From: Ard Biesheuvel <ardb@xxxxxxxxxx> Weak external linkage is intended for cases where a symbol reference can remain unsatisfied in the final link. Taking the address of such a symbol should yield NULL if the reference was not satisfied. Given that ordinary RIP or PC relative references cannot produce NULL, some kind of indirection is always needed in such cases, and in position independent code, this results in a GOT entry. In ordinary code, it is arch specific but amounts to the same thing. While unavoidable in some cases, weak references are currently also used to declare symbols that are always defined in the final link, but not in the first linker pass. This means we end up with worse codegen for no good reason. So let's clean this up, by providing preliminary definitions that are only used as a fallback. Changes since v3: - drop unnecessary preliminary definitions for BTF start/stop - add Jiri's ack Changes since v2: - fix build issue in patch #3 reported by Jiri - add Arnd's acks Changes since v1: - update second occurrence of BTF start/end markers - drop NULL check of __start_BTF[] which is no longer meaningful - avoid the preliminary BTF symbols if CONFIG_DEBUG_INFO_BTF is not set - add Andrii's ack to patch #3 - patches #1 and #2 unchanged Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx> Cc: linux-arch@xxxxxxxxxxxxxxx Cc: linux-kbuild@xxxxxxxxxxxxxxx Cc: bpf@xxxxxxxxxxxxxxx Cc: Andrii Nakryiko <andrii@xxxxxxxxxx> Cc: Jiri Olsa <olsajiri@xxxxxxxxx> Ard Biesheuvel (3): kallsyms: Avoid weak references for kallsyms symbols vmlinux: Avoid weak reference to notes section btf: Avoid weak external references include/asm-generic/vmlinux.lds.h | 19 +++++++++++++ kernel/bpf/btf.c | 7 +++-- kernel/bpf/sysfs_btf.c | 6 ++-- kernel/kallsyms.c | 6 ---- kernel/kallsyms_internal.h | 30 ++++++++------------ kernel/ksysfs.c | 4 +-- lib/buildid.c | 4 +-- 7 files changed, 43 insertions(+), 33 deletions(-) -- 2.44.0.683.g7961c838ac-goog
