svn commit: r251988 - in head/sys: amd64/amd64 i386/i386
Konstantin Belousov
kib at FreeBSD.org
Wed Jun 19 05:05:17 UTC 2013
Author: kib
Date: Wed Jun 19 05:05:16 2013
New Revision: 251988
URL: http://svnweb.freebsd.org/changeset/base/251988
Log:
Some clarifications and updates for the comments, mostly retrieved
from Bruce Evans. Trim the trailing spaces.
MFC after: 1 week
Modified:
head/sys/amd64/amd64/exception.S
head/sys/i386/i386/exception.s
Modified: head/sys/amd64/amd64/exception.S
==============================================================================
--- head/sys/amd64/amd64/exception.S Wed Jun 19 05:02:25 2013 (r251987)
+++ head/sys/amd64/amd64/exception.S Wed Jun 19 05:05:16 2013 (r251988)
@@ -80,18 +80,22 @@ dtrace_invop_calltrap_addr:
* This is equivalent to the i386 port's use of SDT_SYS386TGT.
*
* The cpu will push a certain amount of state onto the kernel stack for
- * the current process. See amd64/include/frame.h.
- * This includes the current RFLAGS (status register, which includes
+ * the current process. See amd64/include/frame.h.
+ * This includes the current RFLAGS (status register, which includes
* the interrupt disable state prior to the trap), the code segment register,
- * and the return instruction pointer are pushed by the cpu. The cpu
- * will also push an 'error' code for certain traps. We push a dummy
- * error code for those traps where the cpu doesn't in order to maintain
+ * and the return instruction pointer are pushed by the cpu. The cpu
+ * will also push an 'error' code for certain traps. We push a dummy
+ * error code for those traps where the cpu doesn't in order to maintain
* a consistent frame. We also push a contrived 'trap number'.
*
- * The cpu does not push the general registers, we must do that, and we
- * must restore them prior to calling 'iret'. The cpu adjusts the %cs and
- * %ss segment registers, but does not mess with %ds, %es, or %fs. Thus we
- * must load them with appropriate values for supervisor mode operation.
+ * The CPU does not push the general registers, so we must do that, and we
+ * must restore them prior to calling 'iret'. The CPU adjusts %cs and %ss
+ * but does not mess with %ds, %es, %gs or %fs. We swap the %gs base for
+ * for the kernel mode operation shortly, without changes to the selector
+ * loaded. Since superuser long mode works with any selectors loaded into
+ * segment registers other then %cs, which makes them mostly unused in long
+ * mode, and kernel does not reference %fs, leave them alone. The segment
+ * registers are reloaded on return to the usermode.
*/
MCOUNT_LABEL(user)
@@ -503,7 +507,7 @@ nmi_calltrap:
#ifdef HWPMC_HOOKS
/*
* Capture a userspace callchain if needed.
- *
+ *
* - Check if the current trap was from user mode.
* - Check if the current thread is valid.
* - Check if the thread requires a user call chain to be
@@ -549,7 +553,7 @@ outofnmi:
* At this point the processor has exited NMI mode and is running
* with interrupts turned off on the normal kernel stack.
*
- * If a pending NMI gets recognized at or after this point, it
+ * If a pending NMI gets recognized at or after this point, it
* will cause a kernel callchain to be traced.
*
* We turn interrupts back on, and call the user callchain capture hook.
@@ -567,7 +571,7 @@ nocallchain:
#endif
testl %ebx,%ebx
jnz doreti_exit
-nmi_kernelexit:
+nmi_kernelexit:
/*
* Put back the preserved MSR_GSBASE value.
*/
Modified: head/sys/i386/i386/exception.s
==============================================================================
--- head/sys/i386/i386/exception.s Wed Jun 19 05:02:25 2013 (r251987)
+++ head/sys/i386/i386/exception.s Wed Jun 19 05:05:16 2013 (r251988)
@@ -54,13 +54,13 @@
.globl dtrace_invop_jump_addr
.align 4
.type dtrace_invop_jump_addr, @object
- .size dtrace_invop_jump_addr, 4
+ .size dtrace_invop_jump_addr, 4
dtrace_invop_jump_addr:
.zero 4
.globl dtrace_invop_calltrap_addr
.align 4
.type dtrace_invop_calltrap_addr, @object
- .size dtrace_invop_calltrap_addr, 4
+ .size dtrace_invop_calltrap_addr, 4
dtrace_invop_calltrap_addr:
.zero 8
#endif
@@ -75,22 +75,22 @@ dtrace_invop_calltrap_addr:
* Trap and fault vector routines.
*
* Most traps are 'trap gates', SDT_SYS386TGT. A trap gate pushes state on
- * the stack that mostly looks like an interrupt, but does not disable
- * interrupts. A few of the traps we are use are interrupt gates,
+ * the stack that mostly looks like an interrupt, but does not disable
+ * interrupts. A few of the traps we are use are interrupt gates,
* SDT_SYS386IGT, which are nearly the same thing except interrupts are
* disabled on entry.
*
* The cpu will push a certain amount of state onto the kernel stack for
- * the current process. The amount of state depends on the type of trap
- * and whether the trap crossed rings or not. See i386/include/frame.h.
- * At the very least the current EFLAGS (status register, which includes
+ * the current process. The amount of state depends on the type of trap
+ * and whether the trap crossed rings or not. See i386/include/frame.h.
+ * At the very least the current EFLAGS (status register, which includes
* the interrupt disable state prior to the trap), the code segment register,
- * and the return instruction pointer are pushed by the cpu. The cpu
- * will also push an 'error' code for certain traps. We push a dummy
- * error code for those traps where the cpu doesn't in order to maintain
+ * and the return instruction pointer are pushed by the cpu. The cpu
+ * will also push an 'error' code for certain traps. We push a dummy
+ * error code for those traps where the cpu doesn't in order to maintain
* a consistent frame. We also push a contrived 'trap number'.
*
- * The cpu does not push the general registers, we must do that, and we
+ * The cpu does not push the general registers, we must do that, and we
* must restore them prior to calling 'iret'. The cpu adjusts the %cs and
* %ss segment registers, but does not mess with %ds, %es, or %fs. Thus we
* must load them with appropriate values for supervisor mode operation.
@@ -145,13 +145,14 @@ IDTVEC(xmm)
pushl $0; TRAP(T_XMMFLT)
/*
- * alltraps entry point. Interrupts are enabled if this was a trap
- * gate (TGT), else disabled if this was an interrupt gate (IGT).
- * Note that int0x80_syscall is a trap gate. Interrupt gates are
- * used by page faults, non-maskable interrupts, debug and breakpoint
+ * All traps except ones for syscalls jump to alltraps. If
+ * interrupts were enabled when the trap occurred, then interrupts
+ * are enabled now if the trap was through a trap gate, else
+ * disabled if the trap was through an interrupt gate. Note that
+ * int0x80_syscall is a trap gate. Interrupt gates are used by
+ * page faults, non-maskable interrupts, debug and breakpoint
* exceptions.
*/
-
SUPERALIGN_TEXT
.globl alltraps
.type alltraps, at function
@@ -168,7 +169,7 @@ calltrap:
pushl %esp
call trap
add $4, %esp
-
+
/*
* Return via doreti to handle ASTs.
*/
@@ -187,10 +188,10 @@ IDTVEC(ill)
/* Check if this is a user fault. */
cmpl $GSEL_KPL, 4(%esp) /* Check the code segment. */
-
+
/* If so, just handle it as a normal trap. */
jne norm_ill
-
+
/*
* This is a kernel instruction fault that might have been caused
* by a DTrace provider.
@@ -215,10 +216,10 @@ norm_ill:
#endif
/*
- * SYSCALL CALL GATE (old entry point for a.out binaries)
+ * Call gate entry for syscalls (lcall 7,0).
+ * This is used by FreeBSD 1.x a.out executables and "old" NetBSD executables.
*
* The intersegment call has been set up to specify one dummy parameter.
- *
* This leaves a place to put eflags so that the call frame can be
* converted to a trap frame. Note that the eflags is (semi-)bogusly
* pushed into (what will be) tf_err and then copied later into the
@@ -246,11 +247,13 @@ IDTVEC(lcall_syscall)
jmp doreti
/*
- * Call gate entry for FreeBSD ELF and Linux/NetBSD syscall (int 0x80)
+ * Trap gate entry for syscalls (int 0x80).
+ * This is used by FreeBSD ELF executables, "new" NetBSD executables, and all
+ * Linux executables.
*
- * Even though the name says 'int0x80', this is actually a TGT (trap gate)
- * rather then an IGT (interrupt gate). Thus interrupts are enabled on
- * entry just as they are for a normal syscall.
+ * Even though the name says 'int0x80', this is actually a trap gate, not an
+ * interrupt gate. Thus interrupts are enabled on entry just as they are for
+ * a normal syscall.
*/
SUPERALIGN_TEXT
IDTVEC(int0x80_syscall)
@@ -348,13 +351,14 @@ doreti_next:
/*
* PSL_VM must be checked first since segment registers only
* have an RPL in non-VM86 mode.
+ * ASTs can not be handled now if we are in a vm86 call.
*/
- testl $PSL_VM,TF_EFLAGS(%esp) /* are we in vm86 mode? */
+ testl $PSL_VM,TF_EFLAGS(%esp)
jz doreti_notvm86
movl PCPU(CURPCB),%ecx
- testl $PCB_VM86CALL,PCB_FLAGS(%ecx) /* are we in a vm86 call? */
- jz doreti_ast /* can handle ASTS now if not */
- jmp doreti_exit
+ testl $PCB_VM86CALL,PCB_FLAGS(%ecx)
+ jz doreti_ast
+ jmp doreti_exit
doreti_notvm86:
testb $SEL_RPL_MASK,TF_CS(%esp) /* are we returning to user mode? */
@@ -401,7 +405,7 @@ doreti_popl_ds:
doreti_iret:
iret
- /*
+ /*
* doreti_iret_fault and friends. Alternative return code for
* the case where we get a fault in the doreti_exit code
* above. trap() (i386/i386/trap.c) catches this specific
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