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
64 lines
2.4 KiB
C
64 lines
2.4 KiB
C
// Per-CPU state
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struct cpu {
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uint64 syscallno; // Temporary used by sysentry
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uint64 usp; // Temporary used by sysentry
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struct proc *proc; // The process running on this cpu or null
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uchar apicid; // Local APIC ID
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struct context *scheduler; // swtch() here to enter scheduler
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struct taskstate ts; // Used by x86 to find stack for interrupt
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struct segdesc gdt[NSEGS]; // x86 global descriptor table
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volatile uint started; // Has the CPU started?
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int ncli; // Depth of pushcli nesting.
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int intena; // Were interrupts enabled before pushcli?
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};
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extern struct cpu cpus[NCPU];
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extern int ncpu;
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//PAGEBREAK: 17
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// Saved registers for kernel context switches.
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// Don't need to save all the segment registers (%cs, etc),
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// because they are constant across kernel contexts.
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// Don't need to save %eax, %ecx, %edx, because the
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// x86 convention is that the caller has saved them.
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// Contexts are stored at the bottom of the stack they
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// describe; the stack pointer is the address of the context.
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// The layout of the context matches the layout of the stack in swtch.S
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// at the "Switch stacks" comment. Switch doesn't save eip explicitly,
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// but it is on the stack and allocproc() manipulates it.
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struct context {
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uint64 r15;
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uint64 r14;
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uint64 r13;
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uint64 r12;
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uint64 r11;
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uint64 rbx;
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uint64 ebp; //rbp
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uint64 eip; //rip;
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};
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enum procstate { UNUSED, EMBRYO, SLEEPING, RUNNABLE, RUNNING, ZOMBIE };
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// Per-process state
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struct proc {
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char *kstack; // Bottom of kernel stack for this process, must be first entry
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uint64 sz; // Size of process memory (bytes)
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pde_t* pgdir; // Page table
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enum procstate state; // Process state
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int pid; // Process ID
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struct proc *parent; // Parent process
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struct trapframe *tf; // Trap frame for current syscall
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struct context *context; // swtch() here to run process
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void *chan; // If non-zero, sleeping on chan
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int killed; // If non-zero, have been killed
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struct file *ofile[NOFILE]; // Open files
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struct inode *cwd; // Current directory
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char name[16]; // Process name (debugging)
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};
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// Process memory is laid out contiguously, low addresses first:
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// text
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// original data and bss
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// fixed-size stack
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// expandable heap
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