Some clarifications and updates for the comments, mostly retrieved
from Bruce Evans. Trim the trailing spaces. MFC after: 1 week
This commit is contained in:
Konstantin Belousov
parent
a0b9cbc8a2
commit
c788f92509
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=251988
@ -80,18 +80,22 @@ dtrace_invop_calltrap_addr:
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* This is equivalent to the i386 port's use of SDT_SYS386TGT.
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*
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* The cpu will push a certain amount of state onto the kernel stack for
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* the current process. See amd64/include/frame.h.
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* This includes the current RFLAGS (status register, which includes
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* the current process. See amd64/include/frame.h.
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* This includes the current RFLAGS (status register, which includes
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* the interrupt disable state prior to the trap), the code segment register,
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* and the return instruction pointer are pushed by the cpu. The cpu
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* will also push an 'error' code for certain traps. We push a dummy
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* error code for those traps where the cpu doesn't in order to maintain
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* and the return instruction pointer are pushed by the cpu. The cpu
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* will also push an 'error' code for certain traps. We push a dummy
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* error code for those traps where the cpu doesn't in order to maintain
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* a consistent frame. We also push a contrived 'trap number'.
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*
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* The cpu does not push the general registers, we must do that, and we
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* must restore them prior to calling 'iret'. The cpu adjusts the %cs and
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* %ss segment registers, but does not mess with %ds, %es, or %fs. Thus we
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* must load them with appropriate values for supervisor mode operation.
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* The CPU does not push the general registers, so we must do that, and we
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* must restore them prior to calling 'iret'. The CPU adjusts %cs and %ss
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* but does not mess with %ds, %es, %gs or %fs. We swap the %gs base for
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* for the kernel mode operation shortly, without changes to the selector
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* loaded. Since superuser long mode works with any selectors loaded into
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* segment registers other then %cs, which makes them mostly unused in long
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* mode, and kernel does not reference %fs, leave them alone. The segment
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* registers are reloaded on return to the usermode.
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*/
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MCOUNT_LABEL(user)
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@ -503,7 +507,7 @@ nmi_calltrap:
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#ifdef HWPMC_HOOKS
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/*
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* Capture a userspace callchain if needed.
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*
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*
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* - Check if the current trap was from user mode.
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* - Check if the current thread is valid.
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* - Check if the thread requires a user call chain to be
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@ -549,7 +553,7 @@ outofnmi:
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* At this point the processor has exited NMI mode and is running
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* with interrupts turned off on the normal kernel stack.
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*
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* If a pending NMI gets recognized at or after this point, it
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* If a pending NMI gets recognized at or after this point, it
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* will cause a kernel callchain to be traced.
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*
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* We turn interrupts back on, and call the user callchain capture hook.
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@ -567,7 +571,7 @@ nocallchain:
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#endif
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testl %ebx,%ebx
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jnz doreti_exit
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nmi_kernelexit:
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nmi_kernelexit:
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/*
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* Put back the preserved MSR_GSBASE value.
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*/
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@ -54,13 +54,13 @@
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.globl dtrace_invop_jump_addr
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.align 4
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.type dtrace_invop_jump_addr, @object
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.size dtrace_invop_jump_addr, 4
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.size dtrace_invop_jump_addr, 4
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dtrace_invop_jump_addr:
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.zero 4
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.globl dtrace_invop_calltrap_addr
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.align 4
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.type dtrace_invop_calltrap_addr, @object
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.size dtrace_invop_calltrap_addr, 4
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.size dtrace_invop_calltrap_addr, 4
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dtrace_invop_calltrap_addr:
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.zero 8
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#endif
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@ -75,22 +75,22 @@ dtrace_invop_calltrap_addr:
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* Trap and fault vector routines.
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*
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* Most traps are 'trap gates', SDT_SYS386TGT. A trap gate pushes state on
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* the stack that mostly looks like an interrupt, but does not disable
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* interrupts. A few of the traps we are use are interrupt gates,
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* the stack that mostly looks like an interrupt, but does not disable
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* interrupts. A few of the traps we are use are interrupt gates,
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* SDT_SYS386IGT, which are nearly the same thing except interrupts are
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* disabled on entry.
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*
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* The cpu will push a certain amount of state onto the kernel stack for
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* the current process. The amount of state depends on the type of trap
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* and whether the trap crossed rings or not. See i386/include/frame.h.
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* At the very least the current EFLAGS (status register, which includes
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* the current process. The amount of state depends on the type of trap
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* and whether the trap crossed rings or not. See i386/include/frame.h.
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* At the very least the current EFLAGS (status register, which includes
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* the interrupt disable state prior to the trap), the code segment register,
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* and the return instruction pointer are pushed by the cpu. The cpu
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* will also push an 'error' code for certain traps. We push a dummy
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* error code for those traps where the cpu doesn't in order to maintain
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* and the return instruction pointer are pushed by the cpu. The cpu
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* will also push an 'error' code for certain traps. We push a dummy
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* error code for those traps where the cpu doesn't in order to maintain
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* a consistent frame. We also push a contrived 'trap number'.
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*
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* The cpu does not push the general registers, we must do that, and we
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* The cpu does not push the general registers, we must do that, and we
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* must restore them prior to calling 'iret'. The cpu adjusts the %cs and
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* %ss segment registers, but does not mess with %ds, %es, or %fs. Thus we
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* must load them with appropriate values for supervisor mode operation.
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@ -145,13 +145,14 @@ IDTVEC(xmm)
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pushl $0; TRAP(T_XMMFLT)
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/*
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* alltraps entry point. Interrupts are enabled if this was a trap
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* gate (TGT), else disabled if this was an interrupt gate (IGT).
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* Note that int0x80_syscall is a trap gate. Interrupt gates are
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* used by page faults, non-maskable interrupts, debug and breakpoint
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* All traps except ones for syscalls jump to alltraps. If
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* interrupts were enabled when the trap occurred, then interrupts
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* are enabled now if the trap was through a trap gate, else
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* disabled if the trap was through an interrupt gate. Note that
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* int0x80_syscall is a trap gate. Interrupt gates are used by
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* page faults, non-maskable interrupts, debug and breakpoint
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* exceptions.
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*/
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SUPERALIGN_TEXT
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.globl alltraps
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.type alltraps,@function
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@ -168,7 +169,7 @@ calltrap:
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pushl %esp
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call trap
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add $4, %esp
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/*
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* Return via doreti to handle ASTs.
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*/
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@ -187,10 +188,10 @@ IDTVEC(ill)
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/* Check if this is a user fault. */
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cmpl $GSEL_KPL, 4(%esp) /* Check the code segment. */
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/* If so, just handle it as a normal trap. */
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jne norm_ill
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/*
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* This is a kernel instruction fault that might have been caused
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* by a DTrace provider.
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@ -215,10 +216,10 @@ norm_ill:
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#endif
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/*
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* SYSCALL CALL GATE (old entry point for a.out binaries)
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* Call gate entry for syscalls (lcall 7,0).
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* This is used by FreeBSD 1.x a.out executables and "old" NetBSD executables.
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*
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* The intersegment call has been set up to specify one dummy parameter.
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*
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* This leaves a place to put eflags so that the call frame can be
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* converted to a trap frame. Note that the eflags is (semi-)bogusly
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* pushed into (what will be) tf_err and then copied later into the
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@ -246,11 +247,13 @@ IDTVEC(lcall_syscall)
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jmp doreti
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/*
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* Call gate entry for FreeBSD ELF and Linux/NetBSD syscall (int 0x80)
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* Trap gate entry for syscalls (int 0x80).
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* This is used by FreeBSD ELF executables, "new" NetBSD executables, and all
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* Linux executables.
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*
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* Even though the name says 'int0x80', this is actually a TGT (trap gate)
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* rather then an IGT (interrupt gate). Thus interrupts are enabled on
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* entry just as they are for a normal syscall.
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* Even though the name says 'int0x80', this is actually a trap gate, not an
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* interrupt gate. Thus interrupts are enabled on entry just as they are for
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* a normal syscall.
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*/
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SUPERALIGN_TEXT
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IDTVEC(int0x80_syscall)
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@ -348,13 +351,14 @@ doreti_next:
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/*
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* PSL_VM must be checked first since segment registers only
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* have an RPL in non-VM86 mode.
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* ASTs can not be handled now if we are in a vm86 call.
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*/
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testl $PSL_VM,TF_EFLAGS(%esp) /* are we in vm86 mode? */
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testl $PSL_VM,TF_EFLAGS(%esp)
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jz doreti_notvm86
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movl PCPU(CURPCB),%ecx
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testl $PCB_VM86CALL,PCB_FLAGS(%ecx) /* are we in a vm86 call? */
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jz doreti_ast /* can handle ASTS now if not */
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jmp doreti_exit
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testl $PCB_VM86CALL,PCB_FLAGS(%ecx)
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jz doreti_ast
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jmp doreti_exit
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doreti_notvm86:
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testb $SEL_RPL_MASK,TF_CS(%esp) /* are we returning to user mode? */
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@ -401,7 +405,7 @@ doreti_popl_ds:
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doreti_iret:
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iret
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/*
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/*
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* doreti_iret_fault and friends. Alternative return code for
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* the case where we get a fault in the doreti_exit code
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* above. trap() (i386/i386/trap.c) catches this specific
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