Sergey Bugaev, le dim. 12 févr. 2023 14:10:42 +0300, a ecrit: > It seems that GCC expects TLS on x86_64 to be done relative to %fs, not %gs, > so > that's what I attempted to do in tls.h. The main thing missing there is the > ability to actually set (and read) the %fs base address of a thread. It is my > understanding (but note that I have no idea what I'm talking about) that on > x86_64 the segment descriptors (as in GDT/LDT) are not used for this,
segmentation has somewhat disappeared in x86_64, yes. > and instead the address can be set by writing to a MSR. Linux exposes > the arch_prctl (ARCH_[GS]ET_[FG]S) syscall for this; so maybe GNU Mach > could also have an explicit routine for this, perhaps like this: > > routine i386_set_fgs_base ( > target_thread: thread_t; > which: int; > value: rpc_vm_address_t); Indeed. > 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. > 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 ? > + int __glibc_padding3; > + /* Reservation of some values for the TM ABI. */ > + void *__private_tm[4]; > + /* GCC split stack support. */ > + void *__private_ss; > + /* The lowest address of shadow stack. */ > + unsigned long long int ssp_base; > + > + /* Keep these fields last, so offsets of fields above can continue being > + compatible with the x86_64 NPTL version. */ > + mach_port_t reply_port; /* This thread's reply port. */ > + struct hurd_sigstate *_hurd_sigstate; > + > + /* Used by the exception handling implementation in the dynamic loader. */ > + struct rtld_catch *rtld_catch; > +} tcbhead_t; > + > +/* 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? > +/* FIXME */ > +# define __LIBC_NO_TLS() 0 We'll want an efficient way to know whether we have configured TLS indeed. At worse we can make it a global variable. > +/* The TCB can have any size and the memory following the address the > + thread pointer points to is unspecified. Allocate the TCB there. */ > +# define TLS_TCB_AT_TP 1 > +# define TLS_DTV_AT_TP 0 > + Also copy the comment above TCB_ALIGNMENT. > +/* 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? Samuel