[PATCH v2] x86_64: Use __seg_fs qualifiers in NPTL accessors
H.J. Lu
hjl.tools@gmail.com
Wed Aug 20 20:31:04 GMT 2025
On Wed, Aug 20, 2025 at 1:21 PM Uros Bizjak <ubizjak@gmail.com> wrote:
>
> For 64-bit, use __seg_fs named address space qualifiers to cast NPTL
> accessors to %fs: prefixed addresses. Use volatile access only where
> strictly necessary.
>
> Move x32 implementations to sysdeps/x86_64/x32/nptl to work around
> the GCC bug:
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121613
>
> While moving x32 implementations, change %P asm operand modifier to %c
> and add missing casts to (long long int) of index variable in *_MC
> TCB accessors.
>
> Co-Authored-By: H.J. Lu <hjl.tools@gmail.com>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
> Cc: Florian Weimer <fweimer@redhat.com>
> Cc: Carlos O'Donell <carlos@redhat.com>
> ---
> v2: Move x32 implementations to sysdeps/x86_64/x32/nptl.
> ---
> sysdeps/unix/sysv/linux/x86_64/64/Implies | 1 +
> sysdeps/x86_64/64/nptl/rseq-access.h | 61 +++++++++++++++++
> sysdeps/x86_64/64/nptl/tcb-access.h | 75 +++++++++++++++++++++
> sysdeps/x86_64/nptl/tls.h | 4 --
> sysdeps/x86_64/{ => x32}/nptl/rseq-access.h | 20 +++---
> sysdeps/x86_64/{ => x32}/nptl/tcb-access.h | 55 +++++++++------
> 6 files changed, 181 insertions(+), 35 deletions(-)
> create mode 100644 sysdeps/unix/sysv/linux/x86_64/64/Implies
> create mode 100644 sysdeps/x86_64/64/nptl/rseq-access.h
> create mode 100644 sysdeps/x86_64/64/nptl/tcb-access.h
> rename sysdeps/x86_64/{ => x32}/nptl/rseq-access.h (85%)
> rename sysdeps/x86_64/{ => x32}/nptl/tcb-access.h (75%)
>
> diff --git a/sysdeps/unix/sysv/linux/x86_64/64/Implies b/sysdeps/unix/sysv/linux/x86_64/64/Implies
> new file mode 100644
> index 0000000000..f379d95141
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/x86_64/64/Implies
> @@ -0,0 +1 @@
> +x86_64/64/nptl
> diff --git a/sysdeps/x86_64/64/nptl/rseq-access.h b/sysdeps/x86_64/64/nptl/rseq-access.h
> new file mode 100644
> index 0000000000..214cb96797
> --- /dev/null
> +++ b/sysdeps/x86_64/64/nptl/rseq-access.h
> @@ -0,0 +1,61 @@
> +/* RSEQ_* accessors. x86_64 version.
> + Copyright (C) 2002-2025 Free Software Foundation, Inc.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +/* Read member of the RSEQ area directly. */
> +#define RSEQ_GETMEM(member) \
> + ({ \
> + _Static_assert (sizeof (RSEQ_SELF()->member) == 1 \
> + || sizeof (RSEQ_SELF()->member) == 4 \
> + || sizeof (RSEQ_SELF()->member) == 8, \
> + "size of rseq data"); \
> + (*(__typeof (RSEQ_SELF()->member) __seg_fs *) \
> + (__rseq_offset + offsetof (struct rseq_area, member))); \
> + })
> +
> +/* Read member of the RSEQ area directly, with single-copy atomicity semantics. */
> +#define RSEQ_GETMEM_ONCE(member) \
> + ({ \
> + _Static_assert (sizeof (RSEQ_SELF()->member) == 1 \
> + || sizeof (RSEQ_SELF()->member) == 4 \
> + || sizeof (RSEQ_SELF()->member) == 8, \
> + "size of rseq data"); \
> + (*(volatile __typeof (RSEQ_SELF()->member) __seg_fs *) \
> + (__rseq_offset + offsetof (struct rseq_area, member))); \
> + })
> +
> +/* Set member of the RSEQ area directly. */
> +#define RSEQ_SETMEM(member, value) \
> + ({ \
> + _Static_assert (sizeof (RSEQ_SELF()->member) == 1 \
> + || sizeof (RSEQ_SELF()->member) == 4 \
> + || sizeof (RSEQ_SELF()->member) == 8, \
> + "size of rseq data"); \
> + (*(__typeof (RSEQ_SELF()->member) __seg_fs *) \
> + (__rseq_offset + offsetof (struct rseq_area, member)) = (value)); \
> + })
> +
> +/* Set member of the RSEQ area directly, with single-copy atomicity semantics. */
> +#define RSEQ_SETMEM_ONCE(member, value) \
> + ({ \
> + _Static_assert (sizeof (RSEQ_SELF()->member) == 1 \
> + || sizeof (RSEQ_SELF()->member) == 4 \
> + || sizeof (RSEQ_SELF()->member) == 8, \
> + "size of rseq data"); \
> + (*(volatile __typeof (RSEQ_SELF()->member) __seg_fs *) \
> + (__rseq_offset + offsetof (struct rseq_area, member)) = (value)); \
> + })
> diff --git a/sysdeps/x86_64/64/nptl/tcb-access.h b/sysdeps/x86_64/64/nptl/tcb-access.h
> new file mode 100644
> index 0000000000..d5b9d99f2e
> --- /dev/null
> +++ b/sysdeps/x86_64/64/nptl/tcb-access.h
> @@ -0,0 +1,75 @@
> +/* THREAD_* accessors. x86_64 version.
> + Copyright (C) 2002-2025 Free Software Foundation, Inc.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +/* Return the thread descriptor for the current thread. */
> +#define THREAD_SELF \
> + (*(struct pthread *__seg_fs *) offsetof (struct pthread, header.self))
> +
> +/* Read member of the thread descriptor directly. */
> +#define THREAD_GETMEM(descr, member) \
> + ({ \
> + _Static_assert (sizeof (descr->member) == 1 \
> + || sizeof (descr->member) == 4 \
> + || sizeof (descr->member) == 8, \
> + "size of per-thread data"); \
> + (*(__typeof (descr->member) __seg_fs *) \
> + offsetof (struct pthread, member)); \
> + })
> +
> +#define THREAD_GETMEM_VOLATILE(descr, member) \
> + ({ \
> + _Static_assert (sizeof (descr->member) == 1 \
> + || sizeof (descr->member) == 4 \
> + || sizeof (descr->member) == 8, \
> + "size of per-thread data"); \
> + (*(volatile __typeof (descr->member) __seg_fs *) \
> + offsetof (struct pthread, member)); \
> + })
> +
> +/* Same as THREAD_GETMEM, but the member offset can be non-constant. */
> +#define THREAD_GETMEM_NC(descr, member, idx) \
> + ({ \
> + _Static_assert (sizeof (descr->member[0]) == 1 \
> + || sizeof (descr->member[0]) == 4 \
> + || sizeof (descr->member[0]) == 8, \
> + "size of per-thread data"); \
> + (*(__typeof (descr->member[0]) __seg_fs *) \
> + offsetof (struct pthread, member[idx])); \
> + })
> +
> +/* Set member of the thread descriptor directly. */
> +#define THREAD_SETMEM(descr, member, value) \
> + ({ \
> + _Static_assert (sizeof (descr->member) == 1 \
> + || sizeof (descr->member) == 4 \
> + || sizeof (descr->member) == 8, \
> + "size of per-thread data"); \
> + (*(__typeof (descr->member) __seg_fs *) \
> + offsetof (struct pthread, member) = (value)); \
> + })
> +
> +/* Same as THREAD_SETMEM, but the member offset can be non-constant. */
> +#define THREAD_SETMEM_NC(descr, member, idx, value) \
> + ({ \
> + _Static_assert (sizeof (descr->member[0]) == 1 \
> + || sizeof (descr->member[0]) == 4 \
> + || sizeof (descr->member[0]) == 8, \
> + "size of per-thread data"); \
> + (*(__typeof (descr->member[0]) __seg_fs *) \
> + offsetof (struct pthread, member[idx]) = (value)); \
> + })
> diff --git a/sysdeps/x86_64/nptl/tls.h b/sysdeps/x86_64/nptl/tls.h
> index 29b028cdcd..123208a781 100644
> --- a/sysdeps/x86_64/nptl/tls.h
> +++ b/sysdeps/x86_64/nptl/tls.h
> @@ -168,10 +168,6 @@ _Static_assert (offsetof (tcbhead_t, __glibc_unused2) == 0x80,
> THREAD_GETMEM (__pd, header.dtv); })
>
>
> -/* Return the thread descriptor for the current thread. */
> -# define THREAD_SELF \
> - (*(struct pthread *__seg_fs *) offsetof (struct pthread, header.self))
> -
> /* Magic for libthread_db to know how to do THREAD_SELF. */
> # define DB_THREAD_SELF_INCLUDE <sys/reg.h> /* For the FS constant. */
> # define DB_THREAD_SELF CONST_THREAD_AREA (64, FS)
> diff --git a/sysdeps/x86_64/nptl/rseq-access.h b/sysdeps/x86_64/x32/nptl/rseq-access.h
> similarity index 85%
> rename from sysdeps/x86_64/nptl/rseq-access.h
> rename to sysdeps/x86_64/x32/nptl/rseq-access.h
> index bc966b2972..1aeb22b763 100644
> --- a/sysdeps/x86_64/nptl/rseq-access.h
> +++ b/sysdeps/x86_64/x32/nptl/rseq-access.h
> @@ -1,5 +1,5 @@
> -/* RSEQ_* accessors. x86_64 version.
> - Copyright (C) 2002-2025 Free Software Foundation, Inc.
> +/* RSEQ_* accessors. x32 version.
> + Copyright (C) 2025 Free Software Foundation, Inc.
> This file is part of the GNU C Library.
>
> The GNU C Library is free software; you can redistribute it and/or
> @@ -22,20 +22,20 @@
> _Static_assert (sizeof (__value) == 1 \
> || sizeof (__value) == 4 \
> || sizeof (__value) == 8, \
> - "size of rseq data"); \
> + "size of rseq data"); \
> if (sizeof (__value) == 1) \
> - asm volatile ("movb %%fs:%P2(%q3),%b0" \
> + asm volatile ("movb %%fs:%c2(%q3),%b0" \
> : "=q" (__value) \
> : "0" (0), "i" (offsetof (struct rseq_area, member)), \
> "r" ((long long int) __rseq_offset)); \
> else if (sizeof (__value) == 4) \
> - asm volatile ("movl %%fs:%P1(%q2),%0" \
> + asm volatile ("movl %%fs:%c1(%q2),%0" \
> : "=r" (__value) \
> : "i" (offsetof (struct rseq_area, member)), \
> "r" ((long long int) __rseq_offset)); \
> else /* 8 */ \
> { \
> - asm volatile ("movq %%fs:%P1(%q2),%q0" \
> + asm volatile ("movq %%fs:%c1(%q2),%q0" \
> : "=r" (__value) \
> : "i" (offsetof (struct rseq_area, member)), \
> "r" ((long long int) __rseq_offset)); \
> @@ -51,14 +51,14 @@
> _Static_assert (sizeof (RSEQ_SELF()->member) == 1 \
> || sizeof (RSEQ_SELF()->member) == 4 \
> || sizeof (RSEQ_SELF()->member) == 8, \
> - "size of rseq data"); \
> + "size of rseq data"); \
> if (sizeof (RSEQ_SELF()->member) == 1) \
> - asm volatile ("movb %b0,%%fs:%P1(%q2)" : \
> + asm volatile ("movb %b0,%%fs:%c1(%q2)" : \
> : "iq" (value), \
> "i" (offsetof (struct rseq_area, member)), \
> "r" ((long long int) __rseq_offset)); \
> else if (sizeof (RSEQ_SELF()->member) == 4) \
> - asm volatile ("movl %0,%%fs:%P1(%q2)" : \
> + asm volatile ("movl %0,%%fs:%c1(%q2)" : \
> : IMM_MODE (value), \
> "i" (offsetof (struct rseq_area, member)), \
> "r" ((long long int) __rseq_offset)); \
> @@ -67,7 +67,7 @@
> /* Since movq takes a signed 32-bit immediate or a register source \
> operand, use "er" constraint for 32-bit signed integer constant \
> or register. */ \
> - asm volatile ("movq %q0,%%fs:%P1(%q2)" : \
> + asm volatile ("movq %q0,%%fs:%c1(%q2)" : \
> : "er" ((uint64_t) cast_to_integer (value)), \
> "i" (offsetof (struct rseq_area, member)), \
> "r" ((long long int) __rseq_offset)); \
> diff --git a/sysdeps/x86_64/nptl/tcb-access.h b/sysdeps/x86_64/x32/nptl/tcb-access.h
> similarity index 75%
> rename from sysdeps/x86_64/nptl/tcb-access.h
> rename to sysdeps/x86_64/x32/nptl/tcb-access.h
> index defd76f54f..817c660750 100644
> --- a/sysdeps/x86_64/nptl/tcb-access.h
> +++ b/sysdeps/x86_64/x32/nptl/tcb-access.h
> @@ -1,5 +1,5 @@
> -/* THREAD_* accessors. x86_64 version.
> - Copyright (C) 2002-2025 Free Software Foundation, Inc.
> +/* THREAD_* accessors. x32 version.
> + Copyright (C) 2025 Free Software Foundation, Inc.
> This file is part of the GNU C Library.
>
> The GNU C Library is free software; you can redistribute it and/or
> @@ -16,6 +16,18 @@
> License along with the GNU C Library; if not, see
> <https://www.gnu.org/licenses/>. */
>
> +/* Return the thread descriptor for the current thread.
> +
> + The contained asm must *not* be marked volatile since otherwise
> + assignments like
> + pthread_descr self = thread_self();
> + do not get optimized away. */
> +#define THREAD_SELF \
> + ({ struct pthread *__self; \
> + asm ("mov %%fs:%c1,%0" : "=r" (__self) \
> + : "i" (offsetof (struct pthread, header.self))); \
> + __self; })
> +
> /* Read member of the thread descriptor directly. */
> # define THREAD_GETMEM(descr, member) \
> ({ __typeof (descr->member) __value; \
> @@ -24,16 +36,16 @@
> || sizeof (__value) == 8, \
> "size of per-thread data"); \
> if (sizeof (__value) == 1) \
> - asm volatile ("movb %%fs:%P2,%b0" \
> + asm volatile ("movb %%fs:%c2,%b0" \
> : "=q" (__value) \
> : "0" (0), "i" (offsetof (struct pthread, member))); \
> else if (sizeof (__value) == 4) \
> - asm volatile ("movl %%fs:%P1,%0" \
> + asm volatile ("movl %%fs:%c1,%0" \
> : "=r" (__value) \
> : "i" (offsetof (struct pthread, member))); \
> - else /* 8 */ \
> + else /* 8 */ \
> { \
> - asm volatile ("movq %%fs:%P1,%q0" \
> + asm volatile ("movq %%fs:%c1,%q0" \
> : "=r" (__value) \
> : "i" (offsetof (struct pthread, member))); \
> } \
> @@ -50,20 +62,21 @@
> || sizeof (__value) == 8, \
> "size of per-thread data"); \
> if (sizeof (__value) == 1) \
> - asm volatile ("movb %%fs:%P2(%q3),%b0" \
> + asm volatile ("movb %%fs:%c2(%q3),%b0" \
> : "=q" (__value) \
> : "0" (0), "i" (offsetof (struct pthread, member[0])), \
> - "r" (idx)); \
> + "r" ((long long int) idx)); \
> else if (sizeof (__value) == 4) \
> - asm volatile ("movl %%fs:%P1(,%q2,4),%0" \
> + asm volatile ("movl %%fs:%c1(,%q2,4),%0" \
> : "=r" (__value) \
> - : "i" (offsetof (struct pthread, member[0])), "r" (idx));\
> + : "i" (offsetof (struct pthread, member[0])), \
> + "r" ((long long int) idx)); \
> else /* 8 */ \
> { \
> - asm volatile ("movq %%fs:%P1(,%q2,8),%q0" \
> + asm volatile ("movq %%fs:%c1(,%q2,8),%q0" \
> : "=r" (__value) \
> : "i" (offsetof (struct pthread, member[0])), \
> - "r" (idx)); \
> + "r" ((long long int) idx)); \
> } \
> __value; })
>
> @@ -85,11 +98,11 @@
> || sizeof (descr->member) == 8, \
> "size of per-thread data"); \
> if (sizeof (descr->member) == 1) \
> - asm volatile ("movb %b0,%%fs:%P1" : \
> + asm volatile ("movb %b0,%%fs:%c1" : \
> : "iq" (value), \
> "i" (offsetof (struct pthread, member))); \
> else if (sizeof (descr->member) == 4) \
> - asm volatile ("movl %0,%%fs:%P1" : \
> + asm volatile ("movl %0,%%fs:%c1" : \
> : IMM_MODE (value), \
> "i" (offsetof (struct pthread, member))); \
> else /* 8 */ \
> @@ -97,7 +110,7 @@
> /* Since movq takes a signed 32-bit immediate or a register source \
> operand, use "er" constraint for 32-bit signed integer constant \
> or register. */ \
> - asm volatile ("movq %q0,%%fs:%P1" : \
> + asm volatile ("movq %q0,%%fs:%c1" : \
> : "er" ((uint64_t) cast_to_integer (value)), \
> "i" (offsetof (struct pthread, member))); \
> }})
> @@ -111,22 +124,22 @@
> || sizeof (descr->member[0]) == 8, \
> "size of per-thread data"); \
> if (sizeof (descr->member[0]) == 1) \
> - asm volatile ("movb %b0,%%fs:%P1(%q2)" : \
> + asm volatile ("movb %b0,%%fs:%c1(%q2)" : \
> : "iq" (value), \
> "i" (offsetof (struct pthread, member[0])), \
> - "r" (idx)); \
> + "r" ((long long int) idx)); \
> else if (sizeof (descr->member[0]) == 4) \
> - asm volatile ("movl %0,%%fs:%P1(,%q2,4)" : \
> + asm volatile ("movl %0,%%fs:%c1(,%q2,4)" : \
> : IMM_MODE (value), \
> "i" (offsetof (struct pthread, member[0])), \
> - "r" (idx)); \
> + "r" ((long long int) idx)); \
> else /* 8 */ \
> { \
> /* Since movq takes a signed 32-bit immediate or a register source \
> operand, use "er" constraint for 32-bit signed integer constant \
> or register. */ \
> - asm volatile ("movq %q0,%%fs:%P1(,%q2,8)" : \
> + asm volatile ("movq %q0,%%fs:%c1(,%q2,8)" : \
> : "er" ((uint64_t) cast_to_integer (value)), \
> "i" (offsetof (struct pthread, member[0])), \
> - "r" (idx)); \
> + "r" ((long long int) idx)); \
> }})
> --
> 2.50.1
>
LGTM.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
Thanks.
--
H.J.
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