[PATCH] uml: thread creation tidying

fork on UML has always somewhat subtle.  The underlying cause has been the
need to initialize a stack for the new process.  The only portable way to
initialize a new stack is to set it as the alternate signal stack and take a
signal.  The signal handler does whatever initialization is needed and jumps
back to the original stack, where the fork processing is finished.  The basic
context switching mechanism is a jmp_buf for each process.  You switch to a
new process by longjmping to its jmp_buf.

Now that UML has its own implementation of setjmp and longjmp, and I can poke
around inside a jmp_buf without fear that libc will change the structure, a
much simpler mechanism is possible.  The jmpbuf can simply be initialized by
hand.

This eliminates -
	the need to set up and remove the alternate signal stack
	sending and handling a signal
	the signal blocking needed around the stack switching, since
there is no stack switching
	setting up the jmp_buf needed to jump back to the original
stack after the new one is set up

In addition, since jmp_buf is now defined by UML, and not by libc, it can be
embedded in the thread struct.  This makes it unnecessary to have it exist on
the stack, where it used to be.  It also simplifies interfaces, since the
switch jmp_buf used to be a void * inside the thread struct, and functions
which took it as an argument needed to define a jmp_buf variable and assign it
from the void *.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

4 files changed, 11 insertions, 8 deletions

diff --git a/arch/um/include/os.h b/arch/um/include/os.h
index be71b3d4c96..120ca21a513 100644
--- a/arch/um/include/os.h
+++ b/arch/um/include/os.h
@@ -14,6 +14,7 @@
 #include "skas/mm_id.h"
 #include "irq_user.h"
 #include "sysdep/tls.h"
+#include "sysdep/archsetjmp.h"
 
 #define OS_TYPE_FILE 1
 #define OS_TYPE_DIR 2
@@ -308,12 +309,9 @@ extern int copy_context_skas0(unsigned long stack, int pid);
 extern void userspace(union uml_pt_regs *regs);
 extern void map_stub_pages(int fd, unsigned long code,
 			   unsigned long data, unsigned long stack);
-extern void new_thread(void *stack, void **switch_buf_ptr,
-			 void **fork_buf_ptr, void (*handler)(int));
-extern void thread_wait(void *sw, void *fb);
-extern void switch_threads(void *me, void *next);
-extern int start_idle_thread(void *stack, void *switch_buf_ptr,
-			     void **fork_buf_ptr);
+extern void new_thread(void *stack, jmp_buf *buf, void (*handler)(void));
+extern void switch_threads(jmp_buf *me, jmp_buf *you);
+extern int start_idle_thread(void *stack, jmp_buf *switch_buf);
 extern void initial_thread_cb_skas(void (*proc)(void *),
 				 void *arg);
 extern void halt_skas(void);
diff --git a/arch/um/include/skas/skas.h b/arch/um/include/skas/skas.h
index 853b26f148c..e88926b1607 100644
--- a/arch/um/include/skas/skas.h
+++ b/arch/um/include/skas/skas.h
@@ -14,8 +14,7 @@ extern int proc_mm, ptrace_faultinfo, ptrace_ldt;
 extern int skas_needs_stub;
 
 extern int user_thread(unsigned long stack, int flags);
-extern void new_thread_proc(void *stack, void (*handler)(int sig));
-extern void new_thread_handler(int sig);
+extern void new_thread_handler(void);
 extern void handle_syscall(union uml_pt_regs *regs);
 extern int new_mm(unsigned long stack);
 extern void get_skas_faultinfo(int pid, struct faultinfo * fi);
diff --git a/arch/um/include/sysdep-i386/archsetjmp.h b/arch/um/include/sysdep-i386/archsetjmp.h
index ea1ba3d42ae..11bafab669e 100644
--- a/arch/um/include/sysdep-i386/archsetjmp.h
+++ b/arch/um/include/sysdep-i386/archsetjmp.h
@@ -16,4 +16,7 @@ struct __jmp_buf {
 
 typedef struct __jmp_buf jmp_buf[1];
 
+#define JB_IP __eip
+#define JB_SP __esp
+
 #endif				/* _SETJMP_H */
diff --git a/arch/um/include/sysdep-x86_64/archsetjmp.h b/arch/um/include/sysdep-x86_64/archsetjmp.h
index 454fc60aff6..9a5e1a6ec80 100644
--- a/arch/um/include/sysdep-x86_64/archsetjmp.h
+++ b/arch/um/include/sysdep-x86_64/archsetjmp.h
@@ -18,4 +18,7 @@ struct __jmp_buf {
 
 typedef struct __jmp_buf jmp_buf[1];
 
+#define JB_IP __rip
+#define JB_SP __rsp
+
 #endif				/* _SETJMP_H */