The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/i386/i386/swtch.s

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    1 /*-
    2  * Copyright (c) 1990 The Regents of the University of California.
    3  * All rights reserved.
    4  *
    5  * This code is derived from software contributed to Berkeley by
    6  * William Jolitz.
    7  *
    8  * Redistribution and use in source and binary forms, with or without
    9  * modification, are permitted provided that the following conditions
   10  * are met:
   11  * 1. Redistributions of source code must retain the above copyright
   12  *    notice, this list of conditions and the following disclaimer.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice, this list of conditions and the following disclaimer in the
   15  *    documentation and/or other materials provided with the distribution.
   16  * 3. Neither the name of the University nor the names of its contributors
   17  *    may be used to endorse or promote products derived from this software
   18  *    without specific prior written permission.
   19  *
   20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   30  * SUCH DAMAGE.
   31  *
   32  * $FreeBSD: head/sys/i386/i386/swtch.s 338313 2018-08-25 15:31:23Z kib $
   33  */
   34 
   35 #include "opt_sched.h"
   36 
   37 #include <machine/asmacros.h>
   38 
   39 #include "assym.inc"
   40 
   41 #if defined(SMP) && defined(SCHED_ULE)
   42 #define SETOP           xchgl
   43 #define BLOCK_SPIN(reg)                                                 \
   44                 movl            $blocked_lock,%eax ;                    \
   45         100: ;                                                          \
   46                 lock ;                                                  \
   47                 cmpxchgl        %eax,TD_LOCK(reg) ;                     \
   48                 jne             101f ;                                  \
   49                 pause ;                                                 \
   50                 jmp             100b ;                                  \
   51         101:
   52 #else
   53 #define SETOP           movl
   54 #define BLOCK_SPIN(reg)
   55 #endif
   56 
   57 /*****************************************************************************/
   58 /* Scheduling                                                                */
   59 /*****************************************************************************/
   60 
   61         .text
   62 
   63 /*
   64  * cpu_throw()
   65  *
   66  * This is the second half of cpu_switch(). It is used when the current
   67  * thread is either a dummy or slated to die, and we no longer care
   68  * about its state.  This is only a slight optimization and is probably
   69  * not worth it anymore.  Note that we need to clear the pm_active bits so
   70  * we do need the old proc if it still exists.
   71  * 0(%esp) = ret
   72  * 4(%esp) = oldtd
   73  * 8(%esp) = newtd
   74  */
   75 ENTRY(cpu_throw)
   76         movl    PCPU(CPUID), %esi
   77         /* release bit from old pm_active */
   78         movl    PCPU(CURPMAP), %ebx
   79 #ifdef SMP
   80         lock
   81 #endif
   82         btrl    %esi, PM_ACTIVE(%ebx)           /* clear old */
   83         movl    8(%esp),%ecx                    /* New thread */
   84         movl    TD_PCB(%ecx),%edx
   85         /* set bit in new pm_active */
   86         movl    TD_PROC(%ecx),%eax
   87         movl    P_VMSPACE(%eax), %ebx
   88         addl    $VM_PMAP, %ebx
   89         movl    %ebx, PCPU(CURPMAP)
   90 #ifdef SMP
   91         lock
   92 #endif
   93         btsl    %esi, PM_ACTIVE(%ebx)           /* set new */
   94         jmp     sw1
   95 END(cpu_throw)
   96 
   97 /*
   98  * cpu_switch(old, new)
   99  *
  100  * Save the current thread state, then select the next thread to run
  101  * and load its state.
  102  * 0(%esp) = ret
  103  * 4(%esp) = oldtd
  104  * 8(%esp) = newtd
  105  * 12(%esp) = newlock
  106  */
  107 ENTRY(cpu_switch)
  108 
  109         /* Switch to new thread.  First, save context. */
  110         movl    4(%esp),%ecx
  111 
  112 #ifdef INVARIANTS
  113         testl   %ecx,%ecx                       /* no thread? */
  114         jz      badsw2                          /* no, panic */
  115 #endif
  116 
  117         movl    TD_PCB(%ecx),%edx
  118 
  119         movl    (%esp),%eax                     /* Hardware registers */
  120         movl    %eax,PCB_EIP(%edx)
  121         movl    %ebx,PCB_EBX(%edx)
  122         movl    %esp,PCB_ESP(%edx)
  123         movl    %ebp,PCB_EBP(%edx)
  124         movl    %esi,PCB_ESI(%edx)
  125         movl    %edi,PCB_EDI(%edx)
  126         mov     %gs,PCB_GS(%edx)
  127         /* Test if debug registers should be saved. */
  128         testl   $PCB_DBREGS,PCB_FLAGS(%edx)
  129         jz      1f                              /* no, skip over */
  130         movl    %dr7,%eax                       /* yes, do the save */
  131         movl    %eax,PCB_DR7(%edx)
  132         andl    $0x0000fc00, %eax               /* disable all watchpoints */
  133         movl    %eax,%dr7
  134         movl    %dr6,%eax
  135         movl    %eax,PCB_DR6(%edx)
  136         movl    %dr3,%eax
  137         movl    %eax,PCB_DR3(%edx)
  138         movl    %dr2,%eax
  139         movl    %eax,PCB_DR2(%edx)
  140         movl    %dr1,%eax
  141         movl    %eax,PCB_DR1(%edx)
  142         movl    %dr0,%eax
  143         movl    %eax,PCB_DR0(%edx)
  144 1:
  145 
  146         /* have we used fp, and need a save? */
  147         cmpl    %ecx,PCPU(FPCURTHREAD)
  148         jne     1f
  149         pushl   PCB_SAVEFPU(%edx)               /* h/w bugs make saving complicated */
  150         call    npxsave                         /* do it in a big C function */
  151         popl    %eax
  152 1:
  153 
  154         /* Save is done.  Now fire up new thread. */
  155         movl    4(%esp),%edi
  156         movl    8(%esp),%ecx                    /* New thread */
  157         movl    12(%esp),%esi                   /* New lock */
  158 #ifdef INVARIANTS
  159         testl   %ecx,%ecx                       /* no thread? */
  160         jz      badsw3                          /* no, panic */
  161 #endif
  162         movl    TD_PCB(%ecx),%edx
  163 
  164         /* Switchout td_lock */
  165         movl    %esi,%eax
  166         movl    PCPU(CPUID),%esi
  167         SETOP   %eax,TD_LOCK(%edi)
  168 
  169         /* Release bit from old pmap->pm_active */
  170         movl    PCPU(CURPMAP), %ebx
  171 #ifdef SMP
  172         lock
  173 #endif
  174         btrl    %esi, PM_ACTIVE(%ebx)           /* clear old */
  175 
  176         /* Set bit in new pmap->pm_active */
  177         movl    TD_PROC(%ecx),%eax              /* newproc */
  178         movl    P_VMSPACE(%eax), %ebx
  179         addl    $VM_PMAP, %ebx
  180         movl    %ebx, PCPU(CURPMAP)
  181 #ifdef SMP
  182         lock
  183 #endif
  184         btsl    %esi, PM_ACTIVE(%ebx)           /* set new */
  185 sw1:
  186         BLOCK_SPIN(%ecx)
  187         /*
  188          * At this point, we have managed thread locks and are ready
  189          * to load up the rest of the next context.
  190          */
  191 
  192         /* Load a pointer to the thread kernel stack into PCPU. */
  193         leal    -VM86_STACK_SPACE(%edx), %eax   /* leave space for vm86 */
  194         movl    %eax, PCPU(KESP0)
  195 
  196         cmpl    $0, PCB_EXT(%edx)               /* has pcb extension? */
  197         je      1f                              /* If not, use the default */
  198         movl    $1, PCPU(PRIVATE_TSS)           /* mark use of private tss */
  199         movl    PCB_EXT(%edx), %edi             /* new tss descriptor */
  200         movl    PCPU(TRAMPSTK), %ebx
  201         movl    %ebx, PCB_EXT_TSS+TSS_ESP0(%edi)
  202         jmp     2f                              /* Load it up */
  203 
  204 1:      /*
  205          * Use the common default TSS instead of our own.
  206          * Stack pointer in the common TSS points to the trampoline stack
  207          * already and should be not changed.
  208          *
  209          * Test this CPU's flag to see if this CPU was using a private TSS.
  210          */
  211         cmpl    $0, PCPU(PRIVATE_TSS)           /* Already using the common? */
  212         je      3f                              /* if so, skip reloading */
  213         movl    $0, PCPU(PRIVATE_TSS)
  214         PCPU_ADDR(COMMON_TSSD, %edi)
  215 2:
  216         /* Move correct tss descriptor into GDT slot, then reload tr. */
  217         movl    PCPU(TSS_GDT), %ebx             /* entry in GDT */
  218         movl    0(%edi), %eax
  219         movl    4(%edi), %esi
  220         movl    %eax, 0(%ebx)
  221         movl    %esi, 4(%ebx)
  222         movl    $GPROC0_SEL*8, %esi             /* GSEL(GPROC0_SEL, SEL_KPL) */
  223         ltr     %si
  224 3:
  225 
  226         /* Copy the %fs and %gs selectors into this pcpu gdt */
  227         leal    PCB_FSD(%edx), %esi
  228         movl    PCPU(FSGS_GDT), %edi
  229         movl    0(%esi), %eax           /* %fs selector */
  230         movl    4(%esi), %ebx
  231         movl    %eax, 0(%edi)
  232         movl    %ebx, 4(%edi)
  233         movl    8(%esi), %eax           /* %gs selector, comes straight after */
  234         movl    12(%esi), %ebx
  235         movl    %eax, 8(%edi)
  236         movl    %ebx, 12(%edi)
  237 
  238         /* Restore context. */
  239         movl    PCB_EBX(%edx),%ebx
  240         movl    PCB_ESP(%edx),%esp
  241         movl    PCB_EBP(%edx),%ebp
  242         movl    PCB_ESI(%edx),%esi
  243         movl    PCB_EDI(%edx),%edi
  244         movl    PCB_EIP(%edx),%eax
  245         movl    %eax,(%esp)
  246 
  247         movl    %edx, PCPU(CURPCB)
  248         movl    %ecx, PCPU(CURTHREAD)           /* into next thread */
  249 
  250         /*
  251          * Determine the LDT to use and load it if is the default one and
  252          * that is not the current one.
  253          */
  254         movl    TD_PROC(%ecx),%eax
  255         cmpl    $0,P_MD+MD_LDT(%eax)
  256         jnz     1f
  257         movl    _default_ldt,%eax
  258         cmpl    PCPU(CURRENTLDT),%eax
  259         je      2f
  260         lldt    _default_ldt
  261         movl    %eax,PCPU(CURRENTLDT)
  262         jmp     2f
  263 1:
  264         /* Load the LDT when it is not the default one. */
  265         pushl   %edx                            /* Preserve pointer to pcb. */
  266         addl    $P_MD,%eax                      /* Pointer to mdproc is arg. */
  267         pushl   %eax
  268         /*
  269          * Holding dt_lock prevents context switches, so dt_lock cannot
  270          * be held now and set_user_ldt() will not deadlock acquiring it.
  271          */
  272         call    set_user_ldt
  273         addl    $4,%esp
  274         popl    %edx
  275 2:
  276 
  277         /* This must be done after loading the user LDT. */
  278         .globl  cpu_switch_load_gs
  279 cpu_switch_load_gs:
  280         mov     PCB_GS(%edx),%gs
  281 
  282         pushl   %edx
  283         pushl   PCPU(CURTHREAD)
  284         call    npxswitch
  285         popl    %edx
  286         popl    %edx
  287 
  288         /* Test if debug registers should be restored. */
  289         testl   $PCB_DBREGS,PCB_FLAGS(%edx)
  290         jz      1f
  291 
  292         /*
  293          * Restore debug registers.  The special code for dr7 is to
  294          * preserve the current values of its reserved bits.
  295          */
  296         movl    PCB_DR6(%edx),%eax
  297         movl    %eax,%dr6
  298         movl    PCB_DR3(%edx),%eax
  299         movl    %eax,%dr3
  300         movl    PCB_DR2(%edx),%eax
  301         movl    %eax,%dr2
  302         movl    PCB_DR1(%edx),%eax
  303         movl    %eax,%dr1
  304         movl    PCB_DR0(%edx),%eax
  305         movl    %eax,%dr0
  306         movl    %dr7,%eax
  307         andl    $0x0000fc00,%eax
  308         movl    PCB_DR7(%edx),%ecx
  309         andl    $~0x0000fc00,%ecx
  310         orl     %ecx,%eax
  311         movl    %eax,%dr7
  312 1:
  313         ret
  314 
  315 #ifdef INVARIANTS
  316 badsw1:
  317         pushal
  318         pushl   $sw0_1
  319         call    panic
  320 sw0_1:  .asciz  "cpu_throw: no newthread supplied"
  321 
  322 badsw2:
  323         pushal
  324         pushl   $sw0_2
  325         call    panic
  326 sw0_2:  .asciz  "cpu_switch: no curthread supplied"
  327 
  328 badsw3:
  329         pushal
  330         pushl   $sw0_3
  331         call    panic
  332 sw0_3:  .asciz  "cpu_switch: no newthread supplied"
  333 #endif
  334 END(cpu_switch)
  335 
  336 /*
  337  * savectx(pcb)
  338  * Update pcb, saving current processor state.
  339  */
  340 ENTRY(savectx)
  341         /* Fetch PCB. */
  342         movl    4(%esp),%ecx
  343 
  344         /* Save caller's return address.  Child won't execute this routine. */
  345         movl    (%esp),%eax
  346         movl    %eax,PCB_EIP(%ecx)
  347 
  348         movl    %cr3,%eax
  349         movl    %eax,PCB_CR3(%ecx)
  350 
  351         movl    %ebx,PCB_EBX(%ecx)
  352         movl    %esp,PCB_ESP(%ecx)
  353         movl    %ebp,PCB_EBP(%ecx)
  354         movl    %esi,PCB_ESI(%ecx)
  355         movl    %edi,PCB_EDI(%ecx)
  356         mov     %gs,PCB_GS(%ecx)
  357 
  358         movl    %cr0,%eax
  359         movl    %eax,PCB_CR0(%ecx)
  360         movl    %cr2,%eax
  361         movl    %eax,PCB_CR2(%ecx)
  362         movl    %cr4,%eax
  363         movl    %eax,PCB_CR4(%ecx)
  364 
  365         movl    %dr0,%eax
  366         movl    %eax,PCB_DR0(%ecx)
  367         movl    %dr1,%eax
  368         movl    %eax,PCB_DR1(%ecx)
  369         movl    %dr2,%eax
  370         movl    %eax,PCB_DR2(%ecx)
  371         movl    %dr3,%eax
  372         movl    %eax,PCB_DR3(%ecx)
  373         movl    %dr6,%eax
  374         movl    %eax,PCB_DR6(%ecx)
  375         movl    %dr7,%eax
  376         movl    %eax,PCB_DR7(%ecx)
  377 
  378         mov     %ds,PCB_DS(%ecx)
  379         mov     %es,PCB_ES(%ecx)
  380         mov     %fs,PCB_FS(%ecx)
  381         mov     %ss,PCB_SS(%ecx)
  382         
  383         sgdt    PCB_GDT(%ecx)
  384         sidt    PCB_IDT(%ecx)
  385         sldt    PCB_LDT(%ecx)
  386         str     PCB_TR(%ecx)
  387 
  388         movl    $1,%eax
  389         ret
  390 END(savectx)
  391 
  392 /*
  393  * resumectx(pcb) __fastcall
  394  * Resuming processor state from pcb.
  395  */
  396 ENTRY(resumectx)
  397         /* Restore GDT. */
  398         lgdt    PCB_GDT(%ecx)
  399 
  400         /* Restore segment registers */
  401         movzwl  PCB_DS(%ecx),%eax
  402         mov     %ax,%ds
  403         movzwl  PCB_ES(%ecx),%eax
  404         mov     %ax,%es
  405         movzwl  PCB_FS(%ecx),%eax
  406         mov     %ax,%fs
  407         movzwl  PCB_GS(%ecx),%eax
  408         movw    %ax,%gs
  409         movzwl  PCB_SS(%ecx),%eax
  410         mov     %ax,%ss
  411 
  412         /* Restore CR2, CR4, CR3 and CR0 */
  413         movl    PCB_CR2(%ecx),%eax
  414         movl    %eax,%cr2
  415         movl    PCB_CR4(%ecx),%eax
  416         movl    %eax,%cr4
  417         movl    PCB_CR3(%ecx),%eax
  418         movl    %eax,%cr3
  419         movl    PCB_CR0(%ecx),%eax
  420         movl    %eax,%cr0
  421         jmp     1f
  422 1:
  423 
  424         /* Restore descriptor tables */
  425         lidt    PCB_IDT(%ecx)
  426         lldt    PCB_LDT(%ecx)
  427 
  428 #define SDT_SYS386TSS   9
  429 #define SDT_SYS386BSY   11
  430         /* Clear "task busy" bit and reload TR */
  431         movl    PCPU(TSS_GDT),%eax
  432         andb    $(~SDT_SYS386BSY | SDT_SYS386TSS),5(%eax)
  433         movzwl  PCB_TR(%ecx),%eax
  434         ltr     %ax
  435 #undef SDT_SYS386TSS
  436 #undef SDT_SYS386BSY
  437 
  438         /* Restore debug registers */
  439         movl    PCB_DR0(%ecx),%eax
  440         movl    %eax,%dr0
  441         movl    PCB_DR1(%ecx),%eax
  442         movl    %eax,%dr1
  443         movl    PCB_DR2(%ecx),%eax
  444         movl    %eax,%dr2
  445         movl    PCB_DR3(%ecx),%eax
  446         movl    %eax,%dr3
  447         movl    PCB_DR6(%ecx),%eax
  448         movl    %eax,%dr6
  449         movl    PCB_DR7(%ecx),%eax
  450         movl    %eax,%dr7
  451 
  452         /* Restore other registers */
  453         movl    PCB_EDI(%ecx),%edi
  454         movl    PCB_ESI(%ecx),%esi
  455         movl    PCB_EBP(%ecx),%ebp
  456         movl    PCB_ESP(%ecx),%esp
  457         movl    PCB_EBX(%ecx),%ebx
  458 
  459         /* reload code selector by turning return into intersegmental return */
  460         pushl   PCB_EIP(%ecx)
  461         movl    $KCSEL,4(%esp)
  462         xorl    %eax,%eax
  463         lret
  464 END(resumectx)

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