On Sat, Mar 27, 2021 at 12:01 AM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Tue, Mar 23, 2021 at 7:23 PM Florent Revest <revest@xxxxxxxxxxxx> wrote:
> >
> > When initializing the __param array with a one liner, if all args are
> > const, the initial array value will be placed in the rodata section but
> > because libbpf does not support relocation in the rodata section, any
> > pointer in this array will stay NULL.
> >
> > Fixes: c09add2fbc5a ("tools/libbpf: Add bpf_iter support")
> > Signed-off-by: Florent Revest <revest@xxxxxxxxxxxx>
> > ---
> > tools/lib/bpf/bpf_tracing.h | 26 ++++++++++++++++++++++----
> > 1 file changed, 22 insertions(+), 4 deletions(-)
> >
> > diff --git a/tools/lib/bpf/bpf_tracing.h b/tools/lib/bpf/bpf_tracing.h
> > index f9ef37707888..d9a4c3f77ff4 100644
> > --- a/tools/lib/bpf/bpf_tracing.h
> > +++ b/tools/lib/bpf/bpf_tracing.h
> > @@ -413,6 +413,22 @@ typeof(name(0)) name(struct pt_regs *ctx) \
> > } \
> > static __always_inline typeof(name(0)) ____##name(struct pt_regs *ctx, ##args)
> >
> > +#define ___bpf_fill0(arr, p, x)
>
> can you please double-check that no-argument BPF_SEQ_PRINTF won't
> generate a warning about spurious ';'? Maybe it's better to have zero
> case as `do {} while(0);` ?
>
> > +#define ___bpf_fill1(arr, p, x) arr[p] = x
> > +#define ___bpf_fill2(arr, p, x, args...) arr[p] = x; ___bpf_fill1(arr, p + 1, args)
> > +#define ___bpf_fill3(arr, p, x, args...) arr[p] = x; ___bpf_fill2(arr, p + 1, args)
> > +#define ___bpf_fill4(arr, p, x, args...) arr[p] = x; ___bpf_fill3(arr, p + 1, args)
> > +#define ___bpf_fill5(arr, p, x, args...) arr[p] = x; ___bpf_fill4(arr, p + 1, args)
> > +#define ___bpf_fill6(arr, p, x, args...) arr[p] = x; ___bpf_fill5(arr, p + 1, args)
> > +#define ___bpf_fill7(arr, p, x, args...) arr[p] = x; ___bpf_fill6(arr, p + 1, args)
> > +#define ___bpf_fill8(arr, p, x, args...) arr[p] = x; ___bpf_fill7(arr, p + 1, args)
> > +#define ___bpf_fill9(arr, p, x, args...) arr[p] = x; ___bpf_fill8(arr, p + 1, args)
> > +#define ___bpf_fill10(arr, p, x, args...) arr[p] = x; ___bpf_fill9(arr, p + 1, args)
> > +#define ___bpf_fill11(arr, p, x, args...) arr[p] = x; ___bpf_fill10(arr, p + 1, args)
> > +#define ___bpf_fill12(arr, p, x, args...) arr[p] = x; ___bpf_fill11(arr, p + 1, args)
> > +#define ___bpf_fill(arr, args...) \
> > + ___bpf_apply(___bpf_fill, ___bpf_narg(args))(arr, 0, args)
>
> cool. this is regular enough to easily comprehend :)
>
> > +
> > /*
> > * BPF_SEQ_PRINTF to wrap bpf_seq_printf to-be-printed values
> > * in a structure.
> > @@ -421,12 +437,14 @@ static __always_inline typeof(name(0)) ____##name(struct pt_regs *ctx, ##args)
> > ({ \
> > _Pragma("GCC diagnostic push") \
> > _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \
> > + unsigned long long ___param[___bpf_narg(args)]; \
> > static const char ___fmt[] = fmt; \
> > - unsigned long long ___param[] = { args }; \
> > + int __ret; \
> > + ___bpf_fill(___param, args); \
> > _Pragma("GCC diagnostic pop") \
>
> Let's clean this up a little bit;
> 1. static const char ___fmt should be the very first
> 2. _Pragma scope should be minimal necessary, which includes only
> ___bpf_fill, right?
> 3. Empty line after int __ret; and let's keep three underscores for consistency.
>
>
> > - int ___ret = bpf_seq_printf(seq, ___fmt, sizeof(___fmt), \
> > - ___param, sizeof(___param)); \
> > - ___ret; \
> > + __ret = bpf_seq_printf(seq, ___fmt, sizeof(___fmt), \
> > + ___param, sizeof(___param)); \
> > + __ret; \
>
> but actually you don't need __ret at all, just bpf_seq_printf() here, right?
Agreed with everything and also the indentation comment in 5/6, thanks.
