kernel/entry.S

@@ -1,65 +1,21 @@
-# For a quick reference on RISC-V assembly:
+        # qemu -kernel loads the kernel at 0x80000000
-#   https://risc-v.guru/instructions/
+        # and causes each hart (i.e. CPU) to jump there.
-
+        # kernel.ld causes the following code to
-# Kernel entry point
+        # be placed at 0x80000000.
-#
-# qemu -kernel loads the kernel at 0x80000000
-# and causes each hart (i.e. CPU) to jump there.
-# kernel.ld causes the following code to
-# be placed at 0x80000000.
-
 .section .text
 .global _entry
 _entry:
-        # Clear all the registers.
-        li x1, 0x0
-        li x2, 0x0
-        li x3, 0x0
-        li x4, 0x0
-        li x5, 0x0
-        li x6, 0x0
-        li x7, 0x0
-        li x8, 0x0
-        li x9, 0x0
-        li x10, 0x0
-        li x11, 0x0
-        li x12, 0x0
-        li x13, 0x0
-        li x14, 0x0
-        li x15, 0x0
-        li x16, 0x0
-        li x17, 0x0
-        li x18, 0x0
-        li x19, 0x0
-        li x20, 0x0
-        li x21, 0x0
-        li x22, 0x0
-        li x23, 0x0
-        li x24, 0x0
-        li x25, 0x0
-        li x26, 0x0
-        li x27, 0x0
-        li x28, 0x0
-        li x29, 0x0
-        li x30, 0x0
-        li x31, 0x0
-
         # set up a stack for C.
         # stack0 is declared in start.c,
         # with a 4096-byte stack per CPU.
         # sp = stack0 + (hartid * 4096)
         la sp, stack0
-        li a0, 1024*4 # a0 = 4096
+        li a0, 1024*4
-
+        csrr a1, mhartid
-        # Control and Status Register Read
+        addi a1, a1, 1
-        csrr a1, mhartid # a1 = unique hart (core) id
+        mul a0, a0, a1
-        addi a1, a1, 1   # a1 += 1
+        add sp, sp, a0
-        mul a0, a0, a1   # a0 *= a1, aka a0 = 4096 * (hartid + 1), the base of the stack for this hart
-        add sp, sp, a0   # sp += a0, stack pointer is now properly configured
-
         # jump to start() in start.c
         call start
-
-# Infinite spin loop.
 spin:
         j spin

kernel/kernel.ld

@@ -9,11 +9,6 @@ SECTIONS
    */
   . = 0x80000000;
 
-  /*
-   * This section contains the code. This is, the machine language instructions
-   * that will be executed by the processor. In here we will find symbols
-   * that reference the functions in your object file.
-   */
   .text : {
     *(.text .text.*)
     . = ALIGN(0x1000);
@@ -24,10 +19,6 @@ SECTIONS
     PROVIDE(etext = .);
   }
 
-  /*
-   * This contains any data that is marked as read only.
-   * It is not unusual to find this data interleaved with the text section.
-   */
   .rodata : {
     . = ALIGN(16);
     *(.srodata .srodata.*) /* do not need to distinguish this from .rodata */
@@ -35,10 +26,6 @@ SECTIONS
     *(.rodata .rodata.*)
   }
 
-  /*
-   * This section contains initialized global and static variables.
-   * Any global object that has been explicitly initialized to a value different than zero.
-   */
   .data : {
     . = ALIGN(16);
     *(.sdata .sdata.*) /* do not need to distinguish this from .data */
@@ -46,12 +33,6 @@ SECTIONS
     *(.data .data.*)
   }
 
-  /*
-   * Contains all uninitialized global and static var iables. These are usually
-   * zeroed out by the startup code before we reach the main function. However,
-   * In an embedded system we usually provide our own startup code, which means
-   * we need to remember to do this ourselves.
-   */
   .bss : {
     . = ALIGN(16);
     *(.sbss .sbss.*) /* do not need to distinguish this from .bss */
@@ -59,6 +40,5 @@ SECTIONS
     *(.bss .bss.*)
   }
 
-  /* PROVIDE, see vm.c */
   PROVIDE(end = .);
 }

kernel/kernelvec.S

@@ -1,15 +1,11 @@
-# For a quick reference on RISC-V assembly:
+        #
-#   https://risc-v.guru/instructions/
+        # interrupts and exceptions while in supervisor
-
+        # mode come here.
-# Kernel trap handling
+        #
-#
+        # the current stack is a kernel stack.
-# interrupts and exceptions while in supervisor
+        # push all registers, call kerneltrap().
-# mode come here.
+        # when kerneltrap() returns, restore registers, return.
-#
+        #
-# the current stack is a kernel stack.
-# push all registers, call kerneltrap().
-# when kerneltrap() returns, restore registers, return.
-
 .globl kerneltrap
 .globl kernelvec
 .align 4
@@ -57,8 +53,7 @@ kernelvec:
         ld ra, 0(sp)
         ld sp, 8(sp)
         ld gp, 16(sp)
-        # Skip tp (thread pointer aka x4) (contains hartid)
+        # not tp (contains hartid), in case we moved CPUs
-        # in case we moved CPUs
         ld t0, 32(sp)
         ld t1, 40(sp)
         ld t2, 48(sp)
@@ -92,11 +87,9 @@ kernelvec:
         # return to whatever we were doing in the kernel.
         sret
 
-# machine-mode timer interrupt
+        #
-#
+        # machine-mode timer interrupt.
-# See: start.c for timervec declaration
+        #
-#   extern void timervec();
-
 .globl timervec
 .align 4
 timervec:
@@ -104,7 +97,7 @@ timervec:
         # scratch[0,8,16] : register save area.
         # scratch[24] : address of CLINT's MTIMECMP register.
         # scratch[32] : desired interval between interrupts.
-
+        
         csrrw a0, mscratch, a0
         sd a1, 0(a0)
         sd a2, 8(a0)

kernel/start.c

@@ -2,6 +2,7 @@
 #include "param.h"
 #include "memlayout.h"
 #include "riscv.h"
+#include "defs.h"
 
 void main();
 void timerinit();

kernel/swtch.S

@@ -1,18 +1,12 @@
-# For a quick reference on RISC-V assembly:
-#   https://risc-v.guru/instructions/
-
 # Context switch
 #
-# Save current registers in old. Load from new.
-#
-# See: defs.h for swtch declaration
-# See: proc.h for struct context definition
-#
 #   void swtch(struct context *old, struct context *new);
+# 
+# Save current registers in old. Load from new.
+
 
 .globl swtch
 swtch:
-        # sd = Store Double (64 bits)
         sd ra, 0(a0)
         sd sp, 8(a0)
         sd s0, 16(a0)
@@ -28,7 +22,6 @@ swtch:
         sd s10, 96(a0)
         sd s11, 104(a0)
 
-        # ld = Load Double (64 bits)
         ld ra, 0(a1)
         ld sp, 8(a1)
         ld s0, 16(a1)
@@ -43,7 +36,7 @@ swtch:
         ld s9, 88(a1)
         ld s10, 96(a1)
         ld s11, 104(a1)
-
+        
         ret
 
 

kernel/trampoline.S

@@ -1,17 +1,14 @@
-# For a quick reference on RISC-V assembly:
+        #
-#   https://risc-v.guru/instructions/
+        # low-level code to handle traps from user space into
-
+        # the kernel, and returns from kernel to user.
-# Trampoline code
+        #
-#
+        # the kernel maps the page holding this code
-# low-level code to handle traps from user space into
+        # at the same virtual address (TRAMPOLINE)
-# the kernel, and returns from kernel to user.
+        # in user and kernel space so that it continues
-#
+        # to work when it switches page tables.
-# the kernel maps the page holding this code
+        # kernel.ld causes this code to start at 
-# at the same virtual address (TRAMPOLINE)
+        # a page boundary.
-# in user and kernel space so that it continues
+        #
-# to work when it switches page tables.
-# kernel.ld causes this code to start at
-# a page boundary.
 
 #include "riscv.h"
 #include "memlayout.h"
@@ -21,7 +18,7 @@
 trampoline:
 .align 4
 .globl uservec
-uservec:
+uservec:    
 	#
         # trap.c sets stvec to point here, so
         # traps from user space start here,
@@ -37,7 +34,7 @@ uservec:
         # but it's mapped to the same virtual address
         # (TRAPFRAME) in every process's user page table.
         li a0, TRAPFRAME
-
+        
         # save the user registers in TRAPFRAME
         sd ra, 40(a0)
         sd sp, 48(a0)
@@ -148,7 +145,7 @@ userret:
 
 	# restore user a0
         ld a0, 112(a0)
-
+        
         # return to user mode and user pc.
         # usertrapret() set up sstatus and sepc.
         sret

user/initcode.S

@@ -1,6 +1,3 @@
-# For a quick reference on RISC-V assembly:
-#   https://risc-v.guru/instructions/
-
 # Initial process that execs /init.
 # This code runs in user space.
 

user/mkdir.c

@@ -1,3 +1,5 @@
+#include "kernel/types.h"
+#include "kernel/stat.h"
 #include "user/user.h"
 
 int