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libthread: comment stack border a bit more

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This commit is contained in:
Russ Cox 2020-01-24 13:09:55 -05:00
parent 93e2e820a5
commit 4197af4122
1 changed files with 10 additions and 4 deletions
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14
src/libthread/thread.c
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@ -136,10 +136,16 @@ threadalloc(void (*fn)(void*), void *arg, uint stack)
sysfatal("threadalloc getcontext: %r");
//print("makecontext sp=%p t=%p startfn=%p\n", (char*)t->stk+t->stksize, t, t->startfn);
/* call makecontext to do the real work. */
/* leave a few words open on both ends */
t->context.uc.uc_stack.ss_sp = (void*)(t->stk+8);
t->context.uc.uc_stack.ss_size = t->stksize-64;
/*
* Call makecontext to do the real work.
* To avoid various mistakes on other system software,
* debuggers, and so on, don't get too close to both
* ends of the stack. Just staying away is much easier
* than debugging everything (outside our control)
* that has off-by-one errors.
*/
t->context.uc.uc_stack.ss_sp = (void*)(t->stk+64);
t->context.uc.uc_stack.ss_size = t->stksize-2*64;
#if defined(__sun__) && !defined(__MAKECONTEXT_V2_SOURCE) /* sigh */
/* can avoid this with __MAKECONTEXT_V2_SOURCE but only on SunOS 5.9 */
t->context.uc.uc_stack.ss_sp =