On Tue, Apr 9, 2024, at 17:01, Ard Biesheuvel wrote: > From: Ard Biesheuvel <ardb@xxxxxxxxxx> > > kallsyms is a directory of all the symbols in the vmlinux binary, and so > creating it is 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, and instead, provide fallback > definitions in the linker script that are only emitted if an unsatisfied > reference exists. > > While at it, drop the FRV specific annotation that these symbols reside > in .rodata - FRV is long gone. > > Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> # Boot > Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > Link: https://lkml.kernel.org/r/20230504174320.3930345-1-ardb%40kernel.org > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
