/* * wof.S: Sparc window overflow handler. * * Copyright (C) 1995 David S. Miller (davem@caip.rutgers.edu) */ #include <asm/contregs.h> #include <asm/page.h> #include <asm/ptrace.h> #include <asm/psr.h> #include <asm/smp.h> #include <asm/asi.h> #include <asm/winmacro.h> #include <asm/asmmacro.h> #include <asm/thread_info.h> /* WARNING: This routine is hairy and _very_ complicated, but it * must be as fast as possible as it handles the allocation * of register windows to the user and kernel. If you touch * this code be _very_ careful as many other pieces of the * kernel depend upon how this code behaves. You have been * duly warned... */ /* We define macro's for registers which have a fixed * meaning throughout this entire routine. The 'T' in * the comments mean that the register can only be * accessed when in the 'trap' window, 'G' means * accessible in any window. Do not change these registers * after they have been set, until you are ready to return * from the trap. */ #define t_psr l0 /* %psr at trap time T */ #define t_pc l1 /* PC for trap return T */ #define t_npc l2 /* NPC for trap return T */ #define t_wim l3 /* %wim at trap time T */ #define saved_g5 l5 /* Global save register T */ #define saved_g6 l6 /* Global save register T */ #define curptr g6 /* Gets set to 'current' then stays G */ /* Now registers whose values can change within the handler. */ #define twin_tmp l4 /* Temp reg, only usable in trap window T */ #define glob_tmp g5 /* Global temporary reg, usable anywhere G */ .text .align 4 /* BEGINNING OF PATCH INSTRUCTIONS */ /* On a 7-window Sparc the boot code patches spnwin_* * instructions with the following ones. */ .globl spnwin_patch1_7win, spnwin_patch2_7win, spnwin_patch3_7win spnwin_patch1_7win: sll %t_wim, 6, %glob_tmp spnwin_patch2_7win: and %glob_tmp, 0x7f, %glob_tmp spnwin_patch3_7win: and %twin_tmp, 0x7f, %twin_tmp /* END OF PATCH INSTRUCTIONS */ /* The trap entry point has done the following: * * rd %psr, %l0 * rd %wim, %l3 * b spill_window_entry * andcc %l0, PSR_PS, %g0 */ /* Datum current_thread_info->uwinmask contains at all times a bitmask * where if any user windows are active, at least one bit will * be set in to mask. If no user windows are active, the bitmask * will be all zeroes. */ .globl spill_window_entry .globl spnwin_patch1, spnwin_patch2, spnwin_patch3 spill_window_entry: /* LOCATION: Trap Window */ mov %g5, %saved_g5 ! save away global temp register mov %g6, %saved_g6 ! save away 'current' ptr register /* Compute what the new %wim will be if we save the * window properly in this trap handler. * * newwim = ((%wim>>1) | (%wim<<(nwindows - 1))); */ srl %t_wim, 0x1, %twin_tmp spnwin_patch1: sll %t_wim, 7, %glob_tmp or %glob_tmp, %twin_tmp, %glob_tmp spnwin_patch2: and %glob_tmp, 0xff, %glob_tmp /* The trap entry point has set the condition codes * up for us to see if this is from user or kernel. * Get the load of 'curptr' out of the way. */ LOAD_CURRENT(curptr, twin_tmp) andcc %t_psr, PSR_PS, %g0 be,a spwin_fromuser ! all user wins, branch save %g0, %g0, %g0 ! Go where saving will occur /* See if any user windows are active in the set. */ ld [%curptr + TI_UWINMASK], %twin_tmp ! grab win mask orcc %g0, %twin_tmp, %g0 ! check for set bits bne spwin_exist_uwins ! yep, there are some andn %twin_tmp, %glob_tmp, %twin_tmp ! compute new uwinmask /* Save into the window which must be saved and do it. * Basically if we are here, this means that we trapped * from kernel mode with only kernel windows in the register * file. */ save %g0, %g0, %g0 ! save into the window to stash away wr %glob_tmp, 0x0, %wim ! set new %wim, this is safe now spwin_no_userwins_from_kernel: /* LOCATION: Window to be saved */ STORE_WINDOW(sp) ! stash the window restore %g0, %g0, %g0 ! go back into trap window /* LOCATION: Trap window */ mov %saved_g5, %g5 ! restore %glob_tmp mov %saved_g6, %g6 ! restore %curptr wr %t_psr, 0x0, %psr ! restore condition codes in %psr WRITE_PAUSE ! waste some time jmp %t_pc ! Return from trap rett %t_npc ! we are done spwin_exist_uwins: /* LOCATION: Trap window */ /* Wow, user windows have to be dealt with, this is dirty * and messy as all hell. And difficult to follow if you * are approaching the infamous register window trap handling * problem for the first time. DON'T LOOK! * * Note that how the execution path works out, the new %wim * will be left for us in the global temporary register, * %glob_tmp. We cannot set the new %wim first because we * need to save into the appropriate window without inducing * a trap (traps are off, we'd get a watchdog wheee)... * But first, store the new user window mask calculated * above. */ st %twin_tmp, [%curptr + TI_UWINMASK] save %g0, %g0, %g0 ! Go to where the saving will occur spwin_fromuser: /* LOCATION: Window to be saved */ wr %glob_tmp, 0x0, %wim ! Now it is safe to set new %wim /* LOCATION: Window to be saved */ /* This instruction branches to a routine which will check * to validity of the users stack pointer by whatever means * are necessary. This means that this is architecture * specific and thus this branch instruction will need to * be patched at boot time once the machine type is known. * This routine _shall not_ touch %curptr under any * circumstances whatsoever! It will branch back to the * label 'spwin_good_ustack' if the stack is ok but still * needs to be dumped (SRMMU for instance will not need to * do this) or 'spwin_finish_up' if the stack is ok and the * registers have already been saved. If the stack is found * to be bogus for some reason the routine shall branch to * the label 'spwin_user_stack_is_bolixed' which will take * care of things at that point. */ b spwin_srmmu_stackchk andcc %sp, 0x7, %g0 spwin_good_ustack: /* LOCATION: Window to be saved */ /* The users stack is ok and we can safely save it at * %sp. */ STORE_WINDOW(sp) spwin_finish_up: restore %g0, %g0, %g0 /* Back to trap window. */ /* LOCATION: Trap window */ /* We have spilled successfully, and we have properly stored * the appropriate window onto the stack. */ /* Restore saved globals */ mov %saved_g5, %g5 mov %saved_g6, %g6 wr %t_psr, 0x0, %psr WRITE_PAUSE jmp %t_pc rett %t_npc spwin_user_stack_is_bolixed: /* LOCATION: Window to be saved */ /* Wheee, user has trashed his/her stack. We have to decide * how to proceed based upon whether we came from kernel mode * or not. If we came from kernel mode, toss the window into * a special buffer and proceed, the kernel _needs_ a window * and we could be in an interrupt handler so timing is crucial. * If we came from user land we build a full stack frame and call * c-code to gun down the process. */ rd %psr, %glob_tmp andcc %glob_tmp, PSR_PS, %g0 bne spwin_bad_ustack_from_kernel nop /* Oh well, throw this one window into the per-task window * buffer, the first one. */ st %sp, [%curptr + TI_RWIN_SPTRS] STORE_WINDOW(curptr + TI_REG_WINDOW) restore %g0, %g0, %g0 /* LOCATION: Trap Window */ /* Back in the trap window, update winbuffer save count. */ mov 1, %twin_tmp st %twin_tmp, [%curptr + TI_W_SAVED] /* Compute new user window mask. What we are basically * doing is taking two windows, the invalid one at trap * time and the one we attempted to throw onto the users * stack, and saying that everything else is an ok user * window. umask = ((~(%t_wim | %wim)) & valid_wim_bits) */ rd %wim, %twin_tmp or %twin_tmp, %t_wim, %twin_tmp not %twin_tmp spnwin_patch3: and %twin_tmp, 0xff, %twin_tmp ! patched on 7win Sparcs st %twin_tmp, [%curptr + TI_UWINMASK] #define STACK_OFFSET (THREAD_SIZE - TRACEREG_SZ - STACKFRAME_SZ) sethi %hi(STACK_OFFSET), %sp or %sp, %lo(STACK_OFFSET), %sp add %curptr, %sp, %sp /* Restore the saved globals and build a pt_regs frame. */ mov %saved_g5, %g5 mov %saved_g6, %g6 STORE_PT_ALL(sp, t_psr, t_pc, t_npc, g1) sethi %hi(STACK_OFFSET), %g6 or %g6, %lo(STACK_OFFSET), %g6 sub %sp, %g6, %g6 ! curptr /* Turn on traps and call c-code to deal with it. */ wr %t_psr, PSR_ET, %psr nop call window_overflow_fault nop /* Return from trap if C-code actually fixes things, if it * doesn't then we never get this far as the process will * be given the look of death from Commander Peanut. */ b ret_trap_entry clr %l6 spwin_bad_ustack_from_kernel: /* LOCATION: Window to be saved */ /* The kernel provoked a spill window trap, but the window we * need to save is a user one and the process has trashed its * stack pointer. We need to be quick, so we throw it into * a per-process window buffer until we can properly handle * this later on. */ SAVE_BOLIXED_USER_STACK(curptr, glob_tmp) restore %g0, %g0, %g0 /* LOCATION: Trap window */ /* Restore globals, condition codes in the %psr and * return from trap. Note, restoring %g6 when returning * to kernel mode is not necessarily these days. ;-) */ mov %saved_g5, %g5 mov %saved_g6, %g6 wr %t_psr, 0x0, %psr WRITE_PAUSE jmp %t_pc rett %t_npc /* Undefine the register macros which would only cause trouble * if used below. This helps find 'stupid' coding errors that * produce 'odd' behavior. The routines below are allowed to * make usage of glob_tmp and t_psr so we leave them defined. */ #undef twin_tmp #undef curptr #undef t_pc #undef t_npc #undef t_wim #undef saved_g5 #undef saved_g6 /* Now come the per-architecture window overflow stack checking routines. * As noted above %curptr cannot be touched by this routine at all. */ /* This is a generic SRMMU routine. As far as I know this * works for all current v8/srmmu implementations, we'll * see... */ .globl spwin_srmmu_stackchk spwin_srmmu_stackchk: /* LOCATION: Window to be saved on the stack */ /* Because of SMP concerns and speed we play a trick. * We disable fault traps in the MMU control register, * Execute the stores, then check the fault registers * to see what happens. I can hear Linus now * "disgusting... broken hardware...". * * But first, check to see if the users stack has ended * up in kernel vma, then we would succeed for the 'wrong' * reason... ;( Note that the 'sethi' below assumes the * kernel is page aligned, which should always be the case. */ /* Check results of callers andcc %sp, 0x7, %g0 */ bne spwin_user_stack_is_bolixed sethi %hi(PAGE_OFFSET), %glob_tmp cmp %glob_tmp, %sp bleu spwin_user_stack_is_bolixed mov AC_M_SFSR, %glob_tmp /* Clear the fault status and turn on the no_fault bit. */ LEON_PI(lda [%glob_tmp] ASI_LEON_MMUREGS, %g0) ! eat SFSR SUN_PI_(lda [%glob_tmp] ASI_M_MMUREGS, %g0) ! eat SFSR LEON_PI(lda [%g0] ASI_LEON_MMUREGS, %glob_tmp) ! read MMU control SUN_PI_(lda [%g0] ASI_M_MMUREGS, %glob_tmp) ! read MMU control or %glob_tmp, 0x2, %glob_tmp ! or in no_fault bit LEON_PI(sta %glob_tmp, [%g0] ASI_LEON_MMUREGS) ! set it SUN_PI_(sta %glob_tmp, [%g0] ASI_M_MMUREGS) ! set it /* Dump the registers and cross fingers. */ STORE_WINDOW(sp) /* Clear the no_fault bit and check the status. */ andn %glob_tmp, 0x2, %glob_tmp LEON_PI(sta %glob_tmp, [%g0] ASI_LEON_MMUREGS) SUN_PI_(sta %glob_tmp, [%g0] ASI_M_MMUREGS) mov AC_M_SFAR, %glob_tmp LEON_PI(lda [%glob_tmp] ASI_LEON_MMUREGS, %g0) SUN_PI_(lda [%glob_tmp] ASI_M_MMUREGS, %g0) mov AC_M_SFSR, %glob_tmp LEON_PI(lda [%glob_tmp] ASI_LEON_MMUREGS, %glob_tmp) SUN_PI_(lda [%glob_tmp] ASI_M_MMUREGS, %glob_tmp) andcc %glob_tmp, 0x2, %g0 ! did we fault? be,a spwin_finish_up + 0x4 ! cool beans, success restore %g0, %g0, %g0 rd %psr, %glob_tmp b spwin_user_stack_is_bolixed + 0x4 ! we faulted, ugh nop