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authorJeff Dike <jdike@addtoit.com>2006-09-27 04:50:40 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-09-27 11:26:16 -0400
commit3c9173509985b957bea692ea887a8a0e5055cfe8 (patch)
tree9406fb650d6085f992b6d2a0a3fd8763b045cc35 /include/asm-um
parent0915ee38c7db57ff41a7a68bcc02d0dd3b7b849b (diff)
[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>
Diffstat (limited to 'include/asm-um')
-rw-r--r--include/asm-um/processor-generic.h6
1 files changed, 3 insertions, 3 deletions
diff --git a/include/asm-um/processor-generic.h b/include/asm-um/processor-generic.h
index afa4fe1ca9f1..d99bbddffdb9 100644
--- a/include/asm-um/processor-generic.h
+++ b/include/asm-um/processor-generic.h
@@ -13,6 +13,7 @@ struct task_struct;
13#include "asm/ptrace.h" 13#include "asm/ptrace.h"
14#include "choose-mode.h" 14#include "choose-mode.h"
15#include "registers.h" 15#include "registers.h"
16#include "sysdep/archsetjmp.h"
16 17
17struct mm_struct; 18struct mm_struct;
18 19
@@ -43,8 +44,7 @@ struct thread_struct {
43#endif 44#endif
44#ifdef CONFIG_MODE_SKAS 45#ifdef CONFIG_MODE_SKAS
45 struct { 46 struct {
46 void *switch_buf; 47 jmp_buf switch_buf;
47 void *fork_buf;
48 int mm_count; 48 int mm_count;
49 } skas; 49 } skas;
50#endif 50#endif
@@ -138,7 +138,7 @@ extern struct cpuinfo_um cpu_data[];
138 138
139#ifdef CONFIG_MODE_SKAS 139#ifdef CONFIG_MODE_SKAS
140#define KSTK_REG(tsk, reg) \ 140#define KSTK_REG(tsk, reg) \
141 get_thread_reg(reg, tsk->thread.mode.skas.switch_buf) 141 get_thread_reg(reg, &tsk->thread.mode.skas.switch_buf)
142#else 142#else
143#define KSTK_REG(tsk, reg) (0xbadbabe) 143#define KSTK_REG(tsk, reg) (0xbadbabe)
144#endif 144#endif