On Thu, May 18, 2023 at 9:17 AM Brian Hutchinson <b.hutch...@gmail.com> wrote:
>
> On Wed, May 17, 2023 at 12:08 PM Mathieu Desnoyers
> <mathieu.desnoy...@efficios.com> wrote:
> >
> > On 2023-05-16 22:11, Brian Hutchinson via lttng-dev wrote:
> > > Hi,
> > >
> > > I'm trying to figure out how to use uprobes with lttng.
> > >
> > > I can't use a normal uprobe for a line number just using the address I
> > > want to probe obtained from objdump? As in:
> > >
> > > echo 'p /usr/local/bin/my_app:0x2c3a8' >>
> > > /sys/kernel/debug/tracing/uprobe_events
> > >
> > > ... which isn't a function entry, it's just a line of code I want to
> > > probe on.
> > >
> > > This link says it has to be elf or sdt:
> > > https://lttng.org/man/1/lttng-enable-event/v2.11/#doc-opt--userspace-probe
> > >
> > > So can I not probe on just a line of code by specifying an address???
> > >
> > > It doesn't look like these methods above will do what I'm wanting to
> > > do. I've tried to find examples of using enable-event --kernel
> > > --userspace-probe= but there doesn't appear to be many.
> > >
> >
> > There are examples here:
> >
> > https://lttng.org/docs/v2.13/#doc-enabling-disabling-events
>
> I added a function that's called when the event I want to probe occurs.
>
> I tried to enable the event with:
> root@localhost:/usr/local/bin# lttng enable-event --kernel
> --userspace-probe=/usr/local/bin/my_app:my_probe_event
> Error: Missing event name(s).
>
> ... and:
>
> root@localhost:/usr/local/bin# lttng enable-event --kernel
> --userspace-probe=elf:/usr/local/bin/my_app:my_probe_event
> Error: Missing event name(s).
>
> I can do ${CROSS_COMPILE}objdump -d and verify that the symbol above
> for the function I added is indeed there.
>
> What am I doing wrong?
>
I updated my hello world to have a function I'd like to use the
--userspace-probe method on with the very original name of
'probe_function':
#include <stdio.h>
#include <lttng/tracef.h>
void probe_function(int i);
int main(int argc, char *argv[])
{
unsigned int i;
puts("Hello, World!\nPress Enter to continue...");
/*
* The following getchar() call only exists for the purpose of this
* demonstration, to pause the application in order for you to have
* time to list its tracepoints. You don't need it otherwise.
*/
getchar();
lttng_ust_tracef("Number %d, string %s", 23, "hi there!");
printf("Number %d, string %s", 23, "hi there!");
for (i = 0; i < argc; i++) {
lttng_ust_tracef("Number %d, argv %s", i, argv[i]);
printf("Number %d, argv %s", i, argv[i]);
}
puts("Quitting now!");
probe_function(i);
return 0;
}
void probe_function(int i) {
lttng_ust_tracef("Number %d, string %s", i * i, "i^2");
printf("Number %d, string %s", i * i, "i^2");
}
... and I get the same error as before when I try to enable the probe:
# lttng enable-event --kernel
--userspace-probe=/usr/local/bin/hello:probe_function
Error: Missing event name(s).
More system details below:
$ cat hello_objdump.txt
hello: file format elf64-littleaarch64
SYMBOL TABLE:
0000000000000238 l d .interp 0000000000000000 .interp
0000000000000254 l d .note.gnu.build-id 0000000000000000
.note.gnu.build-id
0000000000000278 l d .note.ABI-tag 0000000000000000
.note.ABI-tag
0000000000000298 l d .gnu.hash 0000000000000000 .gnu.hash
00000000000002b8 l d .dynsym 0000000000000000 .dynsym
00000000000004c8 l d .dynstr 0000000000000000 .dynstr
00000000000005ee l d .gnu.version 0000000000000000
.gnu.version
0000000000000620 l d .gnu.version_r 0000000000000000
.gnu.version_r
0000000000000660 l d .rela.dyn 0000000000000000 .rela.dyn
00000000000007b0 l d .rela.plt 0000000000000000 .rela.plt
0000000000000918 l d .init 0000000000000000 .init
0000000000000930 l d .plt 0000000000000000 .plt
0000000000000a40 l d .text 0000000000000000 .text
0000000000001194 l d .fini 0000000000000000 .fini
00000000000011a8 l d .rodata 0000000000000000 .rodata
00000000000013f0 l d .eh_frame_hdr 0000000000000000
.eh_frame_hdr
0000000000001468 l d .eh_frame 0000000000000000 .eh_frame
0000000000011d78 l d .init_array 0000000000000000
.init_array
0000000000011d88 l d .fini_array 0000000000000000
.fini_array
0000000000011d98 l d .dynamic 0000000000000000 .dynamic
0000000000011f98 l d .got 0000000000000000 .got
0000000000011fe8 l d .got.plt 0000000000000000 .got.plt
0000000000012078 l d .data 0000000000000000 .data
00000000000120d8 l d .bss 0000000000000000 .bss
0000000000000000 l d .comment 0000000000000000 .comment
0000000000000000 l d .debug_aranges 0000000000000000
.debug_aranges
0000000000000000 l d .debug_info 0000000000000000
.debug_info
0000000000000000 l d .debug_abbrev 0000000000000000
.debug_abbrev
0000000000000000 l d .debug_line 0000000000000000
.debug_line
0000000000000000 l d .debug_str 0000000000000000 .debug_str
0000000000000000 l d .debug_loc 0000000000000000 .debug_loc
0000000000000000 l d .debug_ranges 0000000000000000
.debug_ranges
0000000000000000 l df *ABS* 0000000000000000 abi-note.S
0000000000000000 l df *ABS* 0000000000000000 start.S
0000000000000000 l df *ABS* 0000000000000000 init.c
0000000000000000 l df *ABS* 0000000000000000 crti.S
0000000000000a78 l F .text 0000000000000014 call_weak_fn
0000000000000000 l df *ABS* 0000000000000000 crtn.S
0000000000000000 l df *ABS* 0000000000000000 crtstuff.c
0000000000000a90 l F .text 0000000000000000
deregister_tm_clones
0000000000000ac0 l F .text 0000000000000000 register_tm_clones
0000000000000b00 l F .text 0000000000000000
__do_global_dtors_aux
00000000000120d8 l O .bss 0000000000000001 completed.9125
0000000000011d88 l O .fini_array 0000000000000000
__do_global_dtors_aux_fini_array_entry
0000000000000b50 l F .text 0000000000000000 frame_dummy
0000000000011d78 l O .init_array 0000000000000000
__frame_dummy_init_array_entry
0000000000000000 l df *ABS* 0000000000000000 hello.c
0000000000000b54 l F .text 0000000000000120
lttng_ust_tracepoint__init_urcu_sym
0000000000000c74 l F .text 0000000000000028
lttng_ust_tracepoint_logging_debug_enabled
0000000000000c9c l F .text 000000000000007c
lttng_ust_tracepoints_print_disabled_message
00000000000013c0 l O .rodata 000000000000002d
__func__.5512
0000000000000d18 l F .text 00000000000000e8
lttng_ust__tracepoints__init
0000000000000e00 l F .text 0000000000000170
lttng_ust__tracepoints__destroy
0000000000000000 l df *ABS* 0000000000000000 elf-init.c
0000000000000000 l df *ABS* 0000000000000000 crtstuff.c
0000000000001610 l O .eh_frame 0000000000000000
__FRAME_END__
0000000000000000 l df *ABS* 0000000000000000
0000000000011d88 l .init_array 0000000000000000
__init_array_end
0000000000011d98 l O *ABS* 0000000000000000 _DYNAMIC
0000000000011d78 l .init_array 0000000000000000
__init_array_start
00000000000013f0 l .eh_frame_hdr 0000000000000000
__GNU_EH_FRAME_HDR
0000000000011f98 l O *ABS* 0000000000000000
_GLOBAL_OFFSET_TABLE_
0000000000000918 l F .init 0000000000000000 _init
0000000000001190 g F .text 0000000000000004 __libc_csu_fini
0000000000000000 w *UND* 0000000000000000
_ITM_deregisterTMCloneTable
0000000000012078 w .data 0000000000000000 data_start
00000000000120f0 w O .bss 0000000000000008 .hidden
lttng_ust_tracepoint_destructors_syms_ptr
00000000000120d8 g .bss 0000000000000000 __bss_start__
0000000000000000 w F *UND* 0000000000000000
__cxa_finalize@@GLIBC_2.17
0000000000000000 O *UND* 0000000000000000 stderr@@GLIBC_2.17
0000000000000000 F *UND* 0000000000000000
dlclose@@GLIBC_2.17
00000000000120f8 g .bss 0000000000000000 _bss_end__
00000000000120d8 g .data 0000000000000000 _edata
0000000000000000 F *UND* 0000000000000000 dlopen@@GLIBC_2.17
0000000000001194 g F .fini 0000000000000000 .hidden _fini
00000000000120f8 g .bss 0000000000000000 __bss_end__
0000000000000000 F *UND* 0000000000000000 getpid@@GLIBC_2.17
0000000000000000 F *UND* 0000000000000000 dlsym@@GLIBC_2.17
0000000000000000 F *UND* 0000000000000000
__libc_start_main@@GLIBC_2.17
0000000000000000 F *UND* 0000000000000000 memset@@GLIBC_2.17
00000000000120e8 w O .bss 0000000000000008 .hidden
lttng_ust_tracepoint_dlopen_ptr
0000000000012078 g .data 0000000000000000 __data_start
0000000000000000 w *UND* 0000000000000000 __gmon_start__
0000000000012080 g O .data 0000000000000000 .hidden
__dso_handle
00000000000120c0 w O .data 0000000000000018 .hidden
lttng_ust_tracepoint_destructors_syms
0000000000000000 F *UND* 0000000000000000 abort@@GLIBC_2.17
00000000000120e4 w O .bss 0000000000000004 .hidden
lttng_ust_tracepoint_ptrs_registered
00000000000011a8 g O .rodata 0000000000000004
_IO_stdin_used
0000000000012088 w O .data 0000000000000038 .hidden
lttng_ust_tracepoint_dlopen
0000000000000000 F *UND* 0000000000000000 puts@@GLIBC_2.17
00000000000120e0 w O .bss 0000000000000004 .hidden
lttng_ust_tracepoint_registered
0000000000001110 g F .text 000000000000007c __libc_csu_init
00000000000120f8 g .bss 0000000000000000 _end
0000000000000a40 g F .text 0000000000000000 _start
0000000000000000 F *UND* 0000000000000000
getchar@@GLIBC_2.17
00000000000120f8 g .bss 0000000000000000 __end__
00000000000120d8 g .bss 0000000000000000 __bss_start
0000000000000f70 g F .text 000000000000012c main
000000000000109c g F .text 0000000000000074 probe_function
0000000000000000 O *UND* 0000000000000000
lttng_ust_tracepoint_lttng_ust_tracef___event
00000000000120d8 g O .data 0000000000000000 .hidden
__TMC_END__
0000000000000000 w *UND* 0000000000000000
_ITM_registerTMCloneTable
0000000000000000 F *UND* 0000000000000000 printf@@GLIBC_2.17
0000000000000000 F *UND* 0000000000000000 getenv@@GLIBC_2.17
0000000000000000 F *UND* 0000000000000000
fprintf@@GLIBC_2.17
0000000000000000 F *UND* 0000000000000000 lttng_ust__tracef
# zcat /proc/config.gz | grep -i probe
CONFIG_GENERIC_IRQ_PROBE=y
CONFIG_ARCH_SUPPORTS_UPROBES=y
CONFIG_KPROBES=y
CONFIG_UPROBES=y
CONFIG_KRETPROBES=y
CONFIG_HAVE_KPROBES=y
CONFIG_HAVE_KRETPROBES=y
# CONFIG_TEST_ASYNC_DRIVER_PROBE is not set
CONFIG_GENERIC_CPU_AUTOPROBE=y
# CONFIG_MTD_JEDECPROBE is not set
CONFIG_TIMER_PROBE=y
CONFIG_KPROBE_EVENTS=y
# CONFIG_KPROBE_EVENTS_ON_NOTRACE is not set
CONFIG_UPROBE_EVENTS=y
CONFIG_PROBE_EVENTS=y
# CONFIG_KPROBE_EVENT_GEN_TEST is not set
# CONFIG_KPROBES_SANITY_TEST is not set
> >
> > Indeed inserting a lttng-modules uprobe within functions is not
> > supported at the moment, mainly because we prefer to err towards safety
> > and don't have the validation in place to prevent corrupting the
> > program's instructions if an end user would try to insert a uprobe at an
> > address which is not an instruction boundary.
> >
> > So we only support inserting uprobe on functions and SDT probes at
> > the moment.
> >
> > Thanks,
> >
> > Mathieu
> >
> >
> > > Thanks,
> > >
> > > Brian
> > > _______________________________________________
> > > lttng-dev mailing list
> > > lttng-dev@lists.lttng.org
> > > https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> >
> > --
> > Mathieu Desnoyers
> > EfficiOS Inc.
> > https://www.efficios.com
> >
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