Add test/mremap.c, using MREMAP_FIXED

gc00 · gc00 · commit dec266fdf111 · 2025-11-14T01:48:32.000-05:00
diff --git a/src/mtcp/mtcp_restart.c b/src/mtcp/mtcp_restart.c
@@ -647,7 +647,8 @@ compute_regions_to_munmap(RestoreInfo *rinfo)
 
 NO_OPTIMIZE
 static void
-restore_vdso_vvar_work(MemRegion *currentRegion, MemRegion *ckptRegion, const char *regionName)
+restore_vdso_vvar_work(MemRegion *currentRegion, MemRegion *ckptRegion,
+                       const char *regionName)
 {
   int mtcp_sys_errno;
 
@@ -677,7 +678,8 @@ restore_vdso_vvar(RestoreInfo *rinfo)
 {
   restore_vdso_vvar_work(&rinfo->currentVdso, &rinfo->ckptHdr.vdso, "[vdso]");
   restore_vdso_vvar_work(&rinfo->currentVvar, &rinfo->ckptHdr.vvar, "[vvar]");
-  restore_vdso_vvar_work(&rinfo->currentVvarVClock, &rinfo->ckptHdr.vvarVClock, "[vvar_vclock]");
+  restore_vdso_vvar_work(&rinfo->currentVvarVClock, &rinfo->ckptHdr.vvarVClock,
+                         "[vvar_vclock]");
 
   if (rinfo->currentVdso.startAddr != 0) {
     mtcp_setauxval(rinfo->environ, AT_SYSINFO_EHDR,
@@ -967,9 +969,9 @@ doAreasOverlap(Area *area, MemRegion *memRegion)
 }
 
 /* This uses MREMAP_FIXED | MREMAP_MAYMOVE to move a memory segment.
- * Note that we need 'MREMAP_MAYMOVE'.  With only 'MREMAP_FIXED', the
- * kernel can overwrite an existing memory region.
- * Note that 'mremap' and hence 'mremap_move' do not allow overlapping src and dest.
+ * Note that 'MREMAP_MAYMOVE' is required, if using 'MREMAP_FIXED'.
+ * Note that 'mremap' and hence 'mremap_move' do not allow overlapping
+ *   src and dest.
  */
 NO_OPTIMIZE
 static int
@@ -987,7 +989,7 @@ mremap_move(void *dest, void *src, size_t size) {
     return -1; // Error
   } else {
     // Else 'MREMAP_MAYMOVE' forced the remap to the wrong location.  So, the
-    // memory was moved to the wrong desgination.  Undo the move, and return -1.
+    // memory was moved to the wrong destination.  Undo the move, and return -1.
     mremap_move(src, rc, size);
     return -1; // Error
   }
diff --git a/test/autotest.py b/test/autotest.py
@@ -897,6 +897,8 @@ def saveResultsNMI():
 
 runTest("mmap1", 1, ["./test/mmap1"])
 
+runTest("mremap", 1, ["./test/mremap"])
+
 if HAS_SELINUX == "yes":
   runTest("selinux1", 1, ["./test/selinux1"])
 
diff --git a/test/mremap.c b/test/mremap.c
@@ -0,0 +1,23 @@
+#define _GNU_SOURCE
+#include <assert.h>
+#include <unistd.h>
+#include <sys/mman.h>
+
+int main() {
+    long page_size = sysconf(_SC_PAGESIZE);
+    void *old_addr1, *old_addr2, *new_addr;
+    while (1) {
+      old_addr1 = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+                       MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+      old_addr2 = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+                       MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+      munmap(old_addr2, page_size);
+      // We now know that old_addr1 is mapped and old_addr2 is not mapped.
+      new_addr = mremap(old_addr1, page_size, page_size,
+                        MREMAP_MAYMOVE | MREMAP_FIXED, old_addr2);
+      assert (new_addr == old_addr2);
+      munmap(old_addr2, page_size);
+      sleep(1);
+    }
+    return 0;
+}
