[PATCH 2/2] x86_64: Use __seg_fs qualifiers in NPTL accessors
Uros Bizjak
ubizjak@gmail.com
Sun Aug 17 15:49:55 GMT 2025
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
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