Commit 2b647a95 authored by David Schleef's avatar David Schleef

Cleaned up cothread_create(), added comments, added code to unmap a guard page.

Original commit message from CVS:
Cleaned up cothread_create(), added comments, added code to unmap a
guard page.
parent 926f38ba
......@@ -133,7 +133,7 @@ cothread_context_init (void)
/* FIXME: an assumption is made that the stack segment is STACK_SIZE
* aligned. */
ctx->stack_top = ((gulong) sp | (STACK_SIZE - 1)) + 1;
GST_DEBUG (GST_CAT_COTHREADS, "stack top is %lu", ctx->stack_top);
GST_DEBUG (GST_CAT_COTHREADS, "stack top is 0x%08lx", ctx->stack_top);
/*
* initialize the 0th cothread
......@@ -193,11 +193,9 @@ cothread_state*
cothread_create (cothread_context *ctx)
{
cothread_state *cothread;
//void *sp;
//unsigned long stack_top;
void *mmaped = 0;
gint slot = 0;
unsigned long page_size;
g_return_val_if_fail (ctx != NULL, NULL);
......@@ -219,35 +217,28 @@ cothread_create (cothread_context *ctx)
GST_DEBUG (GST_CAT_COTHREADS, "Found free cothread slot %d", slot);
#if 0
sp = CURRENT_STACK_FRAME;
/* FIXME this may not be 64bit clean
* could use casts to uintptr_t from inttypes.h
* if only all platforms had inttypes.h
*/
/* stack_top is the address of the first byte past our stack segment. */
/* FIXME: an assumption is made that the stack segment is STACK_SIZE
* aligned. */
stack_top = ((gulong) sp | (STACK_SIZE - 1)) + 1;
GST_DEBUG (GST_CAT_COTHREADS, "stack top is 0x%lx", stack_top);
#endif
/* cothread stack space of the thread is mapped in reverse, with cothread 0
* stack space at the top */
cothread = (cothread_state *) (ctx->stack_top - (slot + 1) * COTHREAD_STACKSIZE);
GST_DEBUG (GST_CAT_COTHREADS, "cothread pointer is %p", cothread);
#if 0
/* This tests to see whether or not we can grow down the stack */
{
unsigned long ptr;
for(ptr=ctx->stack_top - 4096; ptr > (unsigned long)cothread; ptr -= 4096){
GST_DEBUG (GST_CAT_COTHREADS, "touching location 0x%08lx", ptr);
*(volatile unsigned int *)ptr = *(volatile unsigned int *)ptr;
GST_DEBUG (GST_CAT_COTHREADS, "ok (0x%08x)", *(unsigned int *)ptr);
}
}
#endif
GST_DEBUG (GST_CAT_COTHREADS,
"mmap cothread slot stack from %p to 0x%lx (size 0x%lx)",
cothread, (unsigned long) cothread + COTHREAD_STACKSIZE,
(long) COTHREAD_STACKSIZE);
GST_DEBUG (GST_CAT_COTHREADS, "going into mmap");
/* the mmap is used to reserve part of the stack
* ie. we state explicitly that we are going to use it */
/* FIXME: maybe we should map slightly less than COTHREAD_STACKSIZE,
* so that stack overruns possibly could segfault ? */
mmaped = mmap ((void *) (cothread),
COTHREAD_STACKSIZE,
/* The mmap is necessary on Linux/i386, and possibly others, since the
* kernel is picky about when we can expand our stack. */
GST_DEBUG (GST_CAT_COTHREADS, "mmaping %p, size 0x%08x", cothread,
COTHREAD_STACKSIZE);
mmaped = mmap ((void *) cothread, COTHREAD_STACKSIZE,
PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
GST_DEBUG (GST_CAT_COTHREADS, "coming out of mmap");
......@@ -260,6 +251,16 @@ cothread_create (cothread_context *ctx)
return NULL;
}
#ifdef _SC_PAGESIZE
page_size = sysconf(_SC_PAGESIZE);
#else
page_size = getpagesize();
#endif
/* Unmap a guard page. This decreases our stack size by 8 kB (for
* 4 kB pages) and also wastes almost 4 kB for the cothreads
* structure */
munmap((void *)cothread + page_size, page_size);
cothread->magic_number = COTHREAD_MAGIC_NUMBER;
GST_DEBUG (GST_CAT_COTHREADS, "create cothread %d with magic number 0x%x",
slot, cothread->magic_number);
......@@ -268,6 +269,7 @@ cothread_create (cothread_context *ctx)
cothread->flags = 0;
cothread->priv = NULL;
cothread->sp = ((guchar *) cothread + COTHREAD_STACKSIZE);
cothread->sp -= 16; /* necessary for PowerPC */
cothread->top_sp = cothread->sp; /* for debugging purposes
to detect stack overruns */
......
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