libbpf: Turn btf_dedup_opts into OPTS-based struct

btf__dedup() and struct btf_dedup_opts were added before we figured out
OPTS mechanism. As such, btf_dedup_opts is non-extensible without
breaking an ABI and potentially crashing user application.

Unfortunately, btf__dedup() and btf_dedup_opts are short and succinct
names that would be great to preserve and use going forward. So we use
___libbpf_override() macro approach, used previously for bpf_prog_load()
API, to define a new btf__dedup() variant that accepts only struct btf *
and struct btf_dedup_opts * arguments, and rename the old btf__dedup()
implementation into btf__dedup_deprecated(). This keeps both source and
binary compatibility with old and new applications.

The biggest problem was struct btf_dedup_opts, which wasn't OPTS-based,
and as such doesn't have `size_t sz;` as a first field. But btf__dedup()
is a pretty rarely used API and I believe that the only currently known
users (besides selftests) are libbpf's own bpf_linker and pahole.
Neither use case actually uses options and just passes NULL. So instead
of doing extra hacks, just rewrite struct btf_dedup_opts into OPTS-based
one, move btf_ext argument into those opts (only bpf_linker needs to
dedup btf_ext, so it's not a typical thing to specify), and drop never
used `dont_resolve_fwds` option (it was never used anywhere, AFAIK, it
makes BTF dedup much less useful and efficient).

Just in case, for old implementation, btf__dedup_deprecated(), detect
non-NULL options and error out with helpful message, to help users
migrate, if there are any user playing with btf__dedup().

The last remaining piece is dedup_table_size, which is another
anachronism from very early days of BTF dedup. Since then it has been
reduced to the only valid value, 1, to request forced hash collisions.
This is only used during testing. So instead introduce a bool flag to
force collisions explicitly.

This patch also adapts selftests to new btf__dedup() and btf_dedup_opts
use to avoid selftests breakage.

  [0] Closes: https://github.com/libbpf/libbpf/issues/281

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211111053624.190580-4-andrii@kernel.org

1 files changed, 7 insertions, 39 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/btf.c b/tools/testing/selftests/bpf/prog_tests/btf.c
index ebd1aa4d09d6..1e8b36d74df2 100644
--- a/tools/testing/selftests/bpf/prog_tests/btf.c
+++ b/tools/testing/selftests/bpf/prog_tests/btf.c
@@ -6627,7 +6627,7 @@ struct btf_dedup_test {
 	struct btf_dedup_opts opts;
 };
 
-const struct btf_dedup_test dedup_tests[] = {
+static struct btf_dedup_test dedup_tests[] = {
 
 {
 	.descr = "dedup: unused strings filtering",
@@ -6647,9 +6647,6 @@ const struct btf_dedup_test dedup_tests[] = {
 		},
 		BTF_STR_SEC("\0int\0long"),
 	},
-	.opts = {
-		.dont_resolve_fwds = false,
-	},
 },
 {
 	.descr = "dedup: strings deduplication",
@@ -6672,9 +6669,6 @@ const struct btf_dedup_test dedup_tests[] = {
 		},
 		BTF_STR_SEC("\0int\0long int"),
 	},
-	.opts = {
-		.dont_resolve_fwds = false,
-	},
 },
 {
 	.descr = "dedup: struct example #1",
@@ -6755,9 +6749,6 @@ const struct btf_dedup_test dedup_tests[] = {
 		},
 		BTF_STR_SEC("\0a\0b\0c\0d\0int\0float\0next\0s"),
 	},
-	.opts = {
-		.dont_resolve_fwds = false,
-	},
 },
 {
 	.descr = "dedup: struct <-> fwd resolution w/ hash collision",
@@ -6800,8 +6791,7 @@ const struct btf_dedup_test dedup_tests[] = {
 		BTF_STR_SEC("\0s\0x"),
 	},
 	.opts = {
-		.dont_resolve_fwds = false,
-		.dedup_table_size = 1, /* force hash collisions */
+		.force_collisions = true, /* force hash collisions */
 	},
 },
 {
@@ -6847,8 +6837,7 @@ const struct btf_dedup_test dedup_tests[] = {
 		BTF_STR_SEC("\0s\0x"),
 	},
 	.opts = {
-		.dont_resolve_fwds = false,
-		.dedup_table_size = 1, /* force hash collisions */
+		.force_collisions = true, /* force hash collisions */
 	},
 },
 {
@@ -6911,9 +6900,6 @@ const struct btf_dedup_test dedup_tests[] = {
 		},
 		BTF_STR_SEC("\0A\0B\0C\0D\0E\0F\0G\0H\0I\0J\0K\0L\0M\0N\0O\0P\0Q"),
 	},
-	.opts = {
-		.dont_resolve_fwds = false,
-	},
 },
 {
 	.descr = "dedup: no int/float duplicates",
@@ -6965,9 +6951,6 @@ const struct btf_dedup_test dedup_tests[] = {
 		},
 		BTF_STR_SEC("\0int\0some other int\0float"),
 	},
-	.opts = {
-		.dont_resolve_fwds = false,
-	},
 },
 {
 	.descr = "dedup: enum fwd resolution",
@@ -7009,9 +6992,6 @@ const struct btf_dedup_test dedup_tests[] = {
 		},
 		BTF_STR_SEC("\0e1\0e1_val\0e2\0e2_val"),
 	},
-	.opts = {
-		.dont_resolve_fwds = false,
-	},
 },
 {
 	.descr = "dedup: datasec and vars pass-through",
@@ -7054,8 +7034,7 @@ const struct btf_dedup_test dedup_tests[] = {
 		BTF_STR_SEC("\0.bss\0t"),
 	},
 	.opts = {
-		.dont_resolve_fwds = false,
-		.dedup_table_size = 1
+		.force_collisions = true
 	},
 },
 {
@@ -7099,9 +7078,6 @@ const struct btf_dedup_test dedup_tests[] = {
 		},
 		BTF_STR_SEC("\0t\0a1\0a2\0f\0tag"),
 	},
-	.opts = {
-		.dont_resolve_fwds = false,
-	},
 },
 {
 	.descr = "dedup: func/func_param tags",
@@ -7152,9 +7128,6 @@ const struct btf_dedup_test dedup_tests[] = {
 		},
 		BTF_STR_SEC("\0a1\0a2\0f\0tag1\0tag2\0tag3"),
 	},
-	.opts = {
-		.dont_resolve_fwds = false,
-	},
 },
 {
 	.descr = "dedup: struct/struct_member tags",
@@ -7200,9 +7173,6 @@ const struct btf_dedup_test dedup_tests[] = {
 		},
 		BTF_STR_SEC("\0t\0m1\0m2\0tag1\0tag2\0tag3"),
 	},
-	.opts = {
-		.dont_resolve_fwds = false,
-	},
 },
 {
 	.descr = "dedup: typedef tags",
@@ -7233,9 +7203,6 @@ const struct btf_dedup_test dedup_tests[] = {
 		},
 		BTF_STR_SEC("\0t\0tag1\0tag2\0tag3"),
 	},
-	.opts = {
-		.dont_resolve_fwds = false,
-	},
 },
 
 };
@@ -7293,7 +7260,7 @@ static void dump_btf_strings(const char *strs, __u32 len)
 
 static void do_test_dedup(unsigned int test_num)
 {
-	const struct btf_dedup_test *test = &dedup_tests[test_num - 1];
+	struct btf_dedup_test *test = &dedup_tests[test_num - 1];
 	__u32 test_nr_types, expect_nr_types, test_btf_size, expect_btf_size;
 	const struct btf_header *test_hdr, *expect_hdr;
 	struct btf *test_btf = NULL, *expect_btf = NULL;
@@ -7337,7 +7304,8 @@ static void do_test_dedup(unsigned int test_num)
 		goto done;
 	}
 
-	err = btf__dedup(test_btf, NULL, &test->opts);
+	test->opts.sz = sizeof(test->opts);
+	err = btf__dedup(test_btf, &test->opts);
 	if (CHECK(err, "btf_dedup failed errno:%d", err)) {
 		err = -1;
 		goto done;