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

[Jean-Philippe Brucker]

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-phili...@linaro.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