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SubjectRe: [PATCHSET 00/13] tracing/uprobes: Add support for more fetch methods (v6)
(2013/10/29 15:53), 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.
>
> To determine this in a fetch function, I passed a pointer to
> trace_uprobe for direct fetch, and passed NULL for dereference.
>
> The patch 1-2 are bug fixes and can be applied independently.

You'd better add [BUGFIX] and send those separately. ;)
But anyway, I'm OK to pull those first two (and others too).


> Please look at patch 10 that uses per-cpu buffer for accessing user
> memory as suggested by Steven. While I tried hard not to mess things
> up there might be a chance I did something horrible. It'd be great if
> you guys take a look and give comments.
>
>
> * v6 changes:
> - add more Ack's from Masami
> - fix ref count of uprobe_cpu_buffer (thanks to Jovi)
>
> * v5 changes:
> - use user_stack_pointer() instead of GET_USP()
> - fix a bug in 'stack' fetch method of uprobes
>
> * v4 changes:
> - add Ack's from Masami
> - rearrange patches to make it easy for simple fixes to be applied
> - update documentation
> - use per-cpu buffer for storing args (thanks to Steve!)
>
>
> [1] https://lkml.org/lkml/2012/11/14/84
>
> A 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 '<main>'
> 00000000004004b0 <main>:
> 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=-1 str="hello uprobe." bit=5 argc=1 local=1234

Nice ! :)

Thank you,

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




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