Em Sun, Mar 07, 2021 at 10:44:21AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Sun, Mar 07, 2021 at 10:16:31AM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Sat, Mar 06, 2021 at 07:16:08PM -0800, Andrii Nakryiko escreveu:
> > > On Fri, Mar 5, 2021 at 6:22 PM Ilya Leoshkevich <iii@xxxxxxxxxxxxx> wrote:
> > > >
> > > > Some BPF programs compiled on s390 fail to load, because s390
> > > > arch-specific linux headers contain float and double types.
> > > >
> > > > Fix as follows:
> > > >
> > > > - Make DWARF loader fill base_type.float_type.
> > > >
> > > > - libbpf introduced support for the floating-point types in commit
> > > > 986962fade5, so update the libbpf submodule to that version and use
> > > > the new btf__add_float() function in order to emit the floating-point
> > > > types when base_type.float_type is set.
> > > >
> > > > Example of the resulting entry in the vmlinux BTF:
> > > >
> > > > [7164] FLOAT 'double' size=8
>
> > > [PATCH dwarves] would make it a bit clearer that this is pahole patch.
>
> > > But LGTM.
>
> > So older versions of bpftool will fail with a .BTF section having this
> > new float? I thought it would just skip it emitting a warning? Probably
> > not possible as we don't have the record size encoded in a header,
> > right?
>
> > [acme@five pahole]$ bpftool btf dump file vmlinux | grep -w FLOAT
> > [acme@five pahole]$ type pahole
> > pahole is /home/acme/bin/pahole
> > [acme@five pahole]$ ls -la ~/bin/pahole
> > lrwxrwxrwx. 1 acme acme 34 Jan 29 11:00 /home/acme/bin/pahole -> /home/acme/git/pahole/build/pahole
> > [acme@five pahole]$ pahole -J vmlinux
> > [acme@five pahole]$ bpftool btf dump file vmlinux | grep -w FLOAT | head
> > Error: failed to load BTF from vmlinux: Invalid argument
> > [acme@five pahole]$
> >
> > Perhaps the warning emitted by bpftool should suggest updating the tool
> > as it found a record type it doesn't know about?
> >
> > /me goes to update bpftool...
>
> Works with the bpftool in bpf-next:
>
> [acme@five pahole]$ bpftool btf dump file vmlinux | grep -w FLOAT | head
> [8006] FLOAT 'double' size=8
> [acme@five pahole]$
Applied, with this committer notes:
Committer testing:
$ rm -rf build # To update the libbpf git submodule
$ mkdir build
$ cd build
$ cmake ..
$ cd ..
$ make -C build
# No BTF_KIND_FLOAT before:
$ bpftool btf dump file vmlinux | grep -w FLOAT
$ type pahole
pahole is /home/acme/bin/pahole
$ ls -la ~/bin/pahole
lrwxrwxrwx. 1 acme acme 34 Jan 29 11:00 /home/acme/bin/pahole -> /home/acme/git/pahole/build/pahole
# Encode BTF:
$ pahole -J vmlinux
$ bpftool btf dump file vmlinux | grep -w FLOAT | head
Error: failed to load BTF from vmlinux: Invalid argument
$
# Update bpftool to what is in bpf-next, then try again:
$ bpftool btf dump file vmlinux | grep -w FLOAT
[8006] FLOAT 'double' size=8
$
# Now check that pahole works well, i.e. that the BTF loader works
$ pahole -F btf vmlinux -C sk_buff_head
struct sk_buff_head {
struct sk_buff * next; /* 0 8 */
struct sk_buff * prev; /* 8 8 */
__u32 qlen; /* 16 4 */
spinlock_t lock; /* 20 4 */
/* size: 24, cachelines: 1, members: 4 */
/* last cacheline: 24 bytes */
};
$
$ pahole -F btf vmlinux | wc -l
122676
$
Now will build a kernel with this new version, reboot, then push
publicly.
- Arnaldo
