Em Mon, Mar 13, 2023 at 07:12:43PM +0200, Eduard Zingerman escreveu:
> On Mon, 2023-03-13 at 16:37 +0000, Alan Maguire wrote:
> [...]
> > sure; try adding "--skip_encoding_btf_inconsistent_proto --btf_gen_optimized".
> > I was testing with gcc 11.2.1.
>
> pahole -F dwarf \
> --flat_arrays \
> --sort --jobs \
> --suppress_aligned_attribute \
> --suppress_force_paddings \
> --suppress_packed \
> --lang_exclude rust \
> --show_private_classes \
> --skip_encoding_btf_inconsistent_proto \
> --btf_gen_optimized \
> ./vmlinux
>
> Like this, right?
> gcc 11.3, pahole master, still don't see this in function prototypes,
> maybe I have a simpler kernel config...
>
> [...]
>
> > > On the other hand, I see it in a few structure definitions, e.g. here
> > > is original C code (include/linux/sysrq.h:32):
> > >
> > > struct sysrq_key_op {
> > > void (* const handler)(int);
> > > const char * const help_msg;
> > > const char * const action_msg;
> > > const int enable_mask;
> > > };
> > >
> > > And here is how it is reconstructed from DWARF (same happens when
> > > reconstructed from BTF):
> > >
> > > struct sysrq_key_op {
> > > const void (*handler)(int); /* 0 8 */
> > > const const char * help_msg; /* 8 8 */
> > > const const char * action_msg; /* 16 8 */
> > > const int enable_mask; /* 24 4 */
> > >
> > > /* size: 32, cachelines: 1, members: 4 */
> > > /* padding: 4 */
> > > /* last cacheline: 32 bytes */
> > > };
> > >
> > > So it seems to be a general issue with modifiers printing.
> > >
> >
> > So it seems like the modifier ordering isn't preserved, even though
> > the final BTF representation looks right? Thanks!
>
> Yes, BTF looks right, bpftool prints the structure correctly.
Yes, the problem is in pahole's fprintf.c code
⬢[acme@toolbox pahole]$ cat const-pointer-const.c
#include <stdio.h>
struct foo {
const char * const s;
};
int main(int argc, const char *argv[])
{
struct foo bar = { .s = argv[1], };
return printf("%s: %s\n", argv[0], bar.s);
}
⬢[acme@toolbox pahole]$ gcc -g const-pointer-const.c -o const-pointer-const
⬢[acme@toolbox pahole]$ pahole const-pointer-const
struct foo {
const constchar * s; /* 0 8 */
/* size: 8, cachelines: 1, members: 1 */
/* last cacheline: 8 bytes */
};
⬢[acme@toolbox pahole]$
Seems a long standing bug, so if you fix the whitespace issue we can
progress and not let this problem prevent the release of 1.25, agreed?
- Arnaldo
