[PATCH 2/2] x86_64: Use __seg_fs qualifiers in NPTL accessors
H.J. Lu
hjl.tools@gmail.com
Wed Aug 20 03:06:03 GMT 2025
On Sun, Aug 17, 2025 at 8:50 AM Uros Bizjak <ubizjak@gmail.com> wrote:
>
> Use __seg_fs named address space qualifiers to cast NPTL accessors
> to %fs: prefixed addresses. Use volatile access only where
> strictly necessary.
>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Cc: H.J.Lu <hjl.tools@gmail.com>
> Cc: Florian Weimer <fweimer@redhat.com>
> Cc: Carlos O'Donell <carlos@redhat.com>
> ---
> sysdeps/x86_64/nptl/rseq-access.h | 82 ++++++++-----------
> sysdeps/x86_64/nptl/tcb-access.h | 127 ++++++++----------------------
> 2 files changed, 66 insertions(+), 143 deletions(-)
>
> diff --git a/sysdeps/x86_64/nptl/rseq-access.h b/sysdeps/x86_64/nptl/rseq-access.h
> index bc966b2972..214cb96797 100644
> --- a/sysdeps/x86_64/nptl/rseq-access.h
> +++ b/sysdeps/x86_64/nptl/rseq-access.h
> @@ -16,34 +16,38 @@
> 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) \
> - ({ __typeof (RSEQ_SELF()->member) __value; \
> - _Static_assert (sizeof (__value) == 1 \
> - || sizeof (__value) == 4 \
> - || sizeof (__value) == 8, \
> - "size of rseq data"); \
> - if (sizeof (__value) == 1) \
> - asm volatile ("movb %%fs:%P2(%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" \
> - : "=r" (__value) \
> - : "i" (offsetof (struct rseq_area, member)), \
> - "r" ((long long int) __rseq_offset)); \
> - else /* 8 */ \
> - { \
> - asm volatile ("movq %%fs:%P1(%q2),%q0" \
> - : "=r" (__value) \
> - : "i" (offsetof (struct rseq_area, member)), \
> - "r" ((long long int) __rseq_offset)); \
> - } \
> - __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))); \
> + })
>
> -/* Read member of the RSEQ area directly. */
> -#define RSEQ_GETMEM(member) RSEQ_GETMEM_ONCE(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) \
> @@ -51,27 +55,7 @@
> _Static_assert (sizeof (RSEQ_SELF()->member) == 1 \
> || sizeof (RSEQ_SELF()->member) == 4 \
> || sizeof (RSEQ_SELF()->member) == 8, \
> - "size of rseq data"); \
> - if (sizeof (RSEQ_SELF()->member) == 1) \
> - asm volatile ("movb %b0,%%fs:%P1(%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)" : \
> - : IMM_MODE (value), \
> - "i" (offsetof (struct rseq_area, member)), \
> - "r" ((long long int) __rseq_offset)); \
> - 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)" : \
> - : "er" ((uint64_t) cast_to_integer (value)), \
> - "i" (offsetof (struct rseq_area, member)), \
> - "r" ((long long int) __rseq_offset)); \
> - }})
> -
> -/* Set member of the RSEQ area directly. */
> -#define RSEQ_SETMEM(member, value) RSEQ_SETMEM_ONCE(member, value)
> + "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/nptl/tcb-access.h b/sysdeps/x86_64/nptl/tcb-access.h
> index defd76f54f..445f328ac2 100644
> --- a/sysdeps/x86_64/nptl/tcb-access.h
> +++ b/sysdeps/x86_64/nptl/tcb-access.h
> @@ -17,116 +17,55 @@
> <https://www.gnu.org/licenses/>. */
>
> /* Read member of the thread descriptor directly. */
> -# define THREAD_GETMEM(descr, member) \
> - ({ __typeof (descr->member) __value; \
> - _Static_assert (sizeof (__value) == 1 \
> - || sizeof (__value) == 4 \
> - || sizeof (__value) == 8, \
> +#define THREAD_GETMEM(descr, member) \
> + ({ \
> + _Static_assert (sizeof (descr->member) == 1 \
> + || sizeof (descr->member) == 4 \
> + || sizeof (descr->member) == 8, \
> "size of per-thread data"); \
> - if (sizeof (__value) == 1) \
> - asm volatile ("movb %%fs:%P2,%b0" \
> - : "=q" (__value) \
> - : "0" (0), "i" (offsetof (struct pthread, member))); \
> - else if (sizeof (__value) == 4) \
> - asm volatile ("movl %%fs:%P1,%0" \
> - : "=r" (__value) \
> - : "i" (offsetof (struct pthread, member))); \
> - else /* 8 */ \
> - { \
> - asm volatile ("movq %%fs:%P1,%q0" \
> - : "=r" (__value) \
> - : "i" (offsetof (struct pthread, member))); \
> - } \
> - __value; })
> + (*(__typeof (descr->member) __seg_fs *) \
> + offsetof (struct pthread, member)); \
> + })
>
> -/* THREAD_GETMEM already forces a read. */
> -#define THREAD_GETMEM_VOLATILE(descr, member) THREAD_GETMEM (descr, 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) \
> - ({ __typeof (descr->member[0]) __value; \
> - _Static_assert (sizeof (__value) == 1 \
> - || sizeof (__value) == 4 \
> - || sizeof (__value) == 8, \
> +#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"); \
> - if (sizeof (__value) == 1) \
> - asm volatile ("movb %%fs:%P2(%q3),%b0" \
> - : "=q" (__value) \
> - : "0" (0), "i" (offsetof (struct pthread, member[0])), \
> - "r" (idx)); \
> - else if (sizeof (__value) == 4) \
> - asm volatile ("movl %%fs:%P1(,%q2,4),%0" \
> - : "=r" (__value) \
> - : "i" (offsetof (struct pthread, member[0])), "r" (idx));\
> - else /* 8 */ \
> - { \
> - asm volatile ("movq %%fs:%P1(,%q2,8),%q0" \
> - : "=r" (__value) \
> - : "i" (offsetof (struct pthread, member[0])), \
> - "r" (idx)); \
> - } \
> - __value; })
> -
> -
> -/* Loading addresses of objects on x86-64 needs to be treated special
> - when generating PIC code. */
> -#ifdef __pic__
> -# define IMM_MODE "nr"
> -#else
> -# define IMM_MODE "ir"
> -#endif
> -
> + (*(__typeof (descr->member[0]) __seg_fs *) \
> + offsetof (struct pthread, member[idx])); \
> + })
>
> /* 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 \
> || sizeof (descr->member) == 8, \
> "size of per-thread data"); \
> - if (sizeof (descr->member) == 1) \
> - asm volatile ("movb %b0,%%fs:%P1" : \
> - : "iq" (value), \
> - "i" (offsetof (struct pthread, member))); \
> - else if (sizeof (descr->member) == 4) \
> - asm volatile ("movl %0,%%fs:%P1" : \
> - : IMM_MODE (value), \
> - "i" (offsetof (struct pthread, member))); \
> - 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" : \
> - : "er" ((uint64_t) cast_to_integer (value)), \
> - "i" (offsetof (struct pthread, member))); \
> - }})
> -
> + (*(__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) \
> +#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"); \
> - if (sizeof (descr->member[0]) == 1) \
> - asm volatile ("movb %b0,%%fs:%P1(%q2)" : \
> - : "iq" (value), \
> - "i" (offsetof (struct pthread, member[0])), \
> - "r" (idx)); \
> - else if (sizeof (descr->member[0]) == 4) \
> - asm volatile ("movl %0,%%fs:%P1(,%q2,4)" : \
> - : IMM_MODE (value), \
> - "i" (offsetof (struct pthread, member[0])), \
> - "r" (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)" : \
> - : "er" ((uint64_t) cast_to_integer (value)), \
> - "i" (offsetof (struct pthread, member[0])), \
> - "r" (idx)); \
> - }})
> + (*(__typeof (descr->member[0]) __seg_fs *) \
> + offsetof (struct pthread, member[idx]) = (value)); \
> + })
> --
> 2.50.1
>
This doesn't work for x32:
../localedata/gen-locale.sh: line 29: 3948007 Segmentation fault
(core dumped) ${localedef_before_env} ${run_program_env}
I18NPATH=../localedata ${localedef_after_env} $flags -f $charmap -i
$input ${common_objpfx}localedata/$out
Charmap: "UTF-8" Inputfile: "C" Outputdir: "C.UTF-8" failed
/bin/sh: line 4:
/export/build/gnu/tools-build/glibc-x32-cet-gitlab/build-x86_64-linux/localedata/C.UTF-8/LC_CTYPE.test-result:
No such file or directory
make[4]: *** [../gen-locales.mk:28:
/export/build/gnu/tools-build/glibc-x32-cet-gitlab/build-x86_64-linux/localedata/C.UTF-8/LC_CTYPE]
Error 1
--
H.J.
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