.altrp b6
.body
/*
- * We get here for syscalls that don't have a lightweight handler. For those, we
- * need to bubble down into the kernel and that requires setting up a minimal
- * pt_regs structure, and initializing the CPU state more or less as if an
- * interruption had occurred. To make syscall-restarts work, we setup pt_regs
- * such that cr_iip points to the second instruction in syscall_via_break.
- * Decrementing the IP hence will restart the syscall via break and not
- * decrementing IP will return us to the caller, as usual. Note that we preserve
- * the value of psr.pp rather than initializing it from dcr.pp. This makes it
- * possible to distinguish fsyscall execution from other privileged execution.
+ * We get here for syscalls that don't have a lightweight
+ * handler. For those, we need to bubble down into the kernel
+ * and that requires setting up a minimal pt_regs structure,
+ * and initializing the CPU state more or less as if an
+ * interruption had occurred. To make syscall-restarts work,
+ * we setup pt_regs such that cr_iip points to the second
+ * instruction in syscall_via_break. Decrementing the IP
+ * hence will restart the syscall via break and not
+ * decrementing IP will return us to the caller, as usual.
+ * Note that we preserve the value of psr.pp rather than
+ * initializing it from dcr.pp. This makes it possible to
+ * distinguish fsyscall execution from other privileged
+ * execution.
*
* On entry:
- * - normal fsyscall handler register usage, except that we also have:
+ * - normal fsyscall handler register usage, except
+ * that we also have:
* - r18: address of syscall entry point
* - r21: ar.fpsr
* - r26: ar.pfs
* - r27: ar.rsc
* - r29: psr
+ *
+ * We used to clear some PSR bits here but that requires slow
+ * serialization. Fortuntely, that isn't really necessary.
+ * The rationale is as follows: we used to clear bits
+ * ~PSR_PRESERVED_BITS in PSR.L. Since
+ * PSR_PRESERVED_BITS==PSR.{UP,MFL,MFH,PK,DT,PP,SP,RT,IC}, we
+ * ended up clearing PSR.{BE,AC,I,DFL,DFH,DI,DB,SI,TB}.
+ * However,
+ *
+ * PSR.BE : already is turned off in __kernel_syscall_via_epc()
+ * PSR.AC : don't care (kernel normally turns PSR.AC on)
+ * PSR.I : already turned off by the time fsys_bubble_down gets
+ * invoked
+ * PSR.DFL: always 0 (kernel never turns it on)
+ * PSR.DFH: don't care --- kernel never touches f32-f127 on its own
+ * initiative
+ * PSR.DI : always 0 (kernel never turns it on)
+ * PSR.SI : always 0 (kernel never turns it on)
+ * PSR.DB : don't care --- kernel never enables kernel-level
+ * breakpoints
+ * PSR.TB : must be 0 already; if it wasn't zero on entry to
+ * __kernel_syscall_via_epc, the branch to fsys_bubble_down
+ * will trigger a taken branch; the taken-trap-handler then
+ * converts the syscall into a break-based system-call.
*/
/*
- * Reading psr.l gives us only bits 0-31, psr.it, and psr.mc. The rest we have
- * to synthesize.
+ * Reading psr.l gives us only bits 0-31, psr.it, and psr.mc.
+ * The rest we have to synthesize.
*/
-# define PSR_ONE_BITS ((3 << IA64_PSR_CPL0_BIT) | (0x1 << IA64_PSR_RI_BIT) \
+# define PSR_ONE_BITS ((3 << IA64_PSR_CPL0_BIT) \
+ | (0x1 << IA64_PSR_RI_BIT) \
| IA64_PSR_BN | IA64_PSR_I)
- invala
- movl r14=ia64_ret_from_syscall
+ invala // M0|1
+ movl r14=ia64_ret_from_syscall // X
nop.m 0
- movl r28=__kernel_syscall_via_break
+ movl r28=__kernel_syscall_via_break // X create cr.iip
;;
- mov r2=r16 // copy current task addr to addl-addressable register
- adds r16=IA64_TASK_THREAD_ON_USTACK_OFFSET,r16
- mov r31=pr // save pr (2 cyc)
+ mov r2=r16 // A get task addr to addl-addressable register
+ adds r16=IA64_TASK_THREAD_ON_USTACK_OFFSET,r16 // A
+ mov r31=pr // I0 save pr (2 cyc)
;;
- st1 [r16]=r0 // clear current->thread.on_ustack flag
- addl r22=IA64_RBS_OFFSET,r2 // compute base of RBS
- add r3=TI_FLAGS+IA64_TASK_SIZE,r2
+ st1 [r16]=r0 // M2|3 clear current->thread.on_ustack flag
+ addl r22=IA64_RBS_OFFSET,r2 // A compute base of RBS
+ add r3=TI_FLAGS+IA64_TASK_SIZE,r2 // A
;;
- ld4 r3=[r3] // r2 = current_thread_info()->flags
- lfetch.fault.excl.nt1 [r22]
+ ld4 r3=[r3] // M0|1 r3 = current_thread_info()->flags
+ lfetch.fault.excl.nt1 [r22] // M0|1 prefetch register backing-store
nop.i 0
;;
- mov ar.rsc=0 // set enforced lazy mode, pl 0, little-endian, loadrs=0
+ mov ar.rsc=0 // M2 set enforced lazy mode, pl 0, LE, loadrs=0
nop.m 0
nop.i 0
;;
- mov r23=ar.bspstore // save ar.bspstore (12 cyc)
- mov.m r24=ar.rnat // read ar.rnat (5 cyc lat)
+ mov r23=ar.bspstore // M2 (12 cyc) save ar.bspstore
+ mov.m r24=ar.rnat // M2 (5 cyc) read ar.rnat (dual-issues!)
nop.i 0
;;
- mov ar.bspstore=r22 // switch to kernel RBS
+ mov ar.bspstore=r22 // M2 (6 cyc) switch to kernel RBS
movl r8=PSR_ONE_BITS // X
;;
- mov r25=ar.unat // save ar.unat (5 cyc)
- mov r19=b6 // save b6 (2 cyc)
- mov r20=r1 // save caller's gp in r20
+ mov r25=ar.unat // M2 (5 cyc) save ar.unat
+ mov r19=b6 // I0 save b6 (2 cyc)
+ mov r20=r1 // A save caller's gp in r20
;;
- or r29=r8,r29 // construct cr.ipsr value to save
- mov b6=r18 // copy syscall entry-point to b6 (7 cyc)
- addl r1=IA64_STK_OFFSET-IA64_PT_REGS_SIZE,r2 // compute base of memory stack
+ or r29=r8,r29 // A construct cr.ipsr value to save
+ mov b6=r18 // I0 copy syscall entry-point to b6 (7 cyc)
+ addl r1=IA64_STK_OFFSET-IA64_PT_REGS_SIZE,r2 // A compute base of memory stack
- mov r18=ar.bsp // save (kernel) ar.bsp (12 cyc)
- cmp.ne pKStk,pUStk=r0,r0 // set pKStk <- 0, pUStk <- 1
- br.call.sptk.many b7=ia64_syscall_setup
+ mov r18=ar.bsp // M2 save (kernel) ar.bsp (12 cyc)
+ cmp.ne pKStk,pUStk=r0,r0 // A set pKStk <- 0, pUStk <- 1
+ br.call.sptk.many b7=ia64_syscall_setup // B
;;
- mov ar.rsc=0x3 // set eager mode, pl 0, little-endian, loadrs=0
- mov rp=r14 // set the real return addr
+ mov ar.rsc=0x3 // M2 set eager mode, pl 0, LE, loadrs=0
+ mov rp=r14 // I0 set the real return addr
nop.i 0
;;
- ssm psr.i
- tbit.z p8,p0=r3,TIF_SYSCALL_TRACE
-(p10) br.cond.spnt.many ia64_ret_from_syscall // p10==true means out registers are more than 8
+ ssm psr.i // M2 we're on kernel stacks now, reenable irqs
+ tbit.z p8,p0=r3,TIF_SYSCALL_TRACE // I0
+(p10) br.cond.spnt.many ia64_ret_from_syscall // B return if bad call-frame or r15 is a NaT
nop.m 0
-(p8) br.call.sptk.many b6=b6 // ignore this return addr
- br.cond.spnt ia64_trace_syscall
+(p8) br.call.sptk.many b6=b6 // B (ignore return address)
+ br.cond.spnt ia64_trace_syscall // B
END(fsys_bubble_down)
.rodata
projects / linux-2.6 / commitdiff