On 8/8/21 3:45 PM, LIU Zhiwei wrote:
On 2021/8/6 上午3:06, Richard Henderson wrote:
On 8/4/21 4:53 PM, LIU Zhiwei wrote:
+static TCGv gpr_src_u(DisasContext *ctx, int reg_num)
+{
+ if (reg_num == 0) {
+ return ctx->zero;
+ }
+ if (ctx->uxl32) {
+ tcg_gen_ext32u_tl(cpu_gpr[reg_num], cpu_gpr[reg_num]);
+ }
+ return cpu_gpr[reg_num];
+}
+
+static TCGv gpr_src_s(DisasContext *ctx, int reg_num)
+{
+ if (reg_num == 0) {
+ return ctx->zero;
+ }
+ if (ctx->uxl32) {
+ tcg_gen_ext32s_tl(cpu_gpr[reg_num], cpu_gpr[reg_num]);
+ }
+ return cpu_gpr[reg_num];
+}
This is bad: you cannot modify the source registers like this.
In my opinion, when uxl32, the only meaningful part is the low 32 bits, and it doesn't
matter to modify the high parts.
Then why does the architecture manual specify that when registers are modified the value
written sign-extended? This effect should be visible...
These incorrect modifications will be visible to the kernel on transition back
to S-mode.
When transition back to S-mode, I think the kernel will save the U-mode
registers to memory.
... here. Once we're in S-mode, we have SXLEN, and if SXLEN > UXLEN, the high part of the
register will be visible. It really must be either (1) sign-extended because U-mode wrote
to the register or (2) unmodified from the last time S-mode wrote to the register.
r~
