Instead of being a thin wrapper which calls into bpf_trace_printk,
libbpf's bpf_printk convenience macro now chooses between
bpf_trace_printk and bpf_trace_vprintk. If the arg count (excluding
format string) is >3, use bpf_trace_vprintk, otherwise use the older
helper.
The motivation behind this added complexity - instead of migrating
entirely to bpf_trace_vprintk - is to maintain good developer experience
for users compiling against new libbpf but running on older kernels.
Users who are passing <=3 args to bpf_printk will see no change in their
bytecode.
__bpf_vprintk functions similarly to BPF_SEQ_PRINTF and BPF_SNPRINTF
macros elsewhere in the file - it allows use of bpf_trace_vprintk
without manual conversion of varargs to u64 array. Previous
implementation of bpf_printk macro is moved to __bpf_printk for use by
the new implementation.
This does change behavior of bpf_printk calls with >3 args in the "new
libbpf, old kernels" scenario. Before this patch, attempting to use 4
args to bpf_printk results in a compile-time error. After this patch,
using bpf_printk with 4 args results in a trace_vprintk helper call
being emitted and a load-time failure on older kernels.
Signed-off-by: Dave Marchevsky <davemarchevsky@xxxxxx>
---
tools/lib/bpf/bpf_helpers.h | 45 ++++++++++++++++++++++++++++++-------
1 file changed, 37 insertions(+), 8 deletions(-)
diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index b9987c3efa3c..5f087306cdfe 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -14,14 +14,6 @@
#define __type(name, val) typeof(val) *name
#define __array(name, val) typeof(val) *name[]
-/* Helper macro to print out debug messages */
-#define bpf_printk(fmt, ...) \
-({ \
- char ____fmt[] = fmt; \
- bpf_trace_printk(____fmt, sizeof(____fmt), \
- ##__VA_ARGS__); \
-})
-
/*
* Helper macro to place programs, maps, license in
* different sections in elf_bpf file. Section names
@@ -224,4 +216,41 @@ enum libbpf_tristate {
___param, sizeof(___param)); \
})
+/* Helper macro to print out debug messages */
+#define __bpf_printk(fmt, ...) \
+({ \
+ char ____fmt[] = fmt; \
+ bpf_trace_printk(____fmt, sizeof(____fmt), \
+ ##__VA_ARGS__); \
+})
+
+/*
+ * __bpf_vprintk wraps the bpf_trace_vprintk helper with variadic arguments
+ * instead of an array of u64.
+ */
+#define __bpf_vprintk(fmt, args...) \
+({ \
+ static const char ___fmt[] = fmt; \
+ unsigned long long ___param[___bpf_narg(args)]; \
+ \
+ _Pragma("GCC diagnostic push") \
+ _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \
+ ___bpf_fill(___param, args); \
+ _Pragma("GCC diagnostic pop") \
+ \
+ bpf_trace_vprintk(___fmt, sizeof(___fmt), \
+ ___param, sizeof(___param)); \
+})
+
+#define ___bpf_pick_printk(...) \
+ ___bpf_nth(_, ##__VA_ARGS__, __bpf_vprintk, __bpf_vprintk, __bpf_vprintk, \
+ __bpf_vprintk, __bpf_vprintk, __bpf_vprintk, __bpf_vprintk, \
+ __bpf_vprintk, __bpf_vprintk, __bpf_printk, __bpf_printk, \
+ __bpf_printk, __bpf_printk)
+
+#define bpf_printk(fmt, args...) \
+({ \
+ ___bpf_pick_printk(args)(fmt, args); \
+})
+
#endif
--
2.30.2
