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authorAndrii Nakryiko <andriin@fb.com>2020-06-09 22:23:35 -0700
committerDaniel Borkmann <daniel@iogearbox.net>2020-06-10 13:37:02 +0200
commit32022fd97ed34f6812802bf1288db27c313576f4 (patch)
tree1afdc5598b61e41a8114a4fe5c733e3ae8cb6ae6
parent8ca8d4a841730c02e77bf3c87bf658cc44f364b9 (diff)
downloadlinux-32022fd97ed34f6812802bf1288db27c313576f4.tar.gz
libbpf: Handle GCC noreturn-turned-volatile quirk
Handle a GCC quirk of emitting extra volatile modifier in DWARF (and subsequently preserved in BTF by pahole) for function pointers marked as __attribute__((noreturn)). This was the way to mark such functions before GCC 2.5 added noreturn attribute. Drop such func_proto modifiers, similarly to how it's done for array (also to handle GCC quirk/bug). Such volatile attribute is emitted by GCC only, so existing selftests can't express such test. Simple repro is like this (compiled with GCC + BTF generated by pahole): struct my_struct { void __attribute__((noreturn)) (*fn)(int); }; struct my_struct a; Without this fix, output will be: struct my_struct { voidvolatile (*fn)(int); }; With the fix: struct my_struct { void (*fn)(int); }; Fixes: 351131b51c7a ("libbpf: add btf_dump API for BTF-to-C conversion") Reported-by: Jean-Philippe Brucker <jean-philippe@linaro.org> Signed-off-by: Andrii Nakryiko <andriin@fb.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Tested-by: Jean-Philippe Brucker <jean-philippe@linaro.org> Link: https://lore.kernel.org/bpf/20200610052335.2862559-1-andriin@fb.com
-rw-r--r--tools/lib/bpf/btf_dump.c33
1 files changed, 24 insertions, 9 deletions
diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index de07e55..bbb4303 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -1137,6 +1137,20 @@ static void btf_dump_emit_mods(struct btf_dump *d, struct id_stack *decl_stack)
}
}
+static void btf_dump_drop_mods(struct btf_dump *d, struct id_stack *decl_stack)
+{
+ const struct btf_type *t;
+ __u32 id;
+
+ while (decl_stack->cnt) {
+ id = decl_stack->ids[decl_stack->cnt - 1];
+ t = btf__type_by_id(d->btf, id);
+ if (!btf_is_mod(t))
+ return;
+ decl_stack->cnt--;
+ }
+}
+
static void btf_dump_emit_name(const struct btf_dump *d,
const char *name, bool last_was_ptr)
{
@@ -1235,14 +1249,7 @@ static void btf_dump_emit_type_chain(struct btf_dump *d,
* a const/volatile modifier for array, so we are
* going to silently skip them here.
*/
- while (decls->cnt) {
- next_id = decls->ids[decls->cnt - 1];
- next_t = btf__type_by_id(d->btf, next_id);
- if (btf_is_mod(next_t))
- decls->cnt--;
- else
- break;
- }
+ btf_dump_drop_mods(d, decls);
if (decls->cnt == 0) {
btf_dump_emit_name(d, fname, last_was_ptr);
@@ -1270,7 +1277,15 @@ static void btf_dump_emit_type_chain(struct btf_dump *d,
__u16 vlen = btf_vlen(t);
int i;
- btf_dump_emit_mods(d, decls);
+ /*
+ * GCC emits extra volatile qualifier for
+ * __attribute__((noreturn)) function pointers. Clang
+ * doesn't do it. It's a GCC quirk for backwards
+ * compatibility with code written for GCC <2.5. So,
+ * similarly to extra qualifiers for array, just drop
+ * them, instead of handling them.
+ */
+ btf_dump_drop_mods(d, decls);
if (decls->cnt) {
btf_dump_printf(d, " (");
btf_dump_emit_type_chain(d, decls, fname, lvl);