user/sven/linux.git/arch/arc/kernel/process.c, branch v3.18.74

ARC: Support syscall ABI v4

2016-09-01T02:05:44Z

[ Upstream commit 840c054fd0efb048df6fceb0c46385ec5b66dfe6 ] The syscall ABI includes the gcc functional calling ABI since a syscall implies userland caller and kernel callee. The current gcc ABI (v3) for ARCv2 ISA required 64-bit data be passed in even-odd register pairs, (potentially punching reg holes when passing such values as args). This was partly driven by the fact that the double-word LDD/STD instructions in ARCv2 expect the register alignment and thus gcc forcing this avoids extra MOV at the cost of a few unused register (which we have plenty anyways). This however was rejected as part of upstreaming gcc port to HS. So the new ABI v4 doesn't enforce the even-odd reg restriction. Do note that for ARCompact ISA builds v3 and v4 are practically the same in terms of gcc code generation. In terms of change management, we infer the new ABI if gcc 6.x onwards is used for building the kernel. This also needs a stable backport to enable older kernels to work with new tools/user-space Cc: Signed-off-by: Vineet Gupta Signed-off-by: Sasha Levin

ARC: make start_thread() out-of-line

2014-05-05T08:52:12Z

Helps move out ISA specific bits from a arch exported header Signed-off-by: Vineet Gupta

ARC: pt_regs update #5: Use real ECR for pt_regs->event vs. synth values

2013-06-26T08:34:48Z

pt_regs->event was set with artificial values to identify the low level system event (syscall trap / breakpoint trap / exceptions / interrupts) With r8 saving out of the way, the full word can be used to save real ECR (Exception Cause Register) which helps idenify the event naturally, including additional info such as cause code, param. Only for Interrupts, where ECR is not applicable, do we resort to synthetic non ECR values. SAVE_ALL_TRAP/EXCEPTIONS can now be merged as they both use ECR with different runtime values. The ptrace helpers now use the sub-fields of ECR to distinguish the events (e.g. vector 0x25 is trap, param 0 is syscall...) The following benefits will follow: (1) This centralizes the location of where ECR is saved and will allow the cleanup of task->thread.cause_code ECR placeholder which is set in non-uniform way. Then ARC VM code can safely rely on it being there for purpose of finer grained VM_EXEC dcache flush (based on exec fault: I-TLB Miss) (2) Further, ECR being passed around from low level handlers as arg can be eliminated as it is part of standard reg-file in pt_regs Signed-off-by: Vineet Gupta

ARC: pt_regs update #4: r25 saved/restored unconditionally

2013-06-22T13:53:25Z

(This is a VERY IMP change for low level interrupt/exception handling) ----------------------------------------------------------------------- WHAT ----------------------------------------------------------------------- * User 25 now saved in pt_regs->user_r25 (vs. tsk->thread_info.user_r25) * This allows Low level interrupt code to unconditionally save r25 (vs. the prev version which would only do it for U->K transition). Ofcourse for nested interrupts, only the pt_regs->user_r25 of bottom-most frame is useful. * simplifies the interrupt prologue/epilogue * Needed for ARCv2 ISA code and done here to keep design similar with ARCompact event handling ----------------------------------------------------------------------- WHY ------------------------------------------------------------------------- With CONFIG_ARC_CURR_IN_REG, r25 is used to cache "current" task pointer in kernel mode. So when entering kernel mode from User Mode - user r25 is specially safe-kept (it being a callee reg is NOT part of pt_regs which are saved by default on each interrupt/trap/exception) - r25 loaded with current task pointer. Further, if interrupt was taken in kernel mode, this is skipped since we know that r25 already has valid "current" pointer. With 2 level of interrupts in ARCompact ISA, detecting this is difficult but still possible, since we could be in kernel mode but r25 not already saved (in fact the stack itself might not have been switched). A. User mode B. L1 IRQ taken C. L2 IRQ taken (while on 1st line of L1 ISR) So in #C, although in kernel mode, r25 not saved (infact SP not switched at all) Given that ARcompact has manual stack switching, we could use a bit of trickey - The low level code would make sure that SP is only set to kernel mode value at the very end (after saving r25). So a non kernel mode SP, even if in kernel mode, meant r25 was NOT saved. The same paradigm won't work in ARCv2 ISA since SP is auto-switched so it's setting can't be delayed/constrained. Signed-off-by: Vineet Gupta

ARC: Increase readability of entry handlers

2013-06-22T13:53:23Z

* use artificial PUSH/POP contructs for CORE Reg save/restore to stack * use artificial PUSHAX/POPAX contructs for Auxiliary Space regs * macro'ize multiple copies of callee-reg-save/restore (SAVE_R13_TO_R24) * use BIC insn for inverse-and operation Signed-off-by: Vineet Gupta

ARC: pt_regs update #3: Remove unused gutter at start of callee_regs

2013-06-22T13:53:22Z

This is trickier than prev two: * context switching code saves kernel mode callee regs in the format of struct callee_regs thus needs adjustment. This also reduces the height of topmost kernel stack frame by 1 word. * Since kernel stack unwinder is sensitive to height of topmost kernel stack frame, that needs a word of adjustment too. ptrace needs a bit of updating since pt_regs now diverges from user_regs_struct. Signed-off-by: Vineet Gupta

ARC: pt_regs update #1: Align pt_regs end with end of kernel stack page

2013-06-22T13:53:21Z

Historically, pt_regs would end at offset of 1 word from end of stack page. ----------------- -> START of page (task->stack) | | | thread_info | ----------------- | | ^ ~ ~ | ~ ~ | | | | | | <---- pt_regs used to END here ----------------- | 1 word GUTTER | ----------------- -> End of page (START of kernel stack) This required special "one-off" considerations in low level code. The root cause is very likely assumption of "empty" SP by the original ARC kernel hackers, despite ARC700 always been "full" SP. So finally RIP one word gutter ! Signed-off-by: Vineet Gupta

arc: Use generic idle loop

2013-04-08T15:39:23Z

The generic idle loop implements all functionality. Aside of that it allows arc to implement the tsk_is_polling() functionality correctly, despite the patently (now gone) comment in the original arc cpu_idle() function: /* Since we SLEEP in idle loop, TIF_POLLING_NRFLAG can't be set */ See kernel/cpu/idle.c Signed-off-by: Thomas Gleixner Cc: Linus Torvalds Cc: Rusty Russell Cc: Paul McKenney Cc: Peter Zijlstra Reviewed-by: Cc: Srivatsa S. Bhat Cc: Magnus Damm Acked-by: Vineet Gupta Tested-by: Vineet Gupta Link: http://lkml.kernel.org/r/20130321215233.711253792@linutronix.de Signed-off-by: Thomas Gleixner

ARC: Fixup the current ABI version

2013-02-27T14:30:25Z

The upstream kernel ABI (v3) is different from current out-of-tree (v2): * no-legacy-syscalls * user_regs_struct layout has changed So we rev up the ABI version Signed-off-by: Vineet Gupta

ARC: Process-creation/scheduling/idle-loop

2013-02-11T14:30:38Z

Signed-off-by: Vineet Gupta Cc: Al Viro Cc: Thomas Gleixner