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libbpf: Handle GCC noreturn-turned-volatile quirk
[ Upstream commit32022fd97e
] 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:351131b51c
("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>
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1 changed files with 24 additions and 9 deletions
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@ -1141,6 +1141,20 @@ static void btf_dump_emit_mods(struct btf_dump *d, struct id_stack *decl_stack)
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}
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}
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static void btf_dump_drop_mods(struct btf_dump *d, struct id_stack *decl_stack)
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{
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const struct btf_type *t;
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__u32 id;
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while (decl_stack->cnt) {
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id = decl_stack->ids[decl_stack->cnt - 1];
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t = btf__type_by_id(d->btf, id);
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if (!btf_is_mod(t))
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return;
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decl_stack->cnt--;
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}
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}
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static void btf_dump_emit_name(const struct btf_dump *d,
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const char *name, bool last_was_ptr)
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{
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@ -1239,14 +1253,7 @@ static void btf_dump_emit_type_chain(struct btf_dump *d,
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* a const/volatile modifier for array, so we are
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* going to silently skip them here.
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*/
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while (decls->cnt) {
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next_id = decls->ids[decls->cnt - 1];
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next_t = btf__type_by_id(d->btf, next_id);
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if (btf_is_mod(next_t))
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decls->cnt--;
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else
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break;
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}
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btf_dump_drop_mods(d, decls);
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if (decls->cnt == 0) {
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btf_dump_emit_name(d, fname, last_was_ptr);
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@ -1274,7 +1281,15 @@ static void btf_dump_emit_type_chain(struct btf_dump *d,
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__u16 vlen = btf_vlen(t);
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int i;
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btf_dump_emit_mods(d, decls);
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/*
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* GCC emits extra volatile qualifier for
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* __attribute__((noreturn)) function pointers. Clang
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* doesn't do it. It's a GCC quirk for backwards
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* compatibility with code written for GCC <2.5. So,
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* similarly to extra qualifiers for array, just drop
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* them, instead of handling them.
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*/
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btf_dump_drop_mods(d, decls);
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if (decls->cnt) {
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btf_dump_printf(d, " (");
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btf_dump_emit_type_chain(d, decls, fname, lvl);
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