[PATCH 1/4] x86: Simplify TCB access expressions
Uros Bizjak
ubizjak@gmail.com
Thu Sep 25 08:41:00 GMT 2025
Replace manual cast with a direct `(__typeof(*descr) __seg_gs *)0`
dereference to access `member`. This avoids redundant
`offsetof(struct pthread, member)` and improves readability while
preserving semantics.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
---
sysdeps/i386/nptl/tcb-access.h | 16 ++++++----------
sysdeps/i386/nptl/tls.h | 5 ++---
sysdeps/x86_64/nptl/tcb-access.h | 16 ++++++----------
sysdeps/x86_64/nptl/tls.h | 5 ++---
4 files changed, 16 insertions(+), 26 deletions(-)
diff --git a/sysdeps/i386/nptl/tcb-access.h b/sysdeps/i386/nptl/tcb-access.h
index 2a7f9d2a57..fdd84bd942 100644
--- a/sysdeps/i386/nptl/tcb-access.h
+++ b/sysdeps/i386/nptl/tcb-access.h
@@ -23,8 +23,7 @@
|| sizeof (descr->member) == 4 \
|| sizeof (descr->member) == 8, \
"size of per-thread data"); \
- (*(__typeof (descr->member) __seg_gs *) \
- offsetof (struct pthread, member)); \
+ ((__typeof (*descr) __seg_gs *)0)->member; \
})
#define THREAD_GETMEM_VOLATILE(descr, member) \
@@ -33,8 +32,8 @@
|| sizeof (descr->member) == 4 \
|| sizeof (descr->member) == 8, \
"size of per-thread data"); \
- (*(volatile __typeof (descr->member) __seg_gs *) \
- offsetof (struct pthread, member)); \
+ *(volatile __typeof (descr->member) __seg_gs *) \
+ &((__typeof (*descr) __seg_gs *)0)->member; \
})
/* Same as THREAD_GETMEM, but the member offset can be non-constant. */
@@ -44,8 +43,7 @@
|| sizeof (descr->member[0]) == 4 \
|| sizeof (descr->member[0]) == 8, \
"size of per-thread data"); \
- (*(__typeof (descr->member[0]) __seg_gs *) \
- offsetof (struct pthread, member[idx])); \
+ ((__typeof (*descr) __seg_gs *)0)->member[idx]; \
})
/* Set member of the thread descriptor directly. */
@@ -55,8 +53,7 @@
|| sizeof (descr->member) == 4 \
|| sizeof (descr->member) == 8, \
"size of per-thread data"); \
- (*(__typeof (descr->member) __seg_gs *) \
- offsetof (struct pthread, member) = (value)); \
+ ((__typeof (*descr) __seg_gs *)0)->member = (value); \
})
/* Same as THREAD_SETMEM, but the member offset can be non-constant. */
@@ -66,6 +63,5 @@
|| sizeof (descr->member[0]) == 4 \
|| sizeof (descr->member[0]) == 8, \
"size of per-thread data"); \
- (*(__typeof (descr->member[0]) __seg_gs *) \
- offsetof (struct pthread, member[idx]) = (value)); \
+ ((__typeof (*descr) __seg_gs *)0)->member[idx] = (value); \
})
diff --git a/sysdeps/i386/nptl/tls.h b/sysdeps/i386/nptl/tls.h
index 5c266c7191..7b297d4043 100644
--- a/sysdeps/i386/nptl/tls.h
+++ b/sysdeps/i386/nptl/tls.h
@@ -223,7 +223,7 @@ tls_fill_user_desc (union user_desc_init *desc,
/* Return the thread descriptor for the current thread. */
# define THREAD_SELF \
- (*(struct pthread *__seg_gs *) offsetof (struct pthread, header.self))
+ (*(struct pthread *__seg_gs *)&((struct pthread __seg_gs *)0)->header.self)
/* Magic for libthread_db to know how to do THREAD_SELF. */
# define DB_THREAD_SELF \
@@ -257,8 +257,7 @@ tls_fill_user_desc (union user_desc_init *desc,
{ int __res; \
asm volatile ("xchgl %1, %0" \
: "=r" (__res) \
- : "m" (*(int __seg_gs *) \
- offsetof (struct pthread, header.gscope_flag)), \
+ : "m" (((struct pthread __seg_gs *)0)->header.gscope_flag), \
"0" (THREAD_GSCOPE_FLAG_UNUSED)); \
if (__res == THREAD_GSCOPE_FLAG_WAIT) \
lll_futex_wake (&THREAD_SELF->header.gscope_flag, 1, LLL_PRIVATE); \
diff --git a/sysdeps/x86_64/nptl/tcb-access.h b/sysdeps/x86_64/nptl/tcb-access.h
index 445f328ac2..92b2da6cc6 100644
--- a/sysdeps/x86_64/nptl/tcb-access.h
+++ b/sysdeps/x86_64/nptl/tcb-access.h
@@ -23,8 +23,7 @@
|| sizeof (descr->member) == 4 \
|| sizeof (descr->member) == 8, \
"size of per-thread data"); \
- (*(__typeof (descr->member) __seg_fs *) \
- offsetof (struct pthread, member)); \
+ ((__typeof (*descr) __seg_fs *)0)->member; \
})
#define THREAD_GETMEM_VOLATILE(descr, member) \
@@ -33,8 +32,8 @@
|| sizeof (descr->member) == 4 \
|| sizeof (descr->member) == 8, \
"size of per-thread data"); \
- (*(volatile __typeof (descr->member) __seg_fs *) \
- offsetof (struct pthread, member)); \
+ *(volatile __typeof (descr->member) __seg_fs *) \
+ &((__typeof (*descr) __seg_fs *)0)->member; \
})
/* Same as THREAD_GETMEM, but the member offset can be non-constant. */
@@ -44,8 +43,7 @@
|| 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])); \
+ ((__typeof (*descr) __seg_fs *)0)->member[idx]; \
})
/* Set member of the thread descriptor directly. */
@@ -55,8 +53,7 @@
|| sizeof (descr->member) == 4 \
|| sizeof (descr->member) == 8, \
"size of per-thread data"); \
- (*(__typeof (descr->member) __seg_fs *) \
- offsetof (struct pthread, member) = (value)); \
+ ((__typeof (*descr) __seg_fs *)0)->member = (value); \
})
/* Same as THREAD_SETMEM, but the member offset can be non-constant. */
@@ -66,6 +63,5 @@
|| 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)); \
+ ((__typeof (*descr) __seg_fs *)0)->member[idx] = (value); \
})
diff --git a/sysdeps/x86_64/nptl/tls.h b/sysdeps/x86_64/nptl/tls.h
index cf41430050..abfeb88054 100644
--- a/sysdeps/x86_64/nptl/tls.h
+++ b/sysdeps/x86_64/nptl/tls.h
@@ -170,7 +170,7 @@ _Static_assert (offsetof (tcbhead_t, __glibc_unused2) == 0x80,
/* Return the thread descriptor for the current thread. */
# define THREAD_SELF \
- (*(struct pthread *__seg_fs *) offsetof (struct pthread, header.self))
+ (*(struct pthread *__seg_fs *)&((struct pthread __seg_fs *)0)->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. */
@@ -203,8 +203,7 @@ _Static_assert (offsetof (tcbhead_t, __glibc_unused2) == 0x80,
{ int __res; \
asm volatile ("xchgl %1, %0" \
: "=r" (__res) \
- : "m" (*(int __seg_fs *) \
- offsetof (struct pthread, header.gscope_flag)), \
+ : "m" (((struct pthread __seg_fs *)0)->header.gscope_flag), \
"0" (THREAD_GSCOPE_FLAG_UNUSED)); \
if (__res == THREAD_GSCOPE_FLAG_WAIT) \
lll_futex_wake (&THREAD_SELF->header.gscope_flag, 1, LLL_PRIVATE); \
--
2.51.0
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