pthread中线程是怎么创建的（2）---glibc到内核

/* We rely heavily on various flags the CLONE function understands:

CLONE_VM, CLONE_FS, CLONE_FILES
These flags select semantics with shared address space and
file descriptors according to what POSIX requires.

CLONE_SIGNAL
This flag selects the POSIX signal semantics.

CLONE_SETTLS
The sixth parameter to CLONE determines the TLS area for the
new thread.

CLONE_PARENT_SETTID
The kernels writes the thread ID of the newly created thread
into the location pointed to by the fifth parameters to CLONE.

Note that it would be semantically equivalent to use
CLONE_CHILD_SETTID but it is be more expensive in the kernel.

CLONE_CHILD_CLEARTID
The kernels clears the thread ID of a thread that has called
sys_exit() in the location pointed to by the seventh parameter
to CLONE.

The termination signal is chosen to be zero which means no signal
is sent. */
int clone_flags = (CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGNAL
| CLONE_SETTLS | CLONE_PARENT_SETTID
| CLONE_CHILD_CLEARTID | CLONE_SYSVSEM
| 0);

int rc = ARCH_CLONE (fct, STACK_VARIABLES_ARGS, clone_flags,
pd, &pd->tid, TLS_VALUE, &pd->tid);

#ifndef ARCH_CLONE
# define ARCH_CLONE __clone
#endif

ENTRY (BP_SYM (__clone))

movl    $SYS_ify(clone),%eax

#define SYS_ify(syscall_name)__NR_##syscall_name

#define __NR_clone 120
#define SYS_clone 120

.long ptregs_sigreturn
.long ptregs_clone /* 120 */
.long sys_setdomainname

#define PTREGSCALL(name) \
ALIGN; \
ptregs_##name: \
leal 4(%esp),%eax; \
jmp sys_##name;

PTREGSCALL(clone)

int sys_clone(struct pt_regs *regs)