On Sat, Apr 20, 2024 at 11:00 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > On Sat, 20 Apr 2024 at 15:56, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > > > On Sat, 20 Apr 2024 at 15:42, Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > > > > > On Sat, Apr 20, 2024 at 9:35 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > > > > > > > On Sat, 20 Apr 2024 at 14:32, Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > > > > > > > > > On Fri, Apr 19, 2024 at 4:57 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > > > > > > > > > > > On Tue, 16 Apr 2024 at 16:40, <patchwork-bot+netdevbpf@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > Hello: > > > > > > > > > > > > > > This series was applied to bpf/bpf-next.git (master) > > > > > > > by Daniel Borkmann <daniel@xxxxxxxxxxxxx>: > > > > > > > > > > > > > > On Mon, 15 Apr 2024 18:20:42 +0200 you wrote: > > > > > > > > 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. > > > > > > > > > > > > > > > > [...] > > > > > > > > > > > > > > Here is the summary with links: > > > > > > > - [v4,1/3] kallsyms: Avoid weak references for kallsyms symbols > > > > > > > (no matching commit) > > > > > > > - [v4,2/3] vmlinux: Avoid weak reference to notes section > > > > > > > (no matching commit) > > > > > > > - [v4,3/3] btf: Avoid weak external references > > > > > > > https://git.kernel.org/bpf/bpf-next/c/fc5eb4a84e4c > > > > > > > > > > > > > > > > > > > > > > > > > Thanks. > > > > > > > > > > > > Masahiro, could you pick up patches #1 and #2 please? > > > > > > > > > > > > > > > > > > > > > I do not like PROVIDE() because it potentially shifts > > > > > a build error (i.e. link error) into > > > > > a run-time error, which is usually more difficult to debug > > > > > than build error. > > > > > > > > > > If someone references the kallsyms_* symbols > > > > > when CONFIG_KALLSYMS=n, it is likely a mistake. > > > > > In general, it should be reported as a link error. > > > > > > > > > > > > > OK, so the PROVIDE() should be conditional on CONFIG_KALLSYM=y. I can fix that. > > > > > > > > > You may need to take care of the dependency > > > between CONFIG_KALLSYMS and CONFIG_VMCORE_INFO > > > because kernel/vmcore_info.c has references > > > to the kallsyms_* symbols. > > > > > > (I am still not a big fan of PROVIDE() though) > > > > > > > > > OK, how about we use weak definitions (as opposed to weak references) > > in kernel/kallsyms.c, which will get superseded by the actual ones in > > the second linker pass. > > > > The only difference is that we will use some space in the binary for > > the weak definitions that are never used in the final build. I am fine if that fixes the issue. "git grep __weak" shows a bunch of weak definitions. > Btw those references in kernel/vmcore_info.c are guarded by #ifdef > CONFIG_KALLSYMS=y too. Ah, OK. Then, this is not an issue. -- Best Regards Masahiro Yamada
