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?
> })
>
> #endif
> --
> 2.31.0.291.g576ba9dcdaf-goog
>
