2009-07-12 02:28:29 +00:00
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# Context switch
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#
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2019-05-31 13:45:59 +00:00
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# void swtch(struct context *old, struct context *new);
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2009-07-12 02:28:29 +00:00
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#
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2019-05-31 13:45:59 +00:00
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# Save current registers in old. Load from new.
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2007-08-28 12:48:33 +00:00
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.globl swtch
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swtch:
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2019-05-31 13:45:59 +00:00
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sd ra, 0(a0)
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sd sp, 8(a0)
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sd s0, 16(a0)
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sd s1, 24(a0)
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sd s2, 32(a0)
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sd s3, 40(a0)
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sd s4, 48(a0)
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sd s5, 56(a0)
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sd s6, 64(a0)
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sd s7, 72(a0)
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sd s8, 80(a0)
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sd s9, 88(a0)
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sd s10, 96(a0)
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sd s11, 104(a0)
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2007-08-28 12:48:33 +00:00
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2019-05-31 13:45:59 +00:00
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ld ra, 0(a1)
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ld sp, 8(a1)
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ld s0, 16(a1)
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ld s1, 24(a1)
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ld s2, 32(a1)
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ld s3, 40(a1)
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ld s4, 48(a1)
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ld s5, 56(a1)
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ld s6, 64(a1)
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ld s7, 72(a1)
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ld s8, 80(a1)
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ld s9, 88(a1)
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ld s10, 96(a1)
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ld s11, 104(a1)
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ret
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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
2018-09-23 12:24:42 +00:00
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