Sergey Bugaev, le dim. 12 févr. 2023 19:25:11 +0300, a ecrit: > On Sun, Feb 12, 2023 at 7:11 PM Samuel Thibault <samuel.thiba...@gnu.org> > wrote: > > Sergey Bugaev, le dim. 12 févr. 2023 14:10:42 +0300, a ecrit: > > > We should not need a getter routine, because one can simply inspect the > > > target > > > thread's state (unless, again, I misunderstand things horribly). > > > > For 16bit fs/gs values we could read them from userland yes. But for > > fs/gs base, the FSGSBASE instruction is not available on all 64bit > > processors. And ATM in THREAD_TCB we want to be able to get the base of > > another thread. > > What I've meant is: > > __thread_get_state (whatever_thread, &state); > uintptr_t its_fs_base = state->fs_base; > > You can't really do the same to *write* [fg]s_base, because doing > thread_set_state on your own thread is bound to end badly.
? Well, sure, just like setting fs/gs through thread state was not done for i386. I don't see where you're aiming. Getting fs/gs from __thread_get_state won't actually give you the base, you'll just read something like 0. > > > diff --git a/sysdeps/mach/hurd/x86_64/static-start.S > > > b/sysdeps/mach/hurd/x86_64/static-start.S > > > new file mode 100644 > > > index 00000000..982d3d52 > > > --- /dev/null > > > +++ b/sysdeps/mach/hurd/x86_64/static-start.S > > > @@ -0,0 +1,27 @@ > > > +/* Type of the TCB. */ > > > +typedef struct > > > +{ > > > + void *tcb; /* Points to this structure. */ > > > + dtv_t *dtv; /* Vector of pointers to TLS data. > > > */ > > > + thread_t self; /* This thread's control port. */ > > > + int __glibc_padding1; > > > + int multiple_threads; > > > + int gscope_flag; > > > + uintptr_t sysinfo; > > > + uintptr_t stack_guard; > > > + uintptr_t pointer_guard; > > > + long __glibc_padding2[2]; > > > + int private_futex; > > > > ? Isn't that rather feature_1 ? > > sysdeps/mach/hurd/i386/tls.h has 'int private_futex;', which is where > I stole this from. A quick grep confirms that it's never used, Yes, this was just to align on the nptl tls.h. But apparently that got renamed and hurd's tls wasn't updated. > so we might rename both to feature_1, or maybe another instance of > __glibc_padding. Better stay coherent with the nptl version. > > > +/* GCC generates %fs:0x28 to access the stack guard. */ > > > +_Static_assert (offsetof (tcbhead_t, stack_guard) == 0x28, > > > + "stack guard offset"); > > > +/* libgcc uses %fs:0x70 to access the split stack pointer. */ > > > +_Static_assert (offsetof (tcbhead_t, __private_ss) == 0x70, > > > + "split stack pointer offset"); > > > > Indeed. Could you perhaps also add them to the i386 tls.h? > > > > +/* Install new dtv for current thread. */ > > > +# define INSTALL_NEW_DTV(dtvp) THREAD_SETMEM (THREAD_SELF, dtv, dtvp) > > > +/* Return the address of the dtv for the current thread. */ > > > +# define THREAD_DTV() THREAD_GETMEM (THREAD_SELF, dtv) > > > > While at it, try to make the i386 version use that too? > > Yeah, I have not ported the improvements back to the 32-bit version; > maybe I should. Better always keep things as coherent as possible. Otherwise another you will later wonder why in the hell we have differences between the two versions. > Another cool one is doing fs/gs-relative access using > GCC's __seg_fs/__seg_gs when supported. Yes, that's nice indeed! Samuel