Re: [PATCH] linux-user: Fix trivial build error on loongarch64

[WANG Xuerui <i.qemu@xen0n.name>]

On 2022/1/4 21:02, Philippe Mathieu-Daudé wrote:

> When building using GCC 8.3.0 on loongarch64 (Loongnix) we get:
>
>   In file included from ../linux-user/signal.c:33:
>   ../linux-user/host/loongarch64/host-signal.h: In function ‘host_signal_write’:
>   ../linux-user/host/loongarch64/host-signal.h:57:9: error: a label can only be part of a statement and a declaration is not a statement
>          uint32_t sel = (insn >> 15) & 0b11111111111;
>          ^~~~~~~~
>
> We don't use the 'sel' variable more than once, so drop it.
>
> Meson output for the record:
>
>   Host machine cpu family: loongarch64
>   Host machine cpu: loongarch64
>   C compiler for the host machine: cc (gcc 8.3.0 "cc (Loongnix 8.3.0-6.lnd.vec.27) 8.3.0")
>   C linker for the host machine: cc ld.bfd 2.31.1-system
So this issue indeed only happens on the Loongson-provided toolchain
with the ancient 8.3.0 version of gcc, after all... I'd have to admit
that I was initially reluctant to even investigate this, given the
tendency of Loongson people not verifying things on upstream versions of
their own work, but...
>
> Fixes: ad812c3bd65 ("linux-user: Implement CPU-specific signal handler for loongarch64 hosts")
> Reported-by: Song Gao <gaosong@loongson.cn>
> Suggested-by: Song Gao <gaosong@loongson.cn>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>  linux-user/host/loongarch64/host-signal.h | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/linux-user/host/loongarch64/host-signal.h b/linux-user/host/loongarch64/host-signal.h
> index 05e2c823717..7effa242515 100644
> --- a/linux-user/host/loongarch64/host-signal.h
> +++ b/linux-user/host/loongarch64/host-signal.h
> @@ -54,9 +54,7 @@ static inline bool host_signal_write(siginfo_t *info, ucontext_t *uc)
>          }
>          break;
>      case 0b001110: /* indexed, atomic, bounds-checking memory operations */
> -        uint32_t sel = (insn >> 15) & 0b11111111111;
> -
> -        switch (sel) {
> +        switch ((insn >> 15) & 0b11111111111) {
>          case 0b00000100000: /* stx.b */
>          case 0b00000101000: /* stx.h */
>          case 0b00000110000: /* stx.w */

the fix is obvious enough, doesn't harm readability, and solves a real
problem for some (their toolchain being outdated is not their fault,
rather Loongson's).

So after fixing the commit message:

Reviewed-by: WANG Xuerui <git@xen0n.name>

(Or do I just collect this patch and fix the commit message myself,
sending a pull request later? I'm new to QEMU maintenance procedure and
I'm still not quite sure if it is too heavyweight to have you send v2
for just a single typo and R-b tag collection.)