Support madvise(MADV_DONTDUMP) when creating core dumps for qemu-user

include/exec/page-protection.h

@@ -38,6 +38,12 @@
  */
 #define PAGE_PASSTHROUGH 0x0800
 
+/*
+ * For linux-user, indicates that the page should not be included in a core
+ * dump.
+ */
+#define PAGE_DONTDUMP   0x1000
+
 #ifdef CONFIG_USER_ONLY
 
 void TSA_NO_TSA mmap_lock(void);

linux-user/elfload.c

@@ -4068,6 +4068,10 @@ static size_t vma_dump_size(target_ulong start, target_ulong end,
         return 0;
     }
 
+    if (flags & PAGE_DONTDUMP) {
+        return 0;
+    }
+
     /*
      * Usually we don't dump executable pages as they contain
      * non-writable code that debugger can read directly from

linux-user/mmap.c

@@ -1246,6 +1246,11 @@ abi_long target_madvise(abi_ulong start, abi_ulong len_in, int advice)
      */
     mmap_lock();
     switch (advice) {
+    case MADV_DONTDUMP:
+        if (len > 0) {
+            page_set_flags(start, start + len - 1, PAGE_DONTDUMP);
+        }
+        break;
     case MADV_WIPEONFORK:
     case MADV_KEEPONFORK:
         ret = -EINVAL;