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Re: [PATCH 1/3] hurd: i386 TLS tweaks
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From: |
Samuel Thibault |
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Subject: |
Re: [PATCH 1/3] hurd: i386 TLS tweaks |
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Date: |
Tue, 14 Feb 2023 20:27:16 +0100 |
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User-agent: |
NeoMutt/20170609 (1.8.3) |
Applied, thanks!
Sergey Bugaev via Libc-alpha, le mar. 14 févr. 2023 20:37:20 +0300, a ecrit:
> * Micro-optimize TLS access using GCC's native support for gs-based
> addressing when available;
> * Just use THREAD_GETMEM and THREAD_SETMEM instead of more inline
> assembly;
> * Sync tcbhead_t layout with NPTL, in particular update/fix __private_ss
> offset;
> * Statically assert that the two offsets that are a part of ABI are what
> we expect them to be.
>
> Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
> ---
> sysdeps/mach/hurd/i386/tls.h | 48 ++++++++++++++++++++++++++----------
> 1 file changed, 35 insertions(+), 13 deletions(-)
>
> diff --git a/sysdeps/mach/hurd/i386/tls.h b/sysdeps/mach/hurd/i386/tls.h
> index a6ff0107..dc43d4c7 100644
> --- a/sysdeps/mach/hurd/i386/tls.h
> +++ b/sysdeps/mach/hurd/i386/tls.h
> @@ -38,11 +38,12 @@ typedef struct
> uintptr_t stack_guard;
> uintptr_t pointer_guard;
> int gscope_flag;
> - int private_futex;
> + unsigned int feature_1;
> /* Reservation of some values for the TM ABI. */
> - void *__private_tm[4];
> + void *__private_tm[3];
> /* GCC split stack support. */
> void *__private_ss;
> + void *__glibc_padding1;
>
> /* Keep these fields last, so offsets of fields above can continue being
> compatible with the i386 Linux version. */
> @@ -53,6 +54,13 @@ typedef struct
> struct rtld_catch *rtld_catch;
> } tcbhead_t;
>
> +/* GCC generates %gs:0x14 to access the stack guard. */
> +_Static_assert (offsetof (tcbhead_t, stack_guard) == 0x14,
> + "stack guard offset");
> +/* libgcc uses %gs:0x30 to access the split stack pointer. */
> +_Static_assert (offsetof (tcbhead_t, __private_ss) == 0x30,
> + "split stack pointer offset");
> +
> /* Return tcbhead_t from a TLS segment descriptor. */
> # define HURD_DESC_TLS(desc) \
> ({ \
> @@ -166,8 +174,25 @@ out:
> # define TLS_INIT_TP(descr) \
> _hurd_tls_init ((tcbhead_t *) (descr))
>
> +# if __GNUC_PREREQ (6, 0)
> +
> +# define THREAD_SELF
> \
> + (*(tcbhead_t * __seg_gs *) offsetof (tcbhead_t, tcb))
> +# define THREAD_GETMEM(descr, member)
> \
> + (*(__typeof (descr->member) __seg_gs *) offsetof (tcbhead_t, member))
> +# define THREAD_GETMEM_NC(descr, member, idx)
> \
> + (*(__typeof (descr->member[0]) __seg_gs *) \
> + (offsetof (tcbhead_t, member) + (idx) * sizeof (descr->member[0])))
> +# define THREAD_SETMEM(descr, member, value)
> \
> + (*(__typeof (descr->member) __seg_gs *) offsetof (tcbhead_t, member) =
> value)
> +# define THREAD_SETMEM_NC(descr, member, index, value)
> \
> + (*(__typeof (descr->member[0]) __seg_gs *) \
> + (offsetof (tcbhead_t, member) + (idx) * sizeof (descr->member[0])))
> +
> +# else
> +
> /* Return the TCB address of the current thread. */
> -# define THREAD_SELF \
> +# define THREAD_SELF
> \
> ({ tcbhead_t *__tcb;
> \
> __asm__ ("movl %%gs:%c1,%0" : "=r" (__tcb)
> \
> : "i" (offsetof (tcbhead_t, tcb))); \
> @@ -200,7 +225,7 @@ out:
>
>
> /* Same as THREAD_GETMEM, but the member offset can be non-constant. */
> -# define THREAD_GETMEM_NC(descr, member, idx) \
> +# define THREAD_GETMEM_NC(descr, member, idx) \
> ({ __typeof (descr->member[0]) __value; \
> _Static_assert (sizeof (__value) == 1 \
> || sizeof (__value) == 4 \
> @@ -229,7 +254,7 @@ out:
>
>
> /* Set member of the thread descriptor directly. */
> -# define THREAD_SETMEM(descr, member, value) \
> +# define THREAD_SETMEM(descr, member, value) \
> ({ \
> _Static_assert (sizeof (descr->member) == 1 \
> || sizeof (descr->member) == 4 \
> @@ -254,7 +279,7 @@ out:
>
>
> /* Same as THREAD_SETMEM, but the member offset can be non-constant. */
> -# define THREAD_SETMEM_NC(descr, member, idx, value) \
> +# define THREAD_SETMEM_NC(descr, member, idx, value) \
> ({ \
> _Static_assert (sizeof (descr->member[0]) == 1 \
> || sizeof (descr->member[0]) == 4 \
> @@ -279,6 +304,8 @@ out:
> "r" (idx)); \
> }})
>
> +# endif /* __GNUC_PREREQ (6, 0) */
> +
> /* Return the TCB address of a thread given its state.
> Note: this is expensive. */
> # define THREAD_TCB(thread, thread_state) \
> @@ -295,15 +322,10 @@ out:
> HURD_DESC_TLS (___desc);})
>
> /* Install new dtv for current thread. */
> -# define INSTALL_NEW_DTV(dtvp)
> \
> - ({ asm volatile ("movl %0,%%gs:%P1"
> \
> - : : "ir" (dtvp), "i" (offsetof (tcbhead_t, dtv))); })
> +# define INSTALL_NEW_DTV(dtvp) THREAD_SETMEM (THREAD_SELF, dtv, dtvp)
>
> /* Return the address of the dtv for the current thread. */
> -# define THREAD_DTV()
> \
> - ({ dtv_t *_dtv; \
> - asm ("movl %%gs:%P1,%0" : "=q" (_dtv) : "i" (offsetof (tcbhead_t,
> dtv)));\
> - _dtv; })
> +# define THREAD_DTV() THREAD_GETMEM (THREAD_SELF, dtv)
>
>
> /* Set the stack guard field in TCB head. */
> --
> 2.39.1
>
--
Samuel
---
Pour une évaluation indépendante, transparente et rigoureuse !
Je soutiens la Commission d'Évaluation de l'Inria.