56d20861c0
Call Frame Information is used by gdb for back-traces and inserting breakpoints on function return for the "finish" command. This failed when inside __kernel_clock_gettime. More concerning than difficulty debugging is that CFI is also used by stack frame unwinding code to implement exceptions. If you have an app that needs to handle asynchronous exceptions for some reason, and you are unlucky enough to get one inside the VDSO time functions, your app will crash. What's wrong: There is control flow in __kernel_clock_gettime that reaches label 99 without saving lr in r12. CFI info however is interpreted by the unwinder without reference to control flow: It's a simple matter of "Execute all the CFI opcodes up to the current address". That means the unwinder thinks r12 contains the return address at label 99. Disabuse it of that notion by resetting CFI for the return address at label 99. Note that the ".cfi_restore lr" could have gone anywhere from the "mtlr r12" a few instructions earlier to the instruction at label 99. I put the CFI as late as possible, because in general that's best practice (and if possible grouped with other CFI in order to reduce the number of CFI opcodes executed when unwinding). Using r12 as the return address is perfectly fine after the "mtlr r12" since r12 on that code path still contains the return address. __get_datapage also has a CFI error. That function temporarily saves lr in r0, and reflects that fact with ".cfi_register lr,r0". A later use of r0 means the CFI at that point isn't correct, as r0 no longer contains the return address. Fix that too. Signed-off-by: Alan Modra <amodra@gmail.com> Tested-by: Reza Arbab <arbab@linux.ibm.com> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
294 lines
6.8 KiB
ArmAsm
294 lines
6.8 KiB
ArmAsm
/*
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* Userland implementation of gettimeofday() for 32 bits processes in a
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* ppc64 kernel for use in the vDSO
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*
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* Copyright (C) 2004 Benjamin Herrenschmuidt (benh@kernel.crashing.org,
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* IBM Corp.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <asm/processor.h>
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#include <asm/ppc_asm.h>
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#include <asm/vdso.h>
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#include <asm/asm-offsets.h>
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#include <asm/unistd.h>
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/* Offset for the low 32-bit part of a field of long type */
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#ifdef CONFIG_PPC64
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#define LOPART 4
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#define TSPEC_TV_SEC TSPC64_TV_SEC+LOPART
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#else
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#define LOPART 0
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#define TSPEC_TV_SEC TSPC32_TV_SEC
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#endif
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.text
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/*
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* Exact prototype of gettimeofday
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*
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* int __kernel_gettimeofday(struct timeval *tv, struct timezone *tz);
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*
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*/
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V_FUNCTION_BEGIN(__kernel_gettimeofday)
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.cfi_startproc
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mflr r12
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.cfi_register lr,r12
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mr r10,r3 /* r10 saves tv */
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mr r11,r4 /* r11 saves tz */
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bl __get_datapage@local /* get data page */
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mr r9, r3 /* datapage ptr in r9 */
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cmplwi r10,0 /* check if tv is NULL */
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beq 3f
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lis r7,1000000@ha /* load up USEC_PER_SEC */
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addi r7,r7,1000000@l /* so we get microseconds in r4 */
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bl __do_get_tspec@local /* get sec/usec from tb & kernel */
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stw r3,TVAL32_TV_SEC(r10)
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stw r4,TVAL32_TV_USEC(r10)
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3: cmplwi r11,0 /* check if tz is NULL */
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beq 1f
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lwz r4,CFG_TZ_MINUTEWEST(r9)/* fill tz */
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lwz r5,CFG_TZ_DSTTIME(r9)
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stw r4,TZONE_TZ_MINWEST(r11)
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stw r5,TZONE_TZ_DSTTIME(r11)
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1: mtlr r12
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crclr cr0*4+so
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li r3,0
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blr
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.cfi_endproc
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V_FUNCTION_END(__kernel_gettimeofday)
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/*
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* Exact prototype of clock_gettime()
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*
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* int __kernel_clock_gettime(clockid_t clock_id, struct timespec *tp);
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*
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*/
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V_FUNCTION_BEGIN(__kernel_clock_gettime)
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.cfi_startproc
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/* Check for supported clock IDs */
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cmpli cr0,r3,CLOCK_REALTIME
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cmpli cr1,r3,CLOCK_MONOTONIC
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cror cr0*4+eq,cr0*4+eq,cr1*4+eq
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bne cr0,99f
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mflr r12 /* r12 saves lr */
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.cfi_register lr,r12
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mr r11,r4 /* r11 saves tp */
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bl __get_datapage@local /* get data page */
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mr r9,r3 /* datapage ptr in r9 */
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lis r7,NSEC_PER_SEC@h /* want nanoseconds */
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ori r7,r7,NSEC_PER_SEC@l
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50: bl __do_get_tspec@local /* get sec/nsec from tb & kernel */
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bne cr1,80f /* not monotonic -> all done */
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/*
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* CLOCK_MONOTONIC
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*/
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/* now we must fixup using wall to monotonic. We need to snapshot
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* that value and do the counter trick again. Fortunately, we still
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* have the counter value in r8 that was returned by __do_get_xsec.
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* At this point, r3,r4 contain our sec/nsec values, r5 and r6
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* can be used, r7 contains NSEC_PER_SEC.
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*/
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lwz r5,WTOM_CLOCK_SEC(r9)
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lwz r6,WTOM_CLOCK_NSEC(r9)
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/* We now have our offset in r5,r6. We create a fake dependency
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* on that value and re-check the counter
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*/
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or r0,r6,r5
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xor r0,r0,r0
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add r9,r9,r0
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lwz r0,(CFG_TB_UPDATE_COUNT+LOPART)(r9)
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cmpl cr0,r8,r0 /* check if updated */
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bne- 50b
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/* Calculate and store result. Note that this mimics the C code,
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* which may cause funny results if nsec goes negative... is that
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* possible at all ?
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*/
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add r3,r3,r5
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add r4,r4,r6
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cmpw cr0,r4,r7
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cmpwi cr1,r4,0
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blt 1f
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subf r4,r7,r4
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addi r3,r3,1
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1: bge cr1,80f
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addi r3,r3,-1
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add r4,r4,r7
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80: stw r3,TSPC32_TV_SEC(r11)
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stw r4,TSPC32_TV_NSEC(r11)
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mtlr r12
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crclr cr0*4+so
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li r3,0
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blr
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/*
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* syscall fallback
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*/
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99:
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li r0,__NR_clock_gettime
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.cfi_restore lr
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sc
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blr
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.cfi_endproc
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V_FUNCTION_END(__kernel_clock_gettime)
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/*
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* Exact prototype of clock_getres()
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*
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* int __kernel_clock_getres(clockid_t clock_id, struct timespec *res);
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*
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*/
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V_FUNCTION_BEGIN(__kernel_clock_getres)
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.cfi_startproc
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/* Check for supported clock IDs */
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cmpwi cr0,r3,CLOCK_REALTIME
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cmpwi cr1,r3,CLOCK_MONOTONIC
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cror cr0*4+eq,cr0*4+eq,cr1*4+eq
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bne cr0,99f
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li r3,0
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cmpli cr0,r4,0
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crclr cr0*4+so
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beqlr
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lis r5,CLOCK_REALTIME_RES@h
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ori r5,r5,CLOCK_REALTIME_RES@l
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stw r3,TSPC32_TV_SEC(r4)
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stw r5,TSPC32_TV_NSEC(r4)
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blr
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/*
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* syscall fallback
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*/
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99:
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li r0,__NR_clock_getres
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sc
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blr
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.cfi_endproc
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V_FUNCTION_END(__kernel_clock_getres)
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/*
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* Exact prototype of time()
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*
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* time_t time(time *t);
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*
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*/
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V_FUNCTION_BEGIN(__kernel_time)
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.cfi_startproc
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mflr r12
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.cfi_register lr,r12
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mr r11,r3 /* r11 holds t */
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bl __get_datapage@local
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mr r9, r3 /* datapage ptr in r9 */
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lwz r3,STAMP_XTIME+TSPEC_TV_SEC(r9)
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cmplwi r11,0 /* check if t is NULL */
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beq 2f
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stw r3,0(r11) /* store result at *t */
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2: mtlr r12
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crclr cr0*4+so
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blr
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.cfi_endproc
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V_FUNCTION_END(__kernel_time)
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/*
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* This is the core of clock_gettime() and gettimeofday(),
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* it returns the current time in r3 (seconds) and r4.
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* On entry, r7 gives the resolution of r4, either USEC_PER_SEC
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* or NSEC_PER_SEC, giving r4 in microseconds or nanoseconds.
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* It expects the datapage ptr in r9 and doesn't clobber it.
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* It clobbers r0, r5 and r6.
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* On return, r8 contains the counter value that can be reused.
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* This clobbers cr0 but not any other cr field.
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*/
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__do_get_tspec:
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.cfi_startproc
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/* Check for update count & load values. We use the low
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* order 32 bits of the update count
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*/
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1: lwz r8,(CFG_TB_UPDATE_COUNT+LOPART)(r9)
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andi. r0,r8,1 /* pending update ? loop */
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bne- 1b
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xor r0,r8,r8 /* create dependency */
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add r9,r9,r0
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/* Load orig stamp (offset to TB) */
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lwz r5,CFG_TB_ORIG_STAMP(r9)
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lwz r6,(CFG_TB_ORIG_STAMP+4)(r9)
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/* Get a stable TB value */
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2: MFTBU(r3)
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MFTBL(r4)
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MFTBU(r0)
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cmplw cr0,r3,r0
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bne- 2b
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/* Subtract tb orig stamp and shift left 12 bits.
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*/
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subfc r4,r6,r4
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subfe r0,r5,r3
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slwi r0,r0,12
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rlwimi. r0,r4,12,20,31
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slwi r4,r4,12
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/*
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* Load scale factor & do multiplication.
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* We only use the high 32 bits of the tb_to_xs value.
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* Even with a 1GHz timebase clock, the high 32 bits of
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* tb_to_xs will be at least 4 million, so the error from
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* ignoring the low 32 bits will be no more than 0.25ppm.
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* The error will just make the clock run very very slightly
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* slow until the next time the kernel updates the VDSO data,
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* at which point the clock will catch up to the kernel's value,
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* so there is no long-term error accumulation.
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*/
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lwz r5,CFG_TB_TO_XS(r9) /* load values */
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mulhwu r4,r4,r5
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li r3,0
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beq+ 4f /* skip high part computation if 0 */
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mulhwu r3,r0,r5
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mullw r5,r0,r5
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addc r4,r4,r5
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addze r3,r3
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4:
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/* At this point, we have seconds since the xtime stamp
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* as a 32.32 fixed-point number in r3 and r4.
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* Load & add the xtime stamp.
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*/
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lwz r5,STAMP_XTIME+TSPEC_TV_SEC(r9)
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lwz r6,STAMP_SEC_FRAC(r9)
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addc r4,r4,r6
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adde r3,r3,r5
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/* We create a fake dependency on the result in r3/r4
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* and re-check the counter
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*/
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or r6,r4,r3
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xor r0,r6,r6
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add r9,r9,r0
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lwz r0,(CFG_TB_UPDATE_COUNT+LOPART)(r9)
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cmplw cr0,r8,r0 /* check if updated */
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bne- 1b
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mulhwu r4,r4,r7 /* convert to micro or nanoseconds */
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blr
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.cfi_endproc
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