*-nemu,cte: support _kcontext() with arg

am/src/mips32/nemu/cte.c

@@ -61,6 +61,7 @@ int _cte_init(_Context*(*handler)(_Event, _Context*)) {
 _Context *_kcontext(_Area kstack, void (*entry)(void *), void *arg) {
   _Context *c = (_Context*)kstack.end - 1;
   c->epc = (uintptr_t)entry;
+  c->GPR2 = (uintptr_t)arg; // a0
   return c;
 }
 

am/src/riscv32/nemu/cte.c

@@ -49,6 +49,7 @@ _Context *_kcontext(_Area kstack, void (*entry)(void *), void *arg) {
   _Context *c = (_Context*)kstack.end - 1;
 
   c->epc = (uintptr_t)entry;
+  c->GPR2 = (uintptr_t)arg;
   c->status = 0x000c0100;
   return c;
 }

am/src/x86/nemu/cte.c

@@ -63,11 +63,15 @@ int _cte_init(_Context*(*handler)(_Event, _Context*)) {
   return 0;
 }
 
+void __am_kcontext_start();
+
 _Context* _kcontext(_Area kstack, void (*entry)(void *), void *arg) {
   _Context *c = (_Context *)kstack.end - 1;
   c->cs = 0x8;
-  c->eip = (uintptr_t)entry;
+  c->eip = (uintptr_t)__am_kcontext_start;
   c->eflags = 0x2 | FL_IF;
+  c->GPR1 = (uintptr_t)arg;
+  c->GPR2 = (uintptr_t)entry;
   return c;
 }
 

am/src/x86/nemu/trap.S

@@ -4,6 +4,11 @@
 .globl __am_irq0;        __am_irq0:  pushl $0;  pushl   $32; jmp __am_asm_trap
 .globl __am_vecnull;  __am_vecnull:  pushl $0;  pushl   $-1; jmp __am_asm_trap
 
+.globl __am_kcontext_start
+__am_kcontext_start:
+  pushl %eax
+  call *%ebx
+
 __am_asm_trap:
   pushal