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authorRich Felker <dalias@aerifal.cx>2015-11-02 16:37:51 -0500
committerRich Felker <dalias@aerifal.cx>2015-11-02 16:37:51 -0500
commitfda365a53074f97f3213caefe70ea13297acecb2 (patch)
tree2506ac8bfc363f5671a2be0c16a0a69c23167fdf /src/mman/mremap.c
parentf9ecb6bfa1dc9f93a10dad97a158e6b8334c586c (diff)
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fix mremap memory synchronization and use of variadic argument
since mremap with the MREMAP_FIXED flag is an operation that unmaps
existing mappings, it needs to use the vm lock mechanism to ensure
that any in-progress synchronization operations using vm identities
from before the call have finished.

also, the variadic argument was erroneously being read even if the
MREMAP_FIXED flag was not passed. in practice this didn't break
anything, but it's UB and in theory LTO could turn it into a hard
error.
Diffstat (limited to 'src/mman/mremap.c')
-rw-r--r--src/mman/mremap.c15
1 files changed, 11 insertions, 4 deletions
diff --git a/src/mman/mremap.c b/src/mman/mremap.c
index 1096ace1..ce4e8ea1 100644
--- a/src/mman/mremap.c
+++ b/src/mman/mremap.c
@@ -1,3 +1,4 @@
+#define _GNU_SOURCE
 #include <unistd.h>
 #include <sys/mman.h>
 #include <errno.h>
@@ -6,19 +7,25 @@
 #include "syscall.h"
 #include "libc.h"
 
+static void dummy(void) { }
+weak_alias(dummy, __vm_wait);
+
 void *__mremap(void *old_addr, size_t old_len, size_t new_len, int flags, ...)
 {
 	va_list ap;
-	void *new_addr;
+	void *new_addr = 0;
 
 	if (new_len >= PTRDIFF_MAX) {
 		errno = ENOMEM;
 		return MAP_FAILED;
 	}
 
-	va_start(ap, flags);
-	new_addr = va_arg(ap, void *);
-	va_end(ap);
+	if (flags & MREMAP_FIXED) {
+		__vm_wait();
+		va_start(ap, flags);
+		new_addr = va_arg(ap, void *);
+		va_end(ap);
+	}
 
 	return (void *)syscall(SYS_mremap, old_addr, old_len, new_len, flags, new_addr);
 }