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authorJeff Dike <jdike@addtoit.com>2005-11-22 00:32:04 -0500
committerLinus Torvalds <torvalds@g5.osdl.org>2005-11-22 12:13:41 -0500
commit39d730ab87f07592e3a3794353f097d5184cae7a (patch)
tree36cb363e0815cb7508227a5063a677fe95e0fa4b /arch/um/kernel
parent18317ab0ca5ac0c654be3eac31ebb781b4a5e9b2 (diff)
[PATCH] uml: eliminate use of local in clone stub
We have a bug in the i386 stub_syscall6 which pushes ebp before the system call and pops it afterwards. Because we use syscall6 to remap the stack, the old contents of the stack (and the former value of ebp) are no longer available. Some versions of gcc make from a real local, accessed through ebp, despite my efforts to make it obvious that references to from are really constants. This patch attempts to make it even more obvious by eliminating from and using a macro to access the stub's data explicitly with constants. My original thinking on this was to replace syscall6 with a remap_stack interface which saved ebp someplace and restored it afterwards. The problem is that there are no registers to put it in, except for esp. That could work, since we can store a constant in esp after the mmap because we just replaced the stack. However, this approach seems a tad cleaner. Signed-off-by: Jeff Dike <jdike@addtoit.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'arch/um/kernel')
-rw-r--r--arch/um/kernel/skas/clone.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/arch/um/kernel/skas/clone.c b/arch/um/kernel/skas/clone.c
index 4dc55f10cd18..39c0d7145d31 100644
--- a/arch/um/kernel/skas/clone.c
+++ b/arch/um/kernel/skas/clone.c
@@ -13,11 +13,13 @@
13/* This is in a separate file because it needs to be compiled with any 13/* This is in a separate file because it needs to be compiled with any
14 * extraneous gcc flags (-pg, -fprofile-arcs, -ftest-coverage) disabled 14 * extraneous gcc flags (-pg, -fprofile-arcs, -ftest-coverage) disabled
15 */ 15 */
16
17#define STUB_DATA(field) (((struct stub_data *) UML_CONFIG_STUB_DATA)->field)
18
16void __attribute__ ((__section__ (".__syscall_stub"))) 19void __attribute__ ((__section__ (".__syscall_stub")))
17stub_clone_handler(void) 20stub_clone_handler(void)
18{ 21{
19 long err; 22 long err;
20 struct stub_data *from = (struct stub_data *) UML_CONFIG_STUB_DATA;
21 23
22 err = stub_syscall2(__NR_clone, CLONE_PARENT | CLONE_FILES | SIGCHLD, 24 err = stub_syscall2(__NR_clone, CLONE_PARENT | CLONE_FILES | SIGCHLD,
23 UML_CONFIG_STUB_DATA + PAGE_SIZE / 2 - 25 UML_CONFIG_STUB_DATA + PAGE_SIZE / 2 -
@@ -30,15 +32,15 @@ stub_clone_handler(void)
30 goto out; 32 goto out;
31 33
32 err = stub_syscall3(__NR_setitimer, ITIMER_VIRTUAL, 34 err = stub_syscall3(__NR_setitimer, ITIMER_VIRTUAL,
33 (long) &from->timer, 0); 35 (long) &STUB_DATA(timer), 0);
34 if(err) 36 if(err)
35 goto out; 37 goto out;
36 38
37 err = stub_syscall6(STUB_MMAP_NR, UML_CONFIG_STUB_DATA, PAGE_SIZE, 39 err = stub_syscall6(STUB_MMAP_NR, UML_CONFIG_STUB_DATA, PAGE_SIZE,
38 PROT_READ | PROT_WRITE, MAP_FIXED | MAP_SHARED, 40 PROT_READ | PROT_WRITE, MAP_FIXED | MAP_SHARED,
39 from->fd, from->offset); 41 STUB_DATA(fd), STUB_DATA(offset));
40 out: 42 out:
41 /* save current result. Parent: pid; child: retcode of mmap */ 43 /* save current result. Parent: pid; child: retcode of mmap */
42 from->err = err; 44 STUB_DATA(err) = err;
43 trap_myself(); 45 trap_myself();
44} 46}