Fix brk/sbrk error checking.
Note that the kernel returns the current break on error or if the requested
break is smaller than the minimum break, or the new break. I don't know where
we got the idea that the kernel could return -1.
Also optimizes the query case.
Also hides an accidentally-exported symbol for LP64.
Change-Id: I0fd6b8b14ddf1ae82935c0c3fc610da5cc74932e
diff --git a/libc/bionic/brk.cpp b/libc/bionic/brk.cpp
index 633b914..4d08a61 100644
--- a/libc/bionic/brk.cpp
+++ b/libc/bionic/brk.cpp
@@ -26,16 +26,49 @@
* SUCH DAMAGE.
*/
+#include <errno.h>
#include <unistd.h>
-/* Shared with sbrk.c. */
-extern "C" void* __bionic_brk; // TODO: should be __LIBC_HIDDEN__ but accidentally exported by NDK :-(
+#if __LP64__
+static void* __bionic_brk;
+#else
+void* __bionic_brk; // Accidentally exported by the NDK.
+#endif
int brk(void* end_data) {
- void* new_brk = __brk(end_data);
- if (new_brk != end_data) {
+ __bionic_brk = __brk(end_data);
+ if (__bionic_brk < end_data) {
+ errno = ENOMEM;
return -1;
}
- __bionic_brk = new_brk;
return 0;
}
+
+void* sbrk(ptrdiff_t increment) {
+ // Initialize __bionic_brk if necessary.
+ if (__bionic_brk == NULL) {
+ __bionic_brk = __brk(NULL);
+ }
+
+ // Don't ask the kernel if we already know the answer.
+ if (increment == 0) {
+ return __bionic_brk;
+ }
+
+ // Avoid overflow.
+ intptr_t old_brk = reinterpret_cast<intptr_t>(__bionic_brk);
+ if ((increment > 0 && INTPTR_MAX - increment > old_brk) ||
+ (increment < 0 && (increment == PTRDIFF_MIN || old_brk < -increment))) {
+ errno = ENOMEM;
+ return reinterpret_cast<void*>(-1);
+ }
+
+ void* desired_brk = reinterpret_cast<void*>(old_brk + increment);
+ __bionic_brk = __brk(desired_brk);
+
+ if (__bionic_brk < desired_brk) {
+ errno = ENOMEM;
+ return reinterpret_cast<void*>(-1);
+ }
+ return reinterpret_cast<void*>(old_brk);
+}