From: Samuel Thibault <samuel.thibault@gnu.org>
To: Sergey Bugaev <bugaevc@gmail.com>
Cc: bug-hurd@gnu.org, libc-alpha@sourceware.org,
"Flávio Cruz" <flaviocruz@gmail.com>
Subject: Re: [RFC PATCH glibc 11/12] hurd, htl: Add some x86_64-specific code
Date: Sun, 12 Feb 2023 17:11:53 +0100 [thread overview]
Message-ID: <20230212161153.q4km4h2ql3k5pasp@begin> (raw)
In-Reply-To: <20230212111044.610942-12-bugaevc@gmail.com>
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
next prev parent reply other threads:[~2023-02-12 16:11 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-12 11:10 [RFC PATCH 0/12] Towards glibc on x86_64-gnu Sergey Bugaev
2023-02-12 11:10 ` [RFC PATCH glibc 1/12] hurd: Refactor readlinkat() Sergey Bugaev
2023-02-12 14:49 ` Samuel Thibault
2023-02-12 11:10 ` [RFC PATCH glibc 2/12] hurd: Use mach_msg_type_number_t where appropriate Sergey Bugaev
2023-02-12 14:52 ` Samuel Thibault
2023-02-12 11:10 ` [RFC PATCH glibc 3/12] mach, hurd: Cast through uintptr_t Sergey Bugaev
2023-02-12 14:55 ` Samuel Thibault
2023-02-12 11:10 ` [RFC PATCH glibc 4/12] hurd: Fix xattr error value Sergey Bugaev
2023-02-12 14:56 ` Samuel Thibault
2023-02-12 11:10 ` [RFC PATCH glibc 5/12] htl: Fix semaphore reference Sergey Bugaev
2023-02-12 14:57 ` Samuel Thibault
2023-02-12 11:10 ` [RFC PATCH hurd 6/12] hurd: Fix modes_t and speeds_t types on 64-bit Sergey Bugaev
2023-02-12 15:00 ` Samuel Thibault
2023-02-12 15:15 ` Sergey Bugaev
2023-02-12 15:22 ` Samuel Thibault
2023-02-12 16:13 ` Sergey Bugaev
2023-02-12 16:30 ` Samuel Thibault
2023-02-12 19:03 ` Samuel Thibault
2023-02-12 11:10 ` [RFC PATCH mig 7/12] Drop -undef -ansi from cpp flags Sergey Bugaev
2023-02-12 15:01 ` Samuel Thibault
2023-02-12 18:43 ` Flávio Cruz
2023-02-12 18:44 ` Samuel Thibault
2023-02-12 11:10 ` [RFC PATCH mig 8/12] Set max type alignment to sizeof(long) Sergey Bugaev
2023-02-12 11:10 ` [RFC PATCH glibc 9/12] mach: Look for mach_i386.defs on x86_64 too Sergey Bugaev
2023-02-12 15:07 ` Samuel Thibault
2023-02-12 15:38 ` Sergey Bugaev
2023-02-12 15:46 ` Samuel Thibault
2023-02-12 16:01 ` Sergey Bugaev
2023-02-16 20:22 ` Joseph Myers
2023-02-12 11:10 ` [RFC PATCH glibc 10/12] hurd: Set up the basic tree for x86_64-gnu Sergey Bugaev
2023-02-12 15:15 ` Samuel Thibault
2023-02-12 11:10 ` [RFC PATCH glibc 11/12] hurd, htl: Add some x86_64-specific code Sergey Bugaev
2023-02-12 16:11 ` Samuel Thibault [this message]
2023-02-12 16:25 ` Sergey Bugaev
2023-02-12 16:36 ` Samuel Thibault
2023-02-12 16:40 ` Florian Weimer
2023-02-12 16:46 ` Samuel Thibault
2023-02-12 19:29 ` Florian Weimer
2023-02-12 19:37 ` Samuel Thibault
2023-02-12 16:51 ` Sergey Bugaev
2023-02-12 17:02 ` Samuel Thibault
2023-02-12 17:06 ` Sergey Bugaev
2023-02-12 11:10 ` [RFC PATCH glibc 12/12] C11 thrd: Downgrade the default alignment of mtx_t Sergey Bugaev
2023-02-12 15:18 ` Samuel Thibault
2023-02-12 15:52 ` Sergey Bugaev
2023-02-12 16:29 ` Samuel Thibault
2023-02-12 16:12 ` [RFC PATCH 0/12] Towards glibc on x86_64-gnu Samuel Thibault
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