Re: [PATCH v3 2/9] ARM: tlbflush: Make TLB flushes into static inlines

[Linus Walleij <linus.walleij@linaro.org>]

On Mon, Mar 11, 2024 at 11:28 PM Sami Tolvanen <samitolvanen@google.com> wrote:
> On Mon, Mar 11, 2024 at 3:17 PM Linus Walleij <linus.walleij@linaro.org> wrote:
> >
> >   LD      .tmp_vmlinux.kallsyms1
> > ld.lld: error: undefined symbol: __kcfi_typeid_v7wbi_flush_user_tlb_range
> > >>> referenced by arch/arm/mm/tlb-v7.o:(.text+0x0) in archive vmlinux.a
> >
> > ld.lld: error: undefined symbol: __kcfi_typeid_v7wbi_flush_kern_tlb_range
> > >>> referenced by tlb-v7.S:60 (/mnt/storage/linus/linux-integrator/build-vexpress/../arch/arm/mm/tlb-v7.S:60)
> > >>>               arch/arm/mm/tlb-v7.o:(.text+0x40) in archive vmlinux.a
> >
> > ld.lld: error: undefined symbol: __kcfi_typeid_v7wbi_tlb_fns
> > >>> referenced by arch/arm/mm/tlb-v7.o:(.init.text+0x0) in archive vmlinux.a
>
> Clang only emits __kcfi_typeid symbols for functions that are
> address-taken in C code. You need to add __ADDRESSABLE(function)
> references to a C file somewhere for functions that otherwise are not
> address-taken.

Hey it works. So for example if for these functions I also add:

diff --git a/arch/arm/mm/flush.c b/arch/arm/mm/flush.c
index d19d140a10c7..23eb0f9358cb 100644
--- a/arch/arm/mm/flush.c
+++ b/arch/arm/mm/flush.c
@@ -18,6 +18,11 @@

 #include "mm.h"

+void v7wbi_flush_user_tlb_range(unsigned long, unsigned long, struct
vm_area_struct *);
+void v7wbi_flush_kern_tlb_range(unsigned long, unsigned long);
+__ADDRESSABLE(v7wbi_flush_user_tlb_range);
+__ADDRESSABLE(v7wbi_flush_kern_tlb_range);

Then that works.

The problem is that I also have to define all these function signatures that
are never used in C and there are quite a few of them, if I start listing them
all and #ifdefining them for selected CPUs it's not going to be pretty.

It can be done and they can be in a cfi-defs.c file though.
And it's better than __nocfi.

The complexity comes from the fact that arm can boot a kernel
with support for several different CPU:s.

The different CPU management functions are put in a list of supported
processors by the linker, and then e.g. the tlb maintenance functions
are dereferenced directly from *list->tlb in setup_processor()
in arch/arm/kernel/setup.c.

Yours,
Linus Walleij