On Mon, May 03, 2021 at 12:08:02PM +0200, Jiri Olsa wrote:

On Mon, May 03, 2021 at 10:59:44AM +0200, Jiri Slaby wrote:

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CCing pahole people.

On 03. 05. 21, 9:59, Jiri Slaby wrote:

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On 03. 05. 21, 8:11, Jiri Slaby wrote:

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looks like vfs_truncate did not get into BTF data,
I'll try to reproduce

_None_ of the functions are generated by pahole -J from
debuginfo on ppc64. debuginfo appears to be correct. Neither
pahole -J fs/open.o works correctly. collect_functions in
dwarves seems to be defunct on ppc64... "functions" array is
bogus (so find_function -- the bsearch -- fails).

It's not that bogus. I forgot an asterisk:

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#0  find_function (btfe=0x100269f80, name=0x10024631c
"stream_open") at
/usr/src/debug/dwarves-1.21-1.1.ppc64/btf_encoder.c:350
(gdb) p (*functions)@84
$5 = {{name = 0x7ffff68e0922 ".__se_compat_sys_ftruncate", addr
= 75232, size = 72, sh_addr = 65536, generated = false}, {
    name = 0x7ffff68e019e ".__se_compat_sys_open", addr = 80592,
size = 216, sh_addr = 65536, generated = false}, {
    name = 0x7ffff68e0076 ".__se_compat_sys_openat", addr =
80816, size = 232, sh_addr = 65536, generated = false}, {
    name = 0x7ffff68e0908 ".__se_compat_sys_truncate", addr =
74304, size = 100, sh_addr = 65536, generated = false}, {

...

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    name = 0x7ffff68e0808 ".stream_open", addr = 65824, size =
72, sh_addr = 65536, generated = false}, {

...

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    name = 0x7ffff68e0751 ".vfs_truncate", addr = 73392, size =
544, sh_addr = 65536, generated = false}}

The dot makes the difference, of course. The question is why is it
there? I keep looking into it. Only if someone has an immediate
idea...

Well, .vfs_truncate is in .text (and contains an ._mcount call). And
vfs_truncate is in .opd (w/o an ._mcount call). Since setup_functions
excludes all functions without the ._mcount call, is_ftrace_func later
returns false for such functions and they are filtered before the BTF
processing.

Technically, get_vmlinux_addrs looks at a list of functions between
__start_mcount_loc and __stop_mcount_loc and considers only the listed.

I don't know what the correct fix is (exclude .opd functions from the
filter?). Neither why cross compiler doesn't fail, nor why ebi v2 avoids
this too.

Attaching a patch for pahole which fixes the issue, but I have no idea
whether it is the right fix at all.

hi,
we're considering to disable ftrace filter completely,
I guess that would solve this issue for ppc as well

  https://lore.kernel.org/bpf/20210501001653.x3b4rk4vk4iqv3n7@kafai-mbp.dhcp.thefacebook.com/ (local)

Just disabling the ftrace filter in pahole does not seem to fix it.

Is there some other place where it should be disabled?

Thanks

Michal