Re: [PATCH 2/4] linux-user/arm: Remove bogus SVC 0xf0002 handling

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

On 4/20/20 11:22 PM, Peter Maydell wrote:
> We incorrectly treat SVC 0xf0002 as a cacheflush request (which is a
> NOP for QEMU).  This is the wrong syscall number, because in the
> svc-immediate OABI syscall numbers are all offset by the
> ARM_SYSCALL_BASE value and so the correct insn is SVC 0x9f0002.
> (This is handled further down in the code with the other Arm-specific
> syscalls like NR_breakpoint.)
> 
> When this code was initially added in commit 6f1f31c069b20611 in
> 2004, ARM_NR_cacheflush was defined as (ARM_SYSCALL_BASE + 0xf0000 + 2)
> so the value in the comparison took account of the extra 0x900000
> offset. In commit fbb4a2e371f2fa7 in 2008, the ARM_SYSCALL_BASE
> was removed from the definition of ARM_NR_cacheflush and handling
> for this group of syscalls was added below the point where we subtract
> ARM_SYSCALL_BASE from the SVC immediate value. However that commit
> forgot to remove the now-obsolete earlier handling code.

I imagine you wrote this patch wearing an archeologist hat =)

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

> 
> Remove the spurious ARM_NR_cacheflush condition.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  linux-user/arm/cpu_loop.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/linux-user/arm/cpu_loop.c b/linux-user/arm/cpu_loop.c
> index 82d0dd3c312..025887d6b86 100644
> --- a/linux-user/arm/cpu_loop.c
> +++ b/linux-user/arm/cpu_loop.c
> @@ -308,9 +308,7 @@ void cpu_loop(CPUARMState *env)
>                      n = insn & 0xffffff;
>                  }
>  
> -                if (n == ARM_NR_cacheflush) {
> -                    /* nop */
> -                } else if (n == 0 || n >= ARM_SYSCALL_BASE || env->thumb) {
> +                if (n == 0 || n >= ARM_SYSCALL_BASE || env->thumb) {
>                      /* linux syscall */
>                      if (env->thumb || n == 0) {
>                          n = env->regs[7];
>