linux-kernel - [PATCH bpf-next v2 4/6] libbpf: Initialize the bpf_seq

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Date:   Wed, 24 Mar 2021 03:22:09 +0100
From:   Florent Revest <revest@...omium.org>
To:     bpf@...r.kernel.org
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        yhs@...com, kpsingh@...nel.org, jackmanb@...omium.org,
        linux-kernel@...r.kernel.org, Florent Revest <revest@...omium.org>
Subject: [PATCH bpf-next v2 4/6] libbpf: Initialize the bpf_seq_printf parameters array field by field

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@...omium.org>
---
 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)
+#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)
+
 /*
  * 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")				    \
-		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;							    \
 	})
 
 #endif
-- 
2.31.0.291.g576ba9dcdaf-goog