From: Ard Biesheuvel <[email protected]>
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 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 <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Andrii Nakryiko <[email protected]>
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 | 28 ++++++++++++++++++
kernel/bpf/btf.c | 4 +--
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, 49 insertions(+), 33 deletions(-)
--
2.44.0.478.gd926399ef9-goog