Re: [PATCH bpf-next v2 1/2] bpf: Unify data extension operation of jited_ksyms and jited_linfo

[Pu Lehui]

On 2022/5/7 4:52, John Fastabend wrote:
> Pu Lehui wrote:
> > We found that 32-bit environment can not print bpf line info due
> > to data inconsistency between jited_ksyms[0] and jited_linfo[0].
> >
> > For example:
> > jited_kyms[0] = 0xb800067c, jited_linfo[0] = 0xffffffffb800067c
> >
> > We know that both of them store bpf func address, but due to the
> > different data extension operations when extended to u64, they may
> > not be the same. We need to unify the data extension operations of
> > them.
> >
> > Signed-off-by: Pu Lehui <pulehui@xxxxxxxxxx>
> > ---
> >   kernel/bpf/syscall.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index e9e3e49c0eb7..18137ea5190d 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -3871,13 +3871,16 @@ static int bpf_prog_get_info_by_fd(struct file *file,
> >   		info.nr_jited_line_info = 0;
> >   	if (info.nr_jited_line_info && ulen) {
> >   		if (bpf_dump_raw_ok(file->f_cred)) {
> > +			unsigned long jited_linfo_addr;
> >   			__u64 __user *user_linfo;
> >   			u32 i;
> >   
> >   			user_linfo = u64_to_user_ptr(info.jited_line_info);
> >   			ulen = min_t(u32, info.nr_jited_line_info, ulen);
> >   			for (i = 0; i < ulen; i++) {
> > -				if (put_user((__u64)(long)prog->aux->jited_linfo[i],
> > +				jited_linfo_addr = (unsigned long)
> > +					prog->aux->jited_linfo[i];
> > +				if (put_user((__u64) jited_linfo_addr,
> >   					     &user_linfo[i]))
>
> the logic is fine but i'm going to nitpick a bit this 4 lines is ugly
> just make it slightly longer than 80chars or use a shoarter name? For
> example,
>
> 			for (i = 0; i < ulen; i++) {
> 				unsigned long l;
>
> 				l = (unsigned long) prog->aux->jited_linfo[i];
> 				if (put_user((__u64) l, &user_linfo[i]))
>
> is much nicer -- no reason to smash single assignment across multiple
> lines. My $.02.

Okay, It sounds good. I will make change in next version. Thanks.

> Thanks,
> John
> .