Re: linux-next failing build due to missing cubictcp_state symbol

[Jiri Slaby]

On 03. 05. 21, 8:11, Jiri Slaby wrote:
> > > > > > 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:
> > #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}, {
> ...
> >     name = 0x7ffff68e0808 ".stream_open", addr = 65824, size = 72, 
> > sh_addr = 65536, generated = false}, {
> ...
> >     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.

regards,
--
js