guard area suggestion
Ian Wienand <[email protected]>
| Newsgroups | gmane.comp.lib.phil |
|---|---|
| Message-ID | <[email protected]> |
Hello, Attached for consideration is a patch that creates a pointer to the guard area, rather than making the tacit assumption that it will always be at the bottom of the stack. I think it makes it slightly clearer what is happening when you have multiple stacks. Also the stack top gets set to (pd)-1 near the end which I think is incorrect. when the memory is allocated for the stack previously pd is set correctly so this just wastes space. -i [email protected] http://www.gelato.unsw.edu.au
guard.diff
(text/plain, 3.3 KB)
diff -ru ../libc-cvs-orig/nptl/allocatestack.c ./nptl/allocatestack.c
--- ../libc-cvs-orig/nptl/allocatestack.c 2003-03-12 05:02:17.000000000 +1100
+++ ./nptl/allocatestack.c 2003-03-13 12:09:32.000000000 +1100
@@ -350,6 +350,7 @@
size_t guardsize;
size_t reqsize;
void *mem;
+ void *guardptr=NULL; /* initalise to stop gcc warning */
#if COLORING_INCREMENT != 0
/* Add one more page for stack coloring. Don't to it for stacks
@@ -423,6 +424,15 @@
pd->stackblock = mem;
pd->stackblock_size = size;
+#ifdef NEED_SEPARATE_REGISTER_STACK
+ /* the guard area is more or less half way between the top
+ of the stack and the bottom */
+ guardptr = mem + (((size - __static_tls_size - guardsize) / 2) & ~pagesize_m1);
+#else
+ /* the guard area is just at the bottom (mem) */
+ guardptr = mem;
+#endif
+
/* We allocated the first block thread-specific data array.
This address will not change for the lifetime of this
descriptor. */
@@ -478,12 +488,8 @@
/* Create or resize the guard area if necessary. */
if (__builtin_expect (guardsize > pd->guardsize, 0))
{
-#ifdef NEED_SEPARATE_REGISTER_STACK
- char *guard = mem + (((size - guardsize) / 2) & ~pagesize_m1);
-#else
- char *guard = mem;
-#endif
- if (mprotect (guard, guardsize, PROT_NONE) != 0)
+
+ if (mprotect (guardptr, guardsize, PROT_NONE) != 0)
{
int err;
mprot_error:
@@ -510,32 +516,19 @@
}
pd->guardsize = guardsize;
+ pd->guardptr = guardptr;
}
else if (__builtin_expect (pd->guardsize - guardsize > size - reqsize,
0))
{
- /* The old guard area is too large. */
-
-#ifdef NEED_SEPARATE_REGISTER_STACK
- char *guard = mem + (((size - guardsize) / 2) & ~pagesize_m1);
- char *oldguard = mem + (((size - pd->guardsize) / 2) & ~pagesize_m1);
-
- if (oldguard < guard
- && mprotect (oldguard, guard - oldguard,
- PROT_READ | PROT_WRITE | PROT_EXEC) != 0)
- goto mprot_error;
-
- if (mprotect (guard + guardsize,
- oldguard + pd->guardsize - guard - guardsize,
+ /* The old guard area is too large, give permissions back to
+ the extra area. */
+ if (mprotect ((char *) pd->guardptr + guardsize, pd->guardsize - guardsize,
PROT_READ | PROT_WRITE | PROT_EXEC) != 0)
goto mprot_error;
-#else
- if (mprotect ((char *) mem + guardsize, pd->guardsize - guardsize,
- PROT_READ | PROT_WRITE | PROT_EXEC) != 0)
- goto mprot_error;
-#endif
pd->guardsize = guardsize;
+ pd->guardptr = guardptr;
}
}
@@ -546,7 +539,8 @@
/* The stack begins before the TCB and the static TLS block. */
stacktop = ((char *) (pd + 1) - __static_tls_size);
#elif TLS_DTV_AT_TP
- stacktop = (char *) (pd - 1);
+ /* The stack grows from below pd */
+ stacktop = (char *) (pd);
#endif
#ifdef NEED_SEPARATE_REGISTER_STACK
diff -ru ../libc-cvs-orig/nptl/descr.h ./nptl/descr.h
--- ../libc-cvs-orig/nptl/descr.h 2003-03-11 04:33:29.000000000 +1100
+++ ./nptl/descr.h 2003-03-13 12:38:14.000000000 +1100
@@ -179,6 +179,9 @@
size_t stackblock_size;
/* Size of the included guard area. */
size_t guardsize;
+ /* This points to the guard page. Useful for archs with multiple stacks where
+ the guard page might be in the middle of the stack */
+ void *guardptr;
} __attribute ((aligned (TCB_ALIGNMENT)));