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authorFrans Kaashoek <[email protected]>2018-09-23 08:24:42 -0400
committerFrans Kaashoek <[email protected]>2018-09-23 08:35:30 -0400
commitab0db651af6f1ffa8fe96909ce16ae314d65c3fb (patch)
treec429f8ee36fa7da1e25f564a160b031613ca05e9 /main.c
parentb818915f793cd20c5d1e24f668534a9d690f3cc8 (diff)
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Checkpoint port of xv6 to x86-64. Passed usertests on 2 processors a few times.
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
Diffstat (limited to 'main.c')
-rw-r--r--main.c69
1 files changed, 28 insertions, 41 deletions
diff --git a/main.c b/main.c
index 9924e64..449396a 100644
--- a/main.c
+++ b/main.c
@@ -6,17 +6,22 @@
#include "proc.h"
#include "x86.h"
-static void startothers(void);
-static void mpmain(void) __attribute__((noreturn));
extern pde_t *kpgdir;
extern char end[]; // first address after kernel loaded from ELF file
+static void main(void) __attribute__((noreturn));
+static void startothers(void);
+
+
// Bootstrap processor starts running C code here.
// Allocate a real stack and switch to it, first
// doing some setup required for memory allocator to work.
int
-main(void)
+bpmain(uint64 mbmagic, uint64 mbaddr)
{
+ if(mbmagic != 0x2badb002)
+ panic("multiboot header not found");
+
kinit1(end, P2V(4*1024*1024)); // phys page allocator
kvmalloc(); // kernel page table
mpinit(); // detect other processors
@@ -30,26 +35,19 @@ main(void)
tvinit(); // trap vectors
binit(); // buffer cache
fileinit(); // file table
- ideinit(); // disk
+ ideinit(); // disk
+
startothers(); // start other processors
+
kinit2(P2V(4*1024*1024), P2V(PHYSTOP)); // must come after startothers()
userinit(); // first user process
- mpmain(); // finish this processor's setup
-}
-
-// Other CPUs jump here from entryother.S.
-static void
-mpenter(void)
-{
- switchkvm();
- seginit();
- lapicinit();
- mpmain();
+ main();
+ return 0;
}
// Common CPU setup code.
static void
-mpmain(void)
+main(void)
{
cprintf("cpu%d: starting %d\n", cpuid(), cpuid());
idtinit(); // load idt register
@@ -57,7 +55,17 @@ mpmain(void)
scheduler(); // start running processes
}
-pde_t entrypgdir[]; // For entry.S
+// Other CPUs jump here from entryother.S.
+void
+apmain(void)
+{
+ switchkvm();
+ seginit();
+ lapicinit();
+ main();
+}
+
+void apstart(void);
// Start the non-boot (AP) processors.
static void
@@ -72,7 +80,7 @@ startothers(void)
// The linker has placed the image of entryother.S in
// _binary_entryother_start.
code = P2V(0x7000);
- memmove(code, _binary_entryother_start, (uint)_binary_entryother_size);
+ memmove(code, _binary_entryother_start, (uint64)_binary_entryother_size);
for(c = cpus; c < cpus+ncpu; c++){
if(c == mycpu()) // We've started already.
@@ -82,9 +90,8 @@ startothers(void)
// pgdir to use. We cannot use kpgdir yet, because the AP processor
// is running in low memory, so we use entrypgdir for the APs too.
stack = kalloc();
- *(void**)(code-4) = stack + KSTACKSIZE;
- *(void(**)(void))(code-8) = mpenter;
- *(int**)(code-12) = (void *) V2P(entrypgdir);
+ *(uint32*)(code-4) = V2P(apstart);
+ *(uint64*)(code-12) = (uint64) (stack+KSTACKSIZE);
lapicstartap(c->apicid, V2P(code));
@@ -94,23 +101,3 @@ startothers(void)
}
}
-// The boot page table used in entry.S and entryother.S.
-// Page directories (and page tables) must start on page boundaries,
-// hence the __aligned__ attribute.
-// PTE_PS in a page directory entry enables 4Mbyte pages.
-
-__attribute__((__aligned__(PGSIZE)))
-pde_t entrypgdir[NPDENTRIES] = {
- // Map VA's [0, 4MB) to PA's [0, 4MB)
- [0] = (0) | PTE_P | PTE_W | PTE_PS,
- // Map VA's [KERNBASE, KERNBASE+4MB) to PA's [0, 4MB)
- [KERNBASE>>PDXSHIFT] = (0) | PTE_P | PTE_W | PTE_PS,
-};
-
-//PAGEBREAK!
-// Blank page.
-//PAGEBREAK!
-// Blank page.
-//PAGEBREAK!
-// Blank page.
-