[RFC/PATCH v2] ARM: vDSO gettimeofday using generic timer architecture
Nathan Lynch
Nathan_Lynch at mentor.com
Mon Feb 10 18:57:19 EST 2014
On 02/09/2014 04:20 AM, Russell King - ARM Linux wrote:
> On Fri, Feb 07, 2014 at 05:05:49PM -0600, Nathan Lynch wrote:
>> + /* Grab the vDSO code pages. */
>> + for (i = 0; i < vdso_pages; i++) {
>> + pg = virt_to_page(&vdso_start + i*PAGE_SIZE);
>> + ClearPageReserved(pg);
>> + get_page(pg);
>> + vdso_pagelist[i] = pg;
>> + }
>
> Why do we want to clear the reserved status? This looks over complicated
> to me.
>
>> +
>> + /* Sanity check the shared object header. */
>> + vbase = vmap(vdso_pagelist, 1, 0, PAGE_KERNEL);
>> + if (vbase == NULL) {
>> + pr_err("Failed to map vDSO pagelist!\n");
>> + return -ENOMEM;
>> + } else if (memcmp(vbase, "\177ELF", 4)) {
>> + pr_err("vDSO is not a valid ELF object!\n");
>> + ret = -EINVAL;
>> + goto unmap;
>> + }
>
> Why do we need to vmap() pages which are already accessible - vdso_start
> must be part of the kernel image, and therefore will be accessible via
> standard mappings.
Right, this stuff doesn't appear to be necessary. Removed the vmap,
get_page, and ClearPageReserved calls for v3.
>> +static long clock_gettime_fallback(clockid_t _clkid, struct timespec *_ts)
>> +{
>> + register struct timespec *ts asm("r1") = _ts;
>> + register clockid_t clkid asm("r0") = _clkid;
>> + register long ret asm ("r0");
>> + register long nr asm("r7") = __NR_clock_gettime;
>> +
>> + asm("swi #0" : "=r" (ret) : "r" (clkid), "r" (ts), "r" (nr) : "memory");
>
> This isn't compatible with OABI, so either this must not be enabled when
> AEABI is disabled, or this needs to be fixed.
Okay. I'll plan on making the vdso code depend on CONFIG_AEABI, likely
indirectly via a CONFIG_VDSO Kconfig option. Since you'll need an
updated C library to actually benefit from the vdso, I doubt any OABI
support in this code would get any use.
Thanks for reviewing.
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