Re: 'perf probe' and symbols from .text.<something>

On Tue, 23 Feb 2021 00:05:08 +0900
Masami Hiramatsu [off-list ref] wrote:

Hi Evgenii,

On Thu, 18 Feb 2021 20:09:17 +0300
Evgenii Shatokhin [off-list ref] wrote:

quoted

Hi,

It seems, 'perf probe' can only see functions from .text section in the 
kernel modules, but not from .text.unlikely or other .text.* sections.

For example, with kernel 5.11 and nf_conntrack.ko with debug info, 'perf 
probe' succeeds for nf_conntrack_attach() from .text and fails for 
nf_ct_resolve_clash() from .text.unlikely:

Thanks for reporting it!

quoted

------------
# perf probe -v -m nf_conntrack nf_ct_resolve_clash
probe-definition(0): nf_ct_resolve_clash
symbol:nf_ct_resolve_clash file:(null) line:0 offset:0 return:0 lazy:(null)
0 arguments
Failed to get build-id from nf_conntrack.
Cache open error: -1
Open Debuginfo file: 
/lib/modules/5.11.0-test01/kernel/net/netfilter/nf_conntrack.ko
Try to find probe point from debuginfo.
Matched function: nf_ct_resolve_clash [33616]
Probe point found: nf_ct_resolve_clash+0
Found 1 probe_trace_events.
Post processing failed or all events are skipped. (-2)
Probe point 'nf_ct_resolve_clash' not found.
   Error: Failed to add events. Reason: No such file or directory (Code: -2)

[...]

quoted

Is there a way to allow probing of functions in .text.<something> ?

BTW, just for putting a probe on nf_ct_resolve_clash, please give the module *path*
instead of the module *name*. For example,

perf probe -v -m /lib/modules/5.11.0-test01/kernel/net/netfilter/nf_conntrack.ko nf_ct_resolve_clash

This should work (at least works for me), because it directly loads the symbols from the .ko file.

Thank you,

-- 
Masami Hiramatsu [off-list ref]