abstract-machine(nemu): support context switch

abstract-machine/CMakeLists.txt

@@ -76,7 +76,8 @@ target_include_directories(
   INTERFACE $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/am/include>
             $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/am/src>
             $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
-target_compile_definitions(am_interface INTERFACE ARCH_H=<arch/${ISA}.h>)
+target_compile_definitions(am_interface INTERFACE ARCH_H=<arch/${ISA}.h>
+                                                  "__ISA__=\"${ISA}\"")
 file(GLOB_RECURSE AM_HEADERS "${CMAKE_SOURCE_DIR}/am/include/*.h")
 target_sources(
   am_interface

abstract-machine/am/include/arch/riscv.h

@@ -1,5 +1,6 @@
 #ifndef ARCH_H__
 #define ARCH_H__
+#include <stdint.h>
 
 #ifdef __riscv_e
 #define NR_REGS 16
@@ -9,10 +10,13 @@
 
 struct Context {
   // TODO: fix the order of these members to match trap.S
-  uintptr_t mepc, mcause, gpr[NR_REGS], mstatus;
+  uintptr_t gpr[NR_REGS];
+  uintptr_t mcause, mstatus, mepc;
   void *pdir;
 };
 
+enum Cause { CauseEnvironmentCallFromMMode = 11 };
+
 #ifdef __riscv_e
 #define GPR1 gpr[15] // a5
 #else

abstract-machine/am/src/platform/nemu/trm.c

@@ -6,7 +6,7 @@ int main(const char *args);
 
 Area heap = RANGE(&_heap_start, PMEM_END);
 #ifndef MAINARGS
-#define MAINARGS "5"
+#define MAINARGS "i"
 #endif
 static const char mainargs[] = MAINARGS;
 

abstract-machine/am/src/riscv/nemu/cte.c

@@ -1,14 +1,21 @@
+#include "arch/riscv.h"
 #include <am.h>
-#include <riscv/riscv.h>
 #include <klib.h>
+#include <riscv/riscv.h>
+#include <stdint.h>
 
-static Context* (*user_handler)(Event, Context*) = NULL;
+static Context *(*user_handler)(Event, Context *) = NULL;
 
-Context* __am_irq_handle(Context *c) {
+Context *__am_irq_handle(Context *c) {
   if (user_handler) {
     Event ev = {0};
     switch (c->mcause) {
-      default: ev.event = EVENT_ERROR; break;
+    case CauseEnvironmentCallFromMMode:
+      ev.event = EVENT_YIELD;
+      break;
+    default:
+      ev.event = EVENT_ERROR;
+      break;
     }
 
     c = user_handler(ev, c);
@@ -20,7 +27,7 @@ Context* __am_irq_handle(Context *c) {
 
 extern void __am_asm_trap(void);
 
-bool cte_init(Context*(*handler)(Event, Context*)) {
+bool cte_init(Context *(*handler)(Event, Context *)) {
   // initialize exception entry
   asm volatile("csrw mtvec, %0" : : "r"(__am_asm_trap));
 
@@ -31,7 +38,10 @@ bool cte_init(Context*(*handler)(Event, Context*)) {
 }
 
 Context *kcontext(Area kstack, void (*entry)(void *), void *arg) {
-  return NULL;
+  Context *c = kstack.end - sizeof(Context);
+  c->mepc = (uintptr_t)entry;
+  c->gpr[10] = (uintptr_t)arg;
+  return c;
 }
 
 void yield() {
@@ -42,9 +52,6 @@ void yield() {
 #endif
 }
 
-bool ienabled() {
-  return false;
-}
+bool ienabled() { return false; }
 
-void iset(bool enable) {
-}
+void iset(bool enable) {}

abstract-machine/am/src/riscv/nemu/trap.S

@@ -60,6 +60,8 @@ __am_asm_trap:
   mv a0, sp
   jal __am_irq_handle
 
+  mv sp, a0
+
   LOAD t1, OFFSET_STATUS(sp)
   LOAD t2, OFFSET_EPC(sp)
   csrw mstatus, t1

abstract-machine/default.nix

@@ -15,6 +15,9 @@ stdenv.mkDerivation {
     (lib.cmakeFeature "ISA" isa)
   ] ++ map (p: (lib.cmakeBool "__PLATFORM_${lib.strings.toUpper p}__" true)) platform;
 
+  cmakeBuildType = "Debug";
+  dontStrip = true;
+
   nativeBuildInputs = [
     cmake
   ];