On Thu, 27 Jul 2023 09:38:14 +0900
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> wrote:
> > Yep, BPF generation is more selective about what it emits in 1.25 to
> > avoid cases where a kernel function signature is ambiguous (multiple
> > functions of the same name with different signatures) or where it has
> > unexpected register use. You can observe this via pahole's --verbose
> > option (a lot of outut is emitted):
> >
> > In a built kernel directory (where unstripped vmlinux is present):
> > $ PAHOLE_FLAGS=$(./scripts/pahole_flags)
> > $ PAHOLE=/usr/local/bin/pahole
> > $ pahole --verbose -J $PAHOLE_FLAGS vmlinux > /tmp/pahole.out
>
> So this will generate BTF from vmlinux DWARF info.
>
> > If you want to investigate why a function has been left out, look for
> > "skipping" verbose output like this:
> >
> > skipping addition of 'access_error'(access_error) due to multiple
> > inconsistent function prototypes
> > skipping addition of
> > 'acpi_ex_convert_to_object_type_string'(acpi_ex_convert_to_object_type_string.isra.0)
> > due to unexpected register used for parameter
>
> Ah, that's nice. Let me try.
$ pahole --version
v1.23
$ pahole --verbose -J $PAHOLE_FLAGS vmlinux > /tmp/pahole.out
die__process: DW_TAG_compile_unit, DW_TAG_type_unit, DW_TAG_partial_unit or DW_TAG_skeleton_unit expected got INVALID (0x0)!
OK, so something failed.
$ grep skipping /tmp/pahole.out | wc -l
0
Nothing to be skipped.
$ grep -w kfree /tmp/pahole.out | wc -l
0
$ grep -w vfs_read /tmp/pahole.out | wc -l
0
But both kfree and vfs_read are not found.
$ perf probe -k ./vmlinux -V kfree
Available variables at kfree
@<kfree+0>
(unknown_type) object
$ perf probe -k ./vmlinux -V vfs_read
Available variables at vfs_read
@<vfs_read+0>
char* buf
loff_t* pos
size_t count
struct file* file
However, perf probe can find both in the DWARF info.
Thank you,
--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
