Re: [PATCH 3/8] accel/tcg: Support TCG_TARGET_SIGNED_ADDR32 for softmmu

[WANG Xuerui]

Hi Richard,

On 2021/10/11 01:43, Richard Henderson wrote:
> When TCG_TARGET_SIGNED_ADDR32 is set, adjust the tlb addend to
> allow the 32-bit guest address to be sign extended within the
> 64-bit host register instead of zero extended.
>
> This will simplify tcg hosts like MIPS, RISC-V, and LoongArch,
> which naturally sign-extend 32-bit values, in contrast to x86_64
> and AArch64 which zero-extend them.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  accel/tcg/cputlb.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/accel/tcg/cputlb.c b/accel/tcg/cputlb.c
> index 761f726722..d12621c60e 100644
> --- a/accel/tcg/cputlb.c
> +++ b/accel/tcg/cputlb.c
> @@ -39,6 +39,7 @@
>  #ifdef CONFIG_PLUGIN
>  #include "qemu/plugin-memory.h"
>  #endif
> +#include "tcg-target-sa32.h"
>  
>  /* DEBUG defines, enable DEBUG_TLB_LOG to log to the CPU_LOG_MMU target */
>  /* #define DEBUG_TLB */
> @@ -92,6 +93,9 @@ static inline size_t sizeof_tlb(CPUTLBDescFast *fast)
>  
>  static inline uintptr_t g2h_tlbe(const CPUTLBEntry *tlb, target_ulong gaddr)
>  {
> +    if (TCG_TARGET_SIGNED_ADDR32 && TARGET_LONG_BITS == 32) {
It seems this branch's direction should always match that of the branch
added below, so if TARGET_LONG_BITS == TARGET_LONG_BITS == 32 this
invariant is broken? Or is this expected behavior?
> +        return tlb->addend + (int32_t)gaddr;
> +    }
>      return tlb->addend + (uintptr_t)gaddr;
>  }
>  
> @@ -1234,7 +1238,13 @@ void tlb_set_page_with_attrs(CPUState *cpu, 
> target_ulong vaddr,
>      desc->iotlb[index].attrs = attrs;
>  
>      /* Now calculate the new entry */
> -    tn.addend = addend - vaddr_page;
> +
> +    if (TCG_TARGET_SIGNED_ADDR32 && TARGET_LONG_BITS < TCG_TARGET_REG_BITS) {
> +        tn.addend = addend - (int32_t)vaddr_page;
> +    } else {
> +        tn.addend = addend - vaddr_page;
> +    }
> +
>      if (prot & PAGE_READ) {
>          tn.addr_read = address;
>          if (wp_flags & BP_MEM_READ) {