diff options
author | Frans Kaashoek <[email protected]> | 2018-09-29 08:30:50 -0400 |
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committer | Frans Kaashoek <[email protected]> | 2018-09-29 08:34:41 -0400 |
commit | 3bfcaeaf015ffe0d92937c023e9a0086909a0161 (patch) | |
tree | da9f7348ceff53f913ce82209e91959a8c347ebd | |
parent | 322990649b35c893931a9ce67d4ccb25883c7446 (diff) | |
download | xv6-labs-3bfcaeaf015ffe0d92937c023e9a0086909a0161.tar.gz xv6-labs-3bfcaeaf015ffe0d92937c023e9a0086909a0161.tar.bz2 xv6-labs-3bfcaeaf015ffe0d92937c023e9a0086909a0161.zip |
Make sysexit and trapret paths the same, so that forkret can return through
either path. This helped tracking down a bug: use 144 instead of 32 to find cs
in trapframe so that gs is correctly saved and restored.
For good measure update linker script, because newer versions of GCC sometimes
places symbols passed end.
-rw-r--r-- | kernel.ld | 7 | ||||
-rw-r--r-- | proc.c | 16 | ||||
-rw-r--r-- | trapasm.S | 11 |
3 files changed, 22 insertions, 12 deletions
@@ -41,9 +41,10 @@ SECTIONS .data : { *(.data) } - PROVIDE(edata = .); - .bss : { + bss : { + PROVIDE(edata = .); *(.bss) + *(COMMON) + PROVIDE(end = .); } - PROVIDE(end = .); } @@ -6,7 +6,6 @@ #include "x86.h" #include "proc.h" #include "spinlock.h" -#include "msr.h" struct { struct spinlock lock; @@ -17,7 +16,11 @@ static struct proc *initproc; int nextpid = 1; extern void forkret(void); + +// we can return two ways out of the kernel and +// for new processes we can choose either way extern void sysexit(void); +extern void trapret(void); static void wakeup1(void *chan); @@ -101,6 +104,10 @@ found: // Leave room for trap frame. sp -= sizeof *p->tf; + + if ((uint64) sp % 16) + panic("misaligned sp"); + p->tf = (struct trapframe*)sp; // Set up new context to start executing at forkret, @@ -132,6 +139,8 @@ userinit(void) inituvm(p->pgdir, _binary_initcode_start, (uint64)_binary_initcode_size); p->sz = PGSIZE; memset(p->tf, 0, sizeof(*p->tf)); + p->tf->cs = UCSEG | 0x3; + p->tf->ss = UDSEG | 0x3; p->tf->r11 = FL_IF; p->tf->rsp = PGSIZE; p->tf->rcx = 0; // beginning of initcode.S @@ -321,12 +330,12 @@ scheduler(void) { struct proc *p; struct cpu *c = mycpu(); + c->proc = 0; - for(;;){ // Enable interrupts on this processor. sti(); - + // Loop over process table looking for process to run. acquire(&ptable.lock); for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){ @@ -336,7 +345,6 @@ scheduler(void) // Switch to chosen process. It is the process's job // to release ptable.lock and then reacquire it // before jumping back to us. - c->proc = p; switchuvm(p); p->state = RUNNING; @@ -22,7 +22,7 @@ alltraps: push %rbx push %rax - cmpw $KCSEG, 32(%rsp) # compare to saved cs + cmpw $KCSEG, 144(%rsp) # compare to saved cs jz 1f swapgs @@ -33,7 +33,7 @@ alltraps: .globl trapret trapret: cli - cmpw $KCSEG, 32(%rsp) # compare to saved cs + cmpw $KCSEG, 144(%rsp) # compare to saved cs jz 1f swapgs @@ -72,12 +72,12 @@ sysentry: # Build trap frame. movq %rax, %rsp movq %gs:0, %rax // restore rax - // push usp - push $0 + // push usp to make a valid trapframe + push $(UDSEG|0x3) push %gs:8 // safe eflags and eip push %r11 - push $UCSEG + push $(UCSEG|0x3) push %rcx // push errno and trapno to make stack look like a trap push $0 @@ -130,6 +130,7 @@ sysexit: add $(5*8), %rsp # discard trapnum, errorcode, rip, cs and rflags mov (%rsp),%rsp # switch to the user stack + # there are two more values on the stack, but we don't care about them swapgs sysretq |