On Wed, Aug 5, 2009 at 3:47 AM, Ouyang Jiannan <jallen....@gmail.com> wrote:
> Thanks > I've noticed that bionic uses address 0xffff0ff0 to implement TLS in arm > But isn't this address a space of kernel? How can a user space program > access that address without a soft-interupt... > > Or the memory map in arm is different from x86, so the high 1G mem is not > kernel used only? > I don't know the details, but I know it relies on a weird kernel tricks. Be it a special page fault, or a special page mapping. Actually, another similar address contains the address of a function to be called by user code to get the same TLS pointer. This is supposedly more portable (it is used by the ARMv4T port, if I remember correctly), but can also be slower. The ARMv6 way of using a dedicated register is supposed to get much better performance, but of course can't be used by NDK-generated binaries which are built for ARMv5TE. > > On Wed, Aug 5, 2009 at 3:06 AM, David Turner <di...@android.com> wrote: > >> >> >> On Tue, Aug 4, 2009 at 12:24 PM, Neo <zingafri...@yahoo.com> wrote: >> >>> >>> >>> >>> On Aug 4, 8:17 am, Ouyang Jiannan <jallen....@gmail.com> wrote: >>> > hi, everyone, >>> > In bionic/libc/Android.mk we can see that >>> > x86 uses files pthread.c, pthread-timers.c ptrace.c and __get_tls.c >>> > in arm, it uses pthread.c.arm , pthread-timers.c.arm, ptrace.c.arm >>> > But I can't find these files or places which generate it >>> > >>> > So what's the arm support of TLS? Is there a reg uses as gs in x86 as a >>> > pointer to tls? >>> >>> TLS is not supported in android though it is present in armv6 and >>> later. >> >> >> TLS is supported in Android (there wouldn't be any pthread implementation >> anyway). >> >> The current ARM implementation doesn't use an ARMv6-specific register but >> instead >> relies on a small kernel trick (which updates a very specific user virtual >> address on each >> context switch instead). >> >> >>> >>> >>> >> >> >> > > > > --~--~---------~--~----~------------~-------~--~----~ unsubscribe: android-porting+unsubscr...@googlegroups.com website: http://groups.google.com/group/android-porting -~----------~----~----~----~------~----~------~--~---
