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SubjectRe: [PATCH 1/1] libbpf: fix broken gcc pragma macros in bpf_helpers.h/bpf_tracing.h
On Mon, Jun 6, 2022 at 6:28 AM James Hilliard <james.hilliard1@gmail.com> wrote:
>
> It seems the gcc preprocessor breaks unless pragmas are wrapped
> individually inside macros.
>
> Fixes errors like:
> error: expected identifier or '(' before '#pragma'
> 106 | SEC("cgroup/bind6")
> | ^~~
>
> error: expected '=', ',', ';', 'asm' or '__attribute__' before '#pragma'
> 114 | char _license[] SEC("license") = "GPL";
> | ^~~
>

We've been using this macro in this form for a while with no errors.
How do you get these errors in the first place? _Pragma is supposed to
be a full equivalent of #pragma specifically to be able to be used in
macros, so these work-arounds shouldn't be necessary. Let's first try
to root cause this.

> Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
> ---
> tools/lib/bpf/bpf_helpers.h | 26 ++++++++++++++------------
> tools/lib/bpf/bpf_tracing.h | 26 ++++++++++++++------------
> 2 files changed, 28 insertions(+), 24 deletions(-)
>
> diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
> index fb04eaf367f1..6d159082727d 100644
> --- a/tools/lib/bpf/bpf_helpers.h
> +++ b/tools/lib/bpf/bpf_helpers.h
> @@ -22,11 +22,13 @@
> * To allow use of SEC() with externs (e.g., for extern .maps declarations),
> * make sure __attribute__((unused)) doesn't trigger compilation warning.
> */
> +#define __gcc_helpers_pragma(x) _Pragma(#x)
> +#define __gcc_helpers_diag_pragma(x) __gcc_helpers_pragma("GCC diagnostic " #x)
> #define SEC(name) \
> - _Pragma("GCC diagnostic push") \
> - _Pragma("GCC diagnostic ignored \"-Wignored-attributes\"") \
> + __gcc_helpers_diag_pragma(push) \
> + __gcc_helpers_diag_pragma(ignored "-Wignored-attributes") \
> __attribute__((section(name), used)) \
> - _Pragma("GCC diagnostic pop") \
> + __gcc_helpers_diag_pragma(pop)
>
> /* Avoid 'linux/stddef.h' definition of '__always_inline'. */
> #undef __always_inline
> @@ -215,10 +217,10 @@ enum libbpf_tristate {
> static const char ___fmt[] = fmt; \
> unsigned long long ___param[___bpf_narg(args)]; \
> \
> - _Pragma("GCC diagnostic push") \
> - _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \
> + __gcc_helpers_diag_pragma(push) \
> + __gcc_helpers_diag_pragma(ignored "-Wint-conversion") \
> ___bpf_fill(___param, args); \
> - _Pragma("GCC diagnostic pop") \
> + __gcc_helpers_diag_pragma(pop) \
> \
> bpf_seq_printf(seq, ___fmt, sizeof(___fmt), \
> ___param, sizeof(___param)); \
> @@ -233,10 +235,10 @@ enum libbpf_tristate {
> static const char ___fmt[] = fmt; \
> unsigned long long ___param[___bpf_narg(args)]; \
> \
> - _Pragma("GCC diagnostic push") \
> - _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \
> + __gcc_helpers_diag_pragma(push) \
> + __gcc_helpers_diag_pragma(ignored "-Wint-conversion") \
> ___bpf_fill(___param, args); \
> - _Pragma("GCC diagnostic pop") \
> + __gcc_helpers_diag_pragma(pop) \
> \
> bpf_snprintf(out, out_size, ___fmt, \
> ___param, sizeof(___param)); \
> @@ -264,10 +266,10 @@ enum libbpf_tristate {
> static const char ___fmt[] = fmt; \
> unsigned long long ___param[___bpf_narg(args)]; \
> \
> - _Pragma("GCC diagnostic push") \
> - _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \
> + __gcc_helpers_diag_pragma(push) \
> + __gcc_helpers_diag_pragma(ignored "-Wint-conversion") \
> ___bpf_fill(___param, args); \
> - _Pragma("GCC diagnostic pop") \
> + __gcc_helpers_diag_pragma(pop) \
> \
> bpf_trace_vprintk(___fmt, sizeof(___fmt), \
> ___param, sizeof(___param)); \
> diff --git a/tools/lib/bpf/bpf_tracing.h b/tools/lib/bpf/bpf_tracing.h
> index 01ce121c302d..e08ffc290b3e 100644
> --- a/tools/lib/bpf/bpf_tracing.h
> +++ b/tools/lib/bpf/bpf_tracing.h
> @@ -422,16 +422,18 @@ struct pt_regs;
> * This is useful when using BPF helpers that expect original context
> * as one of the parameters (e.g., for bpf_perf_event_output()).
> */
> +#define __gcc_tracing_pragma(x) _Pragma(#x)
> +#define __gcc_tracing_diag_pragma(x) __gcc_tracing_pragma("GCC diagnostic " #x)
> #define BPF_PROG(name, args...) \
> name(unsigned long long *ctx); \
> static __attribute__((always_inline)) typeof(name(0)) \
> ____##name(unsigned long long *ctx, ##args); \
> typeof(name(0)) name(unsigned long long *ctx) \
> { \
> - _Pragma("GCC diagnostic push") \
> - _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \
> + __gcc_tracing_diag_pragma(push) \
> + __gcc_tracing_diag_pragma(ignored "-Wint-conversion") \
> return ____##name(___bpf_ctx_cast(args)); \
> - _Pragma("GCC diagnostic pop") \
> + __gcc_tracing_diag_pragma(pop) \
> } \
> static __attribute__((always_inline)) typeof(name(0)) \
> ____##name(unsigned long long *ctx, ##args)
> @@ -462,10 +464,10 @@ static __attribute__((always_inline)) typeof(name(0)) \
> ____##name(struct pt_regs *ctx, ##args); \
> typeof(name(0)) name(struct pt_regs *ctx) \
> { \
> - _Pragma("GCC diagnostic push") \
> - _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \
> + __gcc_tracing_diag_pragma(push) \
> + __gcc_tracing_diag_pragma(ignored "-Wint-conversion") \
> return ____##name(___bpf_kprobe_args(args)); \
> - _Pragma("GCC diagnostic pop") \
> + __gcc_tracing_diag_pragma(pop) \
> } \
> static __attribute__((always_inline)) typeof(name(0)) \
> ____##name(struct pt_regs *ctx, ##args)
> @@ -486,10 +488,10 @@ static __attribute__((always_inline)) typeof(name(0)) \
> ____##name(struct pt_regs *ctx, ##args); \
> typeof(name(0)) name(struct pt_regs *ctx) \
> { \
> - _Pragma("GCC diagnostic push") \
> - _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \
> + __gcc_tracing_diag_pragma(push) \
> + __gcc_tracing_diag_pragma(ignored "-Wint-conversion") \
> return ____##name(___bpf_kretprobe_args(args)); \
> - _Pragma("GCC diagnostic pop") \
> + __gcc_tracing_diag_pragma(pop) \
> } \
> static __always_inline typeof(name(0)) ____##name(struct pt_regs *ctx, ##args)
>
> @@ -520,10 +522,10 @@ ____##name(struct pt_regs *ctx, ##args); \
> typeof(name(0)) name(struct pt_regs *ctx) \
> { \
> struct pt_regs *regs = PT_REGS_SYSCALL_REGS(ctx); \
> - _Pragma("GCC diagnostic push") \
> - _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \
> + __gcc_tracing_diag_pragma(push) \
> + __gcc_tracing_diag_pragma(ignored "-Wint-conversion") \
> return ____##name(___bpf_syscall_args(args)); \
> - _Pragma("GCC diagnostic pop") \
> + __gcc_tracing_diag_pragma(pop) \
> } \
> static __attribute__((always_inline)) typeof(name(0)) \
> ____##name(struct pt_regs *ctx, ##args)
> --
> 2.25.1
>

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