From: Andrii Nakryiko andriin@fb.com
[ Upstream commit 32022fd97ed34f6812802bf1288db27c313576f4 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- tools/lib/bpf/btf_dump.c | 33 ++++++++++++++++++++++++--------- 1 file changed, 24 insertions(+), 9 deletions(-)
diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c index 0c28ee82834b..653dbbe2e366 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);