ab0db651af
The x86-64 doesn't just add two levels to page tables to support 64 bit addresses, but is a different processor. For example, calling conventions, system calls, and segmentation are different from 32-bit x86. Segmentation is basically gone, but gs/fs in combination with MSRs can be used to hold a per-core pointer. In general, x86-64 is more straightforward than 32-bit x86. The port uses code from sv6 and the xv6 "rsc-amd64" branch. A summary of the changes is as follows: - Booting: switch to grub instead of xv6's bootloader (pass -kernel to qemu), because xv6's boot loader doesn't understand 64bit ELF files. And, we don't care anymore about booting. - Makefile: use -m64 instead of -m32 flag for gcc, delete boot loader, xv6.img, bochs, and memfs. For now dont' use -O2, since usertests with -O2 is bigger than MAXFILE! - Update gdb.tmpl to be for i386 or x86-64 - Console/printf: use stdarg.h and treat 64-bit addresses different from ints (32-bit) - Update elfhdr to be 64 bit - entry.S/entryother.S: add code to switch to 64-bit mode: build a simple page table in 32-bit mode before switching to 64-bit mode, share code for entering boot processor and APs, and tweak boot gdt. The boot gdt is the gdt that the kernel proper also uses. (In 64-bit mode, the gdt/segmentation and task state mostly disappear.) - exec.c: fix passing argv (64-bit now instead of 32-bit). - initcode.c: use syscall instead of int. - kernel.ld: load kernel very high, in top terabyte. 64 bits is a lot of address space! - proc.c: initial return is through new syscall path instead of trapret. - proc.h: update struct cpu to have some scratch space since syscall saves less state than int, update struct context to reflect x86-64 calling conventions. - swtch: simplify for x86-64 calling conventions. - syscall: add fetcharg to handle x86-64 calling convetions (6 arguments are passed through registers), and fetchaddr to read a 64-bit value from user space. - sysfile: update to handle pointers from user space (e.g., sys_exec), which are 64 bits. - trap.c: no special trap vector for sys calls, because x86-64 has a different plan for system calls. - trapasm: one plan for syscalls and one plan for traps (interrupt and exceptions). On x86-64, the kernel is responsible for switching user/kernel stacks. To do, xv6 keeps some scratch space in the cpu structure, and uses MSR GS_KERN_BASE to point to the core's cpu structure (using swapgs). - types.h: add uint64, and change pde_t to uint64 - usertests: exit() when fork fails, which helped in tracking down one of the bugs in the switch from 32-bit to 64-bit - vectors: update to make them 64 bits - vm.c: use bootgdt in kernel too, program MSRs for syscalls and core-local state (for swapgs), walk 4 levels in walkpgdir, add DEVSPACETOP, use task segment to set kernel stack for interrupts (but simpler than in 32-bit mode), add an extra argument to freevm (size of user part of address space) to avoid checking all entries till KERNBASE (there are MANY TB before the top 1TB). - x86: update trapframe to have 64-bit entries, which is what the processor pushes on syscalls and traps. simplify lgdt and lidt, using struct desctr, which needs the gcc directives packed and aligned. TODO: - use int32 instead of int? - simplify curproc(). xv6 has per-cpu state again, but this time it must have it. - avoid repetition in walkpgdir - fix validateint() in usertests.c - fix bugs (e.g., observed one a case of entering kernel with invalid gs or proc
99 lines
2.2 KiB
C
99 lines
2.2 KiB
C
// Physical memory allocator, intended to allocate
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// memory for user processes, kernel stacks, page table pages,
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// and pipe buffers. Allocates 4096-byte pages.
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#include "types.h"
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#include "defs.h"
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#include "param.h"
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#include "memlayout.h"
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#include "mmu.h"
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#include "spinlock.h"
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void freerange(void *vstart, void *vend);
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extern char end[]; // first address after kernel loaded from ELF file
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// defined by the kernel linker script in kernel.ld
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struct run {
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struct run *next;
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};
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struct {
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struct spinlock lock;
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int use_lock;
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struct run *freelist;
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} kmem;
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// Initialization happens in two phases.
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// 1. main() calls kinit1() while still using entrypgdir to place just
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// the pages mapped by entrypgdir on free list.
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// 2. main() calls kinit2() with the rest of the physical pages
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// after installing a full page table that maps them on all cores.
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void
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kinit1(void *vstart, void *vend)
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{
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initlock(&kmem.lock, "kmem");
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kmem.use_lock = 0;
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freerange(vstart, vend);
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}
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void
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kinit2(void *vstart, void *vend)
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{
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freerange(vstart, vend);
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kmem.use_lock = 1;
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}
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void
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freerange(void *vstart, void *vend)
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{
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char *p;
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p = (char*)PGROUNDUP((uint64)vstart);
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for(; p + PGSIZE <= (char*)vend; p += PGSIZE)
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kfree(p);
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}
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//PAGEBREAK: 21
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// Free the page of physical memory pointed at by v,
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// which normally should have been returned by a
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// call to kalloc(). (The exception is when
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// initializing the allocator; see kinit above.)
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void
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kfree(char *v)
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{
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struct run *r;
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if((uint64)v % PGSIZE || v < end || V2P(v) >= PHYSTOP)
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panic("kfree");
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// Fill with junk to catch dangling refs.
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memset(v, 1, PGSIZE);
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if(kmem.use_lock)
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acquire(&kmem.lock);
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r = (struct run*)v;
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r->next = kmem.freelist;
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kmem.freelist = r;
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if(kmem.use_lock)
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release(&kmem.lock);
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}
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// Allocate one 4096-byte page of physical memory.
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// Returns a pointer that the kernel can use.
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// Returns 0 if the memory cannot be allocated.
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char*
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kalloc(void)
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{
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struct run *r;
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if(kmem.use_lock)
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acquire(&kmem.lock);
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r = kmem.freelist;
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if(r)
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kmem.freelist = r->next;
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if(kmem.use_lock)
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release(&kmem.lock);
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if(r != 0 && (uint64) r < KERNBASE)
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panic("kalloc");
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return (char*)r;
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}
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