bpf: use bpf_core_enum_value_exists() for HAVE_SET_RETVAL

Avoid probing in the agent, and do the feature detection
straight from BPF.

Signed-off-by: Julian Wiedmann <jwi@isovalent.com>

Author: julianwiedmann

bpf/complexity-tests/61/bpf_sock/1.txt

@@ -1,4 +1,3 @@
--DHAVE_SET_RETVAL=1
 -DSKIP_DEBUG=1
 -DENABLE_IPV4=1
 -DENABLE_IPV6=1

bpf/complexity-tests/61/bpf_sock/2.txt

@@ -1,4 +1,3 @@
--DHAVE_SET_RETVAL=1
 -DSKIP_DEBUG=1
 -DENABLE_IPV4=1
 -DENABLE_IPV6=1

bpf/complexity-tests/netnext/bpf_sock/1.txt

@@ -1,4 +1,3 @@
--DHAVE_SET_RETVAL=1
 -DSKIP_DEBUG=1
 -DENABLE_IPV4=1
 -DENABLE_IPV6=1

bpf/complexity-tests/netnext/bpf_sock/2.txt

@@ -1,4 +1,3 @@
--DHAVE_SET_RETVAL=1
 -DSKIP_DEBUG=1
 -DENABLE_IPV4=1
 -DENABLE_IPV6=1

bpf/include/bpf/builtins.h

@@ -552,3 +552,6 @@ static __always_inline __nobuiltin("memmove") void memmove(void *d,
 {
 	return __bpf_memmove(d, s, len);
 }
+
+#define bpf_core_enum_value_exists(enum_type, enum_value) \
+	__builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, 0)

bpf/include/bpf/helpers.h

@@ -6,6 +6,7 @@
 #include <linux/bpf.h>
 
 #include "ctx/ctx.h"
+#include "builtins.h"
 #include "compiler.h"
 
 #ifndef BPF_FUNC
@@ -107,11 +108,10 @@ static int BPF_FUNC(set_retval, int retval);
 
 static inline int try_set_retval(int retval __maybe_unused)
 {
-#ifdef HAVE_SET_RETVAL
-	return set_retval(retval);
-#else
+	if (bpf_core_enum_value_exists(enum bpf_func_id, BPF_FUNC_set_retval))
+		return set_retval(retval);
+
 	return 0;
-#endif
 }
 
 static long BPF_FUNC(loop, __u32 nr_loops, void *callback_fn, void *callback_ctx, __u64 flags);

pkg/datapath/linux/probes/probes.go

@@ -700,9 +700,6 @@ func ExecuteHeaderProbes(logger *slog.Logger) *FeatureProbes {
 	}
 
 	progHelpers := []ProgramHelper{
-		// common probes
-		{ebpf.CGroupSock, asm.FnSetRetval},
-
 		// xdp related probes
 		{ebpf.XDP, asm.FnXdpGetBuffLen},
 		{ebpf.XDP, asm.FnXdpLoadBytes},
@@ -717,9 +714,7 @@ func ExecuteHeaderProbes(logger *slog.Logger) *FeatureProbes {
 
 // writeCommonHeader defines macross for bpf/include/bpf/features.h
 func writeCommonHeader(writer io.Writer, probes *FeatureProbes) error {
-	features := map[string]bool{
-		"HAVE_SET_RETVAL": probes.ProgramHelpers[ProgramHelper{ebpf.CGroupSock, asm.FnSetRetval}],
-	}
+	features := map[string]bool{}
 
 	return writeFeatureHeader(writer, features, true)
 }