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Bring back the save/restore of the %ds, %es, %fs and %gs registers for

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the 32bit images on amd64.

Change the semantic of the PCB_32BIT pcb flag to request the context
switch code to operate on the segment registers. Its previous meaning
of saving or restoring the %gs base offset is assigned to the new
PCB_GS32BIT flag.

FreeBSD 32bit image activator sets the PCB_32BIT flag, while Linux 32bit
emulation sets PCB_32BIT | PCB_GS32BIT.

Reviewed by:	peter
MFC after:	2 weeks
This commit is contained in:
kib 2008-07-30 11:30:55 +00:00
parent 13b6ce6962
commit 19bf5e2807
5 changed files with 33 additions and 20 deletions

47
sys/amd64/amd64/cpu_switch.S

@ -113,8 +113,8 @@ ENTRY(cpu_switch)
movq PCB_GSBASE(%r8),%r10
testl $PCB_32BIT,PCB_FLAGS(%r8)
jnz store_gs /* static predict not taken */
done_store_gs:
jnz store_seg
done_store_seg:
testl $PCB_DBREGS,PCB_FLAGS(%r8)
jnz store_dr /* static predict not taken */
@ -176,6 +176,10 @@ sw1:
testl $TDP_KTHREAD,TD_PFLAGS(%rsi)
jnz do_kthread
testl $PCB_32BIT,PCB_FLAGS(%r8)
jnz load_seg
done_load_seg:
cmpq PCB_FSBASE(%r8),%r9
jz 1f
/* Restore userland %fs */
@ -184,7 +188,6 @@ sw1:
movl PCB_FSBASE+4(%r8),%edx
wrmsr
1:
cmpq PCB_GSBASE(%r8),%r10
jz 2f
/* Restore userland %gs */
@ -193,8 +196,8 @@ sw1:
movl PCB_GSBASE+4(%r8),%edx
wrmsr
2:
do_tss:
do_tss:
/* Update the TSS_RSP0 pointer for the next interrupt */
movq PCPU(TSSP), %rax
movq %r8, PCPU(RSP0)
@ -208,10 +211,6 @@ do_tss:
jnz load_dr /* static predict not taken */
done_load_dr:
testl $PCB_32BIT,PCB_FLAGS(%r8)
jnz load_gs /* static predict not taken */
done_load_gs:
/* Restore context. */
movq PCB_R15(%r8),%r15
movq PCB_R14(%r8),%r14
@ -243,23 +242,35 @@ do_kthread:
movq %r10,PCB_GSBASE(%r8)
jmp do_tss
store_gs:
store_seg:
movl %gs,PCB_GS(%r8)
movq PCB_GS32P(%r8),%rax
testl $PCB_GS32BIT,PCB_FLAGS(%r8)
jnz 2f
1: movl %ds,PCB_DS(%r8)
movl %es,PCB_ES(%r8)
movl %fs,PCB_FS(%r8)
jmp done_store_seg
2: movq PCB_GS32P(%r8),%rax
movq (%rax),%rax
movq %rax,PCB_GS32SD(%r8)
jmp done_store_gs
jmp 1b
load_gs:
/* Restore userland %gs while preserving kernel gsbase */
movq PCB_GS32P(%r8),%rax
movq PCB_GS32SD(%r8),%rcx
movq %rcx,(%rax)
movl $MSR_GSBASE,%ecx
load_seg:
testl $PCB_GS32BIT,PCB_FLAGS(%r8)
jnz 2f
1: movl $MSR_GSBASE,%ecx
rdmsr
movl PCB_GS(%r8),%gs
wrmsr
jmp done_load_gs
movl PCB_DS(%r8),%ds
movl PCB_ES(%r8),%es
movl PCB_FS(%r8),%fs
jmp done_load_seg
/* Restore userland %gs while preserving kernel gsbase */
2: movq PCB_GS32P(%r8),%rax
movq PCB_GS32SD(%r8),%rcx
movq %rcx,(%rax)
jmp 1b
store_dr:
movq %dr7,%rax /* yes, do the save */

1
sys/amd64/amd64/genassym.c

@ -140,6 +140,7 @@ ASSYM(PCB_DR6, offsetof(struct pcb, pcb_dr6));
ASSYM(PCB_DR7, offsetof(struct pcb, pcb_dr7));
ASSYM(PCB_DBREGS, PCB_DBREGS);
ASSYM(PCB_32BIT, PCB_32BIT);
ASSYM(PCB_GS32BIT, PCB_GS32BIT);
ASSYM(PCB_FULLCTX, PCB_FULLCTX);
ASSYM(PCB_FLAGS, offsetof(struct pcb, pcb_flags));

2
sys/amd64/ia32/ia32_signal.c

@ -741,6 +741,6 @@ ia32_setregs(td, entry, stack, ps_strings)
fpstate_drop(td);
/* Return via doreti so that we can change to a different %cs */
pcb->pcb_flags |= PCB_FULLCTX;
pcb->pcb_flags |= PCB_FULLCTX | PCB_32BIT;
td->td_retval[1] = 0;
}

1
sys/amd64/include/pcb.h

@ -70,6 +70,7 @@ struct pcb {
struct savefpu pcb_save;
#define PCB_DBREGS 0x02 /* process using debug registers */
#define PCB_FPUINITDONE 0x08 /* fpu state is initialized */
#define PCB_GS32BIT 0x20 /* linux gs switch */
#define PCB_32BIT 0x40 /* process has 32 bit context (segs etc) */
#define PCB_FULLCTX 0x80 /* full context restore on sysret */

2
sys/amd64/linux32/linux32_machdep.c

@ -696,7 +696,7 @@ linux_clone(struct thread *td, struct linux_clone_args *args)
td2->td_pcb->pcb_gs32sd = sd;
td2->td_pcb->pcb_gs32p = &gdt[GUGS32_SEL];
td2->td_pcb->pcb_gs = GSEL(GUGS32_SEL, SEL_UPL);
td2->td_pcb->pcb_flags |= PCB_32BIT;
td2->td_pcb->pcb_flags |= PCB_GS32BIT | PCB_32BIT;
}
}