linux-kernel - Re: [RFC PATCH v8 46/49] perf tools: Add prologue for BPF programs for fetching arguments

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Date:	Fri, 26 Jun 2015 12:23:43 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	<acme@...nel.org>, <ast@...mgrid.com>, <brendan.d.gregg@...il.com>,
	<daniel@...earbox.net>, <namhyung@...nel.org>,
	<masami.hiramatsu.pt@...achi.com>, <paulus@...ba.org>,
	<a.p.zijlstra@...llo.nl>, <mingo@...hat.com>, <jolsa@...nel.org>,
	<dsahern@...il.com>
CC:	<linux-kernel@...r.kernel.org>, <lizefan@...wei.com>,
	<hekuang@...wei.com>, <xiakaixu@...wei.com>, <pi3orama@....com>
Subject: Re: [RFC PATCH v8 46/49] perf tools: Add prologue for BPF programs
 for fetching arguments



On 2015/6/24 20:31, Wang Nan wrote:

[SNIP]

> diff --git a/tools/perf/util/bpf-prologue.h b/tools/perf/util/bpf-prologue.h
> new file mode 100644
> index 0000000..3f77606
> --- /dev/null
> +++ b/tools/perf/util/bpf-prologue.h
> @@ -0,0 +1,19 @@
> +/*
> + * Copyright (C) 2015, He Kuang <hekuang@...wei.com>
> + * Copyright (C) 2015, Huawei Inc.
> + */
> +#ifndef __BPF_PROLOGUE_H
> +#define __BPF_PROLOGUE_H
> +
> +#include <linux/filter.h>
> +#include "probe-event.h"
> +
> +#define BPF_PROLOGUE_MAX_ARGS 3
> +#define BPF_PROLOGUE_START_ARG_REG BPF_REG_3
> +#define BPF_PROLOGUE_FETCH_RESULT_REG BPF_REG_2
> +
> +int bpf__gen_prologue(struct probe_trace_arg *args, int nargs,
> +		      struct bpf_insn *new_prog, size_t *new_cnt,
> +		      size_t cnt_space);
> +

Here is a problem: if CONFIG_BPF_PROLOGUE is not set, a missing symbol
problem will be triggered.

I have updated this part in my patchset:

+/*
+ * Copyright (C) 2015, He Kuang <hekuang@...wei.com>
+ * Copyright (C) 2015, Huawei Inc.
+ */
+#ifndef __BPF_PROLOGUE_H
+#define __BPF_PROLOGUE_H
+
+#include <linux/compiler.h>
+#include <linux/filter.h>
+#include "probe-event.h"
+
+#define BPF_PROLOGUE_MAX_ARGS 3
+#define BPF_PROLOGUE_START_ARG_REG BPF_REG_3
+#define BPF_PROLOGUE_FETCH_RESULT_REG BPF_REG_2
+
+#ifdef HAVE_BPF_PROLOGUE
+int bpf__gen_prologue(struct probe_trace_arg *args, int nargs,
+                     struct bpf_insn *new_prog, size_t *new_cnt,
+                     size_t cnt_space);
+#else
+static inline int
+bpf__gen_prologue(struct probe_trace_arg *args __maybe_unused,
+                 int nargs __maybe_unused,
+                 struct bpf_insn *new_prog __maybe_unused,
+                 size_t *new_cnt,
+                 size_t cnt_space __maybe_unused)
+{
+       if (!new_cnt)
+               return -EINVAL;
+       *new_cnt = 0;
+       return 0;
+}
+#endif
+#endif /* __BPF_PROLOGUE_H */

> +#endif /* __BPF_PROLOGUE_H */


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