On Sat, Apr 20, 2024 at 11:53 PM Ard Biesheuvel <ardb+git@xxxxxxxxxx> wrote: > > From: Ard Biesheuvel <ardb@xxxxxxxxxx> > > kallsyms is a directory of all the symbols in the vmlinux binary, and so > creating it poses somewhat of a chicken-and-egg problem, as its non-zero > size affects the layout of the binary, and therefore the values of the > symbols. > > For this reason, the kernel is linked more than once, and the first pass > does not include any kallsyms data at all. For the linker to accept > this, the symbol declarations describing the kallsyms metadata are > emitted as having weak linkage, so they can remain unsatisfied. During > the subsequent passes, the weak references are satisfied by the kallsyms > metadata that was constructed based on information gathered from the > preceding passes. > > Weak references lead to somewhat worse codegen, because taking their > address may need to produce NULL (if the reference was unsatisfied), and > this is not usually supported by RIP or PC relative symbol references. > > Given that these references are ultimately always satisfied in the final > link, let's drop the weak annotation on the declarations, and instead, > provide fallback definitions with weak linkage. This informs the > compiler that ultimately, the reference will always be satisfied. > > While at it, drop the FRV specific annotation that these symbols reside > in .rodata - FRV is long gone. > > Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx> > Cc: linux-kbuild@xxxxxxxxxxxxxxx > Acked-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> > Acked-by: Arnd Bergmann <arnd@xxxxxxxx> > Link: https://lore.kernel.org/all/20240415075837.2349766-5-ardb+git@xxxxxxxxxx > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > --- > v5: - avoid PROVIDE() in the linker script, use weak definitions instead > - drop tested-by, replace reviewed-by with acked-by > Applied to linux-kbuild. Thanks. -- Best Regards Masahiro Yamada
