[Qemu-devel] [PATCH 5/6] linux-user: Allocate the right amount of space for non-fixed file maps

[Richard Henderson <rth@twiddle.net>]

If we let the kernel handle the implementation of mmap_find_vma,
via an anon mmap, we must use the size as indicated by the user
and not the size truncated to the filesize.

This happens often in ld.so, where we initially mmap the file to
the size of the text+data+bss to reserve an area, then mmap+fixed
over the top to properly handle data and bss.

Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 linux-user/mmap.c |   30 +++++++++++++++++++-----------
 1 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index d9468fe..b412e3f 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -382,7 +382,6 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
                      int flags, int fd, abi_ulong offset)
 {
     abi_ulong ret, end, real_start, real_end, retaddr, host_offset, host_len;
-    unsigned long host_start;
 
     mmap_lock();
 #ifdef DEBUG_MMAP
@@ -421,6 +420,19 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
     if (len == 0)
         goto the_end;
     real_start = start & qemu_host_page_mask;
+    host_offset = offset & qemu_host_page_mask;
+
+    /* If the user is asking for the kernel to find a location, do that
+       before we truncate the length for mapping files below.  */
+    if (!(flags & MAP_FIXED)) {
+        host_len = len + offset - host_offset;
+        host_len = HOST_PAGE_ALIGN(host_len);
+        start = mmap_find_vma(real_start, host_len);
+        if (start == (abi_ulong)-1) {
+            errno = ENOMEM;
+            goto fail;
+        }
+    }
 
     /* When mapping files into a memory area larger than the file, accesses
        to pages beyond the file size will cause a SIGBUS. 
@@ -453,27 +465,23 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
     }
 
     if (!(flags & MAP_FIXED)) {
-        abi_ulong mmap_start;
+        unsigned long host_start;
         void *p;
-        host_offset = offset & qemu_host_page_mask;
+
         host_len = len + offset - host_offset;
         host_len = HOST_PAGE_ALIGN(host_len);
-        mmap_start = mmap_find_vma(real_start, host_len);
-        if (mmap_start == (abi_ulong)-1) {
-            errno = ENOMEM;
-            goto fail;
-        }
+
         /* Note: we prefer to control the mapping address. It is
            especially important if qemu_host_page_size >
            qemu_real_host_page_size */
-        p = mmap(g2h(mmap_start),
-                 host_len, prot, flags | MAP_FIXED | MAP_ANONYMOUS, -1, 0);
+        p = mmap(g2h(start), host_len, prot,
+                 flags | MAP_FIXED | MAP_ANONYMOUS, -1, 0);
         if (p == MAP_FAILED)
             goto fail;
         /* update start so that it points to the file position at 'offset' */
         host_start = (unsigned long)p;
         if (!(flags & MAP_ANONYMOUS)) {
-            p = mmap(g2h(mmap_start), len, prot, 
+            p = mmap(g2h(start), len, prot,
                      flags | MAP_FIXED, fd, host_offset);
             host_start += offset - host_offset;
         }
-- 
1.7.7.6