Skeleton code for the page table translation project

P-Gu · Dec 25, 2022 · 47d9c27 · 47d9c27
1 parent b7c8467
commit 47d9c27
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Showing 7 changed files with 31 additions and 10 deletions.
diff --git a/apps/app.S b/apps/app.S
@@ -9,6 +9,7 @@
  .section .text
  .global _enter
 _enter:
+ lw a0, 0(a0) /* a0 should hold APPS_ARG, the address of integer argc */
  li sp,0x80002000
  call main
  call exit
diff --git a/earth/earth.c b/earth/earth.c
@@ -17,6 +17,8 @@ void tty_init();
 void disk_init();
 void intr_init();
 void mmu_init();
+
+struct grass *grass = (void*)APPS_STACK_TOP;
 struct earth *earth = (void*)GRASS_STACK_TOP;
 extern char bss_start, bss_end, data_rom, data_start, data_end;
 

diff --git a/grass/grass.c b/grass/grass.c
@@ -44,5 +44,7 @@ int main() {
  if (earth->platform == ARTY) earth->intr_enable();
 
  void (*sys_proc_entry)() = (void*)APPS_ENTRY;
+ asm("mv a0, %0" ::"r"(APPS_ARG));
+ asm("mv a1, %0" ::"r"(APPS_ARG + 4));
  sys_proc_entry();
 }
diff --git a/grass/process.h b/grass/process.h
@@ -6,9 +6,12 @@
 struct process{
  int pid;
  int status;
- void *sp, *mepc;
- int receiver_pid; /* used when status is PROC_WAIT_TO_SEND */
+ int receiver_pid; /* used when process is waiting to send a message */
+
+ void *mepc; /* machine exception program counter (mepc) */
+ void *sp_vaddr; /* used for switching stack between user / kernel */
 };
+
 extern int proc_curr_idx;
 extern struct process proc_set[MAX_NPROCESS];
 #define curr_pid proc_set[proc_curr_idx].pid

diff --git a/grass/scheduler.c b/grass/scheduler.c
@@ -48,22 +48,31 @@ void intr_entry(int id) {
  FATAL("intr_entry: got unknown interrupt #%d", id);
  }
 
- /* Switch to the grass kernel stack */
- ctx_start(&proc_set[proc_curr_idx].sp, (void*)GRASS_STACK_TOP);
+ /* Switch to the kernel stack */
+ ctx_start(&proc_set[proc_curr_idx].sp_vaddr, (void*)GRASS_STACK_TOP);
 }
 
 void ctx_entry() {
+ /* Switched to the kernel stack */
  int mepc, tmp;
  asm("csrr %0, mepc" : "=r"(mepc));
  proc_set[proc_curr_idx].mepc = (void*) mepc;
 
+ /* Student's code goes here: */
+ /* Save the interrupt stack */
+ /* Student's code ends here. */
+
  /* kernel_entry() is either proc_yield() or proc_syscall() */
  kernel_entry();
 
+ /* Student's code goes here: */
+ /* Restore the interrupt stack */
+ /* Student's code ends here. */
+
  /* Switch back to the user application stack */
  mepc = (int)proc_set[proc_curr_idx].mepc;
  asm("csrw mepc, %0" ::"r"(mepc));
- ctx_switch((void**)&tmp, proc_set[proc_curr_idx].sp);
+ ctx_switch((void**)&tmp, proc_set[proc_curr_idx].sp_vaddr);
 }
 
 static void proc_yield() {
@@ -97,7 +106,7 @@ static void proc_yield() {
  if (curr_status == PROC_READY) {
  proc_set_running(curr_pid);
  /* Prepare argc and argv */
- asm("mv a0, %0" ::"r"(*((int*)APPS_ARG)));
+ asm("mv a0, %0" ::"r"(APPS_ARG));
  asm("mv a1, %0" ::"r"(APPS_ARG + 4));
  /* Enter application code entry using mret */
  asm("csrw mepc, %0" ::"r"(APPS_ENTRY));

diff --git a/library/egos.h b/library/egos.h
@@ -29,6 +29,7 @@ struct earth {
  enum { QEMU, ARTY } platform;
 };
 
+#define MAX_NPROCESS 16
 struct grass {
  /* Process control interface */
  int (*proc_alloc)();
@@ -43,11 +44,13 @@ struct grass {
  /* Shell environment variables */
  int workdir_ino;
  char workdir[128];
+
+ /* Physical address of process stack, used in the page table project */
+ void* stack_paddr[MAX_NPROCESS];
 };
 
 extern struct earth *earth;
 extern struct grass *grass;
-#define MAX_NPROCESS 16
 
 #ifndef LIBC_STDIO
 #define printf earth->tty_printf
@@ -62,11 +65,11 @@ extern struct grass *grass;
 #define FRAME_CACHE_END 0x80020000
 #define FRAME_CACHE_START 0x80004000 /* 112KB frame cache */
  /* earth interface */
-#define GRASS_STACK_TOP 0x80003f80 /* 7KB earth/grass stack */
+#define GRASS_STACK_TOP 0x80003f80 /* 6KB earth/grass stack */
 #define SYSCALL_ARG 0x80002400 /* 1KB system call args */
- /*   grass interface */
+ /* 1KB grass interface */
 #define APPS_STACK_TOP 0x80002000 /* 6KB app stack */
-#define SAVED_INTR_STACK 0x80000400 /* 1KB saved interrupt stack */
+#define EXCP_STACK_OFFSET 0x00000400 /* 1KB saved exception stack */
 #define APPS_ARG 0x80000000 /* 1KB app main() argc, argv */
 #define APPS_SIZE 0x00003000 
 #define APPS_ENTRY 0x08005000 /* 12KB app code+data */

diff --git a/library/elf/elf.c b/library/elf/elf.c
@@ -63,6 +63,7 @@ static void load_app(int pid, elf_reader reader,
  /* Setup two pages for argc, argv and stack */
  earth->mmu_alloc(&frame_no, &base);
  earth->mmu_map(pid, stack_start++, frame_no);
+ grass->stack_paddr[pid] = (void*)(FRAME_CACHE_START + frame_no * PAGE_SIZE);
 
  int* argc_addr = (int*)base;
  int* argv_addr = argc_addr + 1;