From 5db951ef80cae8b627f95b995811bf916c069757 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Wed, 31 Jul 2013 15:19:39 -0400 Subject: [PATCH] in pthread_getattr_np, use mremap rather than madvise to measure stack the original motivation for this patch was that qemu (and possibly other syscall emulators) nop out madvise, resulting in an infinite loop. however, there is another benefit to this change: madvise may actually undo an explicit madvise the application intended for its stack, whereas the mremap operation is a true nop. the logic here is that mremap must fail if it cannot resize the mapping in-place, and the caller knows that it cannot resize in-place because it knows the next page of virtual memory is already occupied. --- src/thread/pthread_getattr_np.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/src/thread/pthread_getattr_np.c b/src/thread/pthread_getattr_np.c index 945242b7..86df1def 100644 --- a/src/thread/pthread_getattr_np.c +++ b/src/thread/pthread_getattr_np.c @@ -1,3 +1,4 @@ +#define _GNU_SOURCE #include "pthread_impl.h" #include @@ -13,7 +14,7 @@ int pthread_getattr_np(pthread_t t, pthread_attr_t *a) size_t l = PAGE_SIZE; p += -(uintptr_t)p & PAGE_SIZE-1; a->_a_stackaddr = (uintptr_t)p; - while (!posix_madvise(p-l-PAGE_SIZE, PAGE_SIZE, POSIX_MADV_NORMAL)) + while (mremap(p-l-PAGE_SIZE, PAGE_SIZE, 2*PAGE_SIZE, 0)==MAP_FAILED && errno==ENOMEM) l += PAGE_SIZE; a->_a_stacksize = l - DEFAULT_STACK_SIZE; } -- 2.25.1