[Qemu-devel] [PATCH v2] linux-user/mmap.c: Avoid choosing NULL as start address

[Maximilian Riemensberger]

mmap() is required by the linux kernel ABI and POSIX to return a
non-NULL address when the implementation chooses a start address for the
mapping.

The current implementation of mmap_find_vma_reserved() can return NULL
as start address of a mapping which leads to subsequent crashes inside
the guests glibc, e.g. output of qemu-arm-static --strace executing a
test binary stx_test:

    1879 
mmap2(NULL,8388608,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANONYMOUS|0x20000,-1,0) 
= 0x00000000
    1879 write(2,0xf6fd39d0,79) stx_test: allocatestack.c:514: allocate_stack: 
Assertion `mem != NULL' failed.

This patch fixes mmap_find_vma_reserved() by skipping NULL as start
address while searching for a suitable mapping start address.

CC: Riku Voipio <address@hidden>
CC: Laurent Vivier <address@hidden>
CC: Peter Maydell <address@hidden>
Signed-off-by: Maximilian Riemensberger <address@hidden>
---
Changes since v1:
    - Applied feedback from Laurent Vivier

 linux-user/mmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index 4888f53..0fbfd6d 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -234,7 +234,7 @@ static abi_ulong mmap_find_vma_reserved(abi_ulong start, 
abi_ulong size)
         if (prot) {
             end_addr = addr;
         }
-        if (addr + size == end_addr) {
+        if (addr && addr + size == end_addr) {
             break;
         }
         addr -= qemu_host_page_size;
-- 
2.7.4