffffffff.
>
> Obviously, the perf tools also need to be improved. I'll work on that
> later.
>
> This patchset is based on the current tip/perf/core. I also put this
> on my 'uprobe/fetch-v1' branch in my tree:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git
>
>
> Any comments are welcome, thanks.
> Namhyung
>
>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
>
> Hyeoncheol Lee (2):
> tracing/kprobes: Move fetch functions to trace_kprobe.c
> tracing/kprobes: Add fetch{,_size} member into symbol and deref fetch
> method
>
> Namhyung Kim (10):
> tracing/kprobes: Make stack and memory fetch functions static
> tracing/kprobes: Factor out struct trace_probe
> tracing/uprobes: Convert to struct trace_probe
> tracing/kprobes: Move common functions to trace_probe.c
> tracing/kprobes: Remove duplicate set_print_fmt()
> tracing/uprobes: Fetch args before reserving a ring buffer
> tracing/uprobes: Fix a comment for uprobe registration syntax
> tracing/kprobes: Add priv argument to fetch functions
> tracing/uprobes: Add more fetch functions
> tracing/uprobes: Add support for full argument access methods
>
> kernel/trace/trace_kprobe.c | 529 ++++++++++++++++++++++----------------------
> kernel/trace/trace_probe.c | 451 ++++++++++++++++++-------------------
> kernel/trace/trace_probe.h | 154 ++++++++++++-
> kernel/trace/trace_uprobe.c | 429 ++++++++++++++++++++++++-----------
> 4 files changed, 926 insertions(+), 637 deletions(-)
>

--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com