netdev - [PATCH bpf] libbpf: Fix BTF-to-C conversion of noreturn function pointers

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Date:   Mon,  8 Jun 2020 17:20:52 +0200
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     bpf@...r.kernel.org, andriin@...com
Cc:     ast@...nel.org, daniel@...earbox.net, kafai@...com,
        songliubraving@...com, yhs@...com, john.fastabend@...il.com,
        kpsingh@...omium.org, netdev@...r.kernel.org,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: [PATCH bpf] libbpf: Fix BTF-to-C conversion of noreturn function pointers

When trying to convert the BTF for a function pointer marked "noreturn"
to C code, bpftool currently generates a syntax error. This happens with
the exit() pointer in drivers/firmware/efi/libstub/efistub.h, in an
arm64 vmlinux. When dealing with this declaration:

	efi_status_t __noreturn (__efiapi *exit)(...);

bpftool produces the following output:

	efi_status_tvolatile  (*exit)(...);

Fix the error by inserting the space before the function modifier.

Fixes: 351131b51c7a ("libbpf: add btf_dump API for BTF-to-C conversion")
Signed-off-by: Jean-Philippe Brucker <jean-philippe@...aro.org>
---
 tools/lib/bpf/btf_dump.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 0c28ee82834b7..003f305fc2342 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -1111,9 +1111,11 @@ static void btf_dump_emit_type_decl(struct btf_dump *d, __u32 id,
 	d->decl_stack_cnt = stack_start;
 }
 
-static void btf_dump_emit_mods(struct btf_dump *d, struct id_stack *decl_stack)
+static void btf__dump_emit_mods(struct btf_dump *d, struct id_stack *decl_stack,
+				const char *prefix, const char *suffix)
 {
 	const struct btf_type *t;
+	const char *mod;
 	__u32 id;
 
 	while (decl_stack->cnt) {
@@ -1122,21 +1124,27 @@ static void btf_dump_emit_mods(struct btf_dump *d, struct id_stack *decl_stack)
 
 		switch (btf_kind(t)) {
 		case BTF_KIND_VOLATILE:
-			btf_dump_printf(d, "volatile ");
+			mod = "volatile";
 			break;
 		case BTF_KIND_CONST:
-			btf_dump_printf(d, "const ");
+			mod = "const";
 			break;
 		case BTF_KIND_RESTRICT:
-			btf_dump_printf(d, "restrict ");
+			mod = "restrict";
 			break;
 		default:
 			return;
 		}
+		btf_dump_printf(d, "%s%s%s", prefix, mod, suffix);
 		decl_stack->cnt--;
 	}
 }
 
+static void btf_dump_emit_mods(struct btf_dump *d, struct id_stack *decl_stack)
+{
+	btf__dump_emit_mods(d, decl_stack, "", " ");
+}
+
 static void btf_dump_emit_name(const struct btf_dump *d,
 			       const char *name, bool last_was_ptr)
 {
@@ -1270,7 +1278,7 @@ static void btf_dump_emit_type_chain(struct btf_dump *d,
 			__u16 vlen = btf_vlen(t);
 			int i;
 
-			btf_dump_emit_mods(d, decls);
+			btf__dump_emit_mods(d, decls, " ", "");
 			if (decls->cnt) {
 				btf_dump_printf(d, " (");
 				btf_dump_emit_type_chain(d, decls, fname, lvl);
-- 
2.27.0