Re: [PATCH] xen/riscv: fix build issue for bullseye-riscv64 container

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 31/07/2024 4:07 pm, Oleksii Kurochko wrote:
> Address compilation error on bullseye-riscv64 container:
>    undefined reference to `guest_physmap_remove_page`
>
> Since there is no current implementation of `guest_physmap_remove_page()`,
> a stub function has been added.
>
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
> Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Usually we do Fixes/Reported-by tags first.  (We try to do tags in
chronological/logical order).

I've confirmed this fixes the issue, so Acked-by: Andrew Cooper
<andrew.cooper3@xxxxxxxxxx>

Having tried a different approach,

user@3c393ef3b4c0:/build/xen$ make
  UPD     include/xen/compile.h
Xen 4.20-unstable
make[1]: Nothing to be done for 'include'.
make[1]: 'arch/riscv/include/asm/asm-offsets.h' is up to date.
  CC      common/version.o
  LD      common/built_in.o
  CC      arch/riscv/setup.o
  LD      arch/riscv/built_in.o
  LD      prelink.o
  LDS     arch/riscv/xen.lds
riscv64-linux-gnu-ld      -T arch/riscv/xen.lds -N prelink.o \
    ./common/symbols-dummy.o -o ./.xen-syms.0
riscv64-linux-gnu-ld: prelink.o: in function `register_keyhandler':
/build/xen/common/keyhandler.c:106: undefined reference to
`guest_physmap_remove_page'
riscv64-linux-gnu-ld: ./.xen-syms.0: hidden symbol
`guest_physmap_remove_page' isn't defined
riscv64-linux-gnu-ld: final link failed: bad value
make[2]: *** [arch/riscv/Makefile:15: xen-syms] Error 1
make[1]: *** [build.mk:90: xen] Error 2
make: *** [Makefile:610: xen] Error 2
user@3c393ef3b4c0:/build/xen$ find . -name \*.o | while read F; do nm $F
| grep guest_physmap_remove_page && echo $F; done
                 U guest_physmap_remove_page
./common/memory.o
                 U guest_physmap_remove_page
./common/built_in.o
                 U guest_physmap_remove_page
./prelink.o


despite the linker fingering keyhandler.c (very likely a toolchain bug),
it's memory.o which has the undefined reference.

Looking at memory.i, there are calls in guest_remove_page(),
memory_exchange(), and do_memory_op(), and no obvious way to DCE any of
them.

However, with bookworm, while memory.i does still have the same calls,
the resulting object file has no undefined references, so clearly
something has DCE'd them.


Looking at both memory.o's, bookwork really does have no reference,
while bullseye's reference is in memory_exchange().

So I guess there is something complicated there which bookworm can DCE
but bullseye can't.

Either way, this is the right fix, so lets not worry any more.

~Andrew