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  • Nagarathnam Muthusamy's avatar
    vDSO for sparc · 9a08862a
    Nagarathnam Muthusamy authored
    
    
    Following patch is based on work done by Nick Alcock on 64-bit vDSO for sparc
    in Oracle linux. I have extended it to include support for 32-bit vDSO for sparc
    on 64-bit kernel.
    
    vDSO for sparc is based on the X86 implementation. This patch
    provides vDSO support for both 64-bit and 32-bit programs on 64-bit kernel.
    vDSO will be disabled on 32-bit linux kernel on sparc.
    
    *) vclock_gettime.c contains all the vdso functions. Since data page is mapped
       before the vdso code page, the pointer to data page is got by subracting offset
       from an address in the vdso code page. The return address stored in
       %i7 is used for this purpose.
    *) During compilation, both 32-bit and 64-bit vdso images are compiled and are
       converted into raw bytes by vdso2c program to be ready for mapping into the
       process. 32-bit images are compiled only if CONFIG_COMPAT is enabled. vdso2c
       generates two files vdso-image-64.c and vdso-image-32.c which contains the
       respective vDSO image in C structure.
    *) During vdso initialization, required number of vdso pages are allocated and
       raw bytes are copied into the pages.
    *) During every exec, these pages are mapped into the process through
       arch_setup_additional_pages and the location of mapping is passed on to the
       process through aux vector AT_SYSINFO_EHDR which is used by glibc.
    *) A new update_vsyscall routine for sparc is added to keep the data page in
       vdso updated.
    *) As vDSO cannot contain dynamically relocatable references, a new version of
       cpu_relax is added for the use of vDSO.
    
    This change also requires a putback to glibc to use vDSO. For testing,
    programs planning to try vDSO can be compiled against the generated
    vdso(64/32).so in the source.
    
    Testing:
    
    ========
    [root@localhost ~]# cat vdso_test.c
    int main() {
            struct timespec tv_start, tv_end;
            struct timeval tv_tmp;
    	int i;
            int count = 1 * 1000 * 10000;
    	long long diff;
    
            clock_gettime(0, &tv_start);
            for (i = 0; i < count; i++)
                  gettimeofday(&tv_tmp, NULL);
            clock_gettime(0, &tv_end);
            diff = (long long)(tv_end.tv_sec -
    		tv_start.tv_sec)*(1*1000*1000*1000);
            diff += (tv_end.tv_nsec - tv_start.tv_nsec);
    	printf("Start sec: %d\n", tv_start.tv_sec);
    	printf("End sec  : %d\n", tv_end.tv_sec);
            printf("%d cycles in %lld ns = %f ns/cycle\n", count, diff,
    		(double)diff / (double)count);
            return 0;
    }
    
    [root@localhost ~]# cc vdso_test.c -o t32_without_fix -m32 -lrt
    [root@localhost ~]# ./t32_without_fix
    Start sec: 1502396130
    End sec  : 1502396140
    10000000 cycles in 9565148528 ns = 956.514853 ns/cycle
    [root@localhost ~]# cc vdso_test.c -o t32_with_fix -m32 ./vdso32.so.dbg
    [root@localhost ~]# ./t32_with_fix
    Start sec: 1502396168
    End sec  : 1502396169
    10000000 cycles in 798141262 ns = 79.814126 ns/cycle
    [root@localhost ~]# cc vdso_test.c -o t64_without_fix -m64 -lrt
    [root@localhost ~]# ./t64_without_fix
    Start sec: 1502396208
    End sec  : 1502396218
    10000000 cycles in 9846091800 ns = 984.609180 ns/cycle
    [root@localhost ~]# cc vdso_test.c -o t64_with_fix -m64 ./vdso64.so.dbg
    [root@localhost ~]# ./t64_with_fix
    Start sec: 1502396257
    End sec  : 1502396257
    10000000 cycles in 380984048 ns = 38.098405 ns/cycle
    
    V1 to V2 Changes:
    =================
    	Added hot patching code to switch the read stick instruction to read
    tick instruction based on the hardware.
    
    V2 to V3 Changes:
    =================
    	Merged latest changes from sparc-next and moved the initialization
    of clocksource_tick.archdata.vclock_mode to time_init_early. Disabled
    queued spinlock and rwlock configuration when simulating 32-bit config
    to compile 32-bit VDSO.
    
    V3 to V4 Changes:
    =================
    	Hardcoded the page size as 8192 in linker script for both 64-bit and
    32-bit binaries. Removed unused variables in vdso2c.h. Added -mv8plus flag to
    Makefile to prevent the generation of relocation entries for __lshrdi3 in 32-bit
    vdso binary.
    
    Signed-off-by: default avatarNick Alcock <nick.alcock@oracle.com>
    Signed-off-by: default avatarNagarathnam Muthusamy <nagarathnam.muthusamy@oracle.com>
    Reviewed-by: default avatarShannon Nelson <shannon.nelson@oracle.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    9a08862a