linux-user: fix statfs

The statfs syscall should always memset(0) its full struct extent before
writing to it. Newer versions of the syscall use one of the reserved fields
for flags, which would otherwise get stale values from uncleaned memory.

This fixes libarchive for me, which got confused about the return value of
pathconf("/", _PC_REC_XFER_ALIGN) otherwise, as it some times gave old pointers
as return value.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>

linux-user/syscall.c

@@ -6529,6 +6529,8 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
             __put_user(stfs.f_fsid.__val[0], &target_stfs->f_fsid.val[0]);
             __put_user(stfs.f_fsid.__val[1], &target_stfs->f_fsid.val[1]);
             __put_user(stfs.f_namelen, &target_stfs->f_namelen);
+            __put_user(stfs.f_frsize, &target_stfs->f_frsize);
+            memset(target_stfs->f_spare, 0, sizeof(target_stfs->f_spare));
             unlock_user_struct(target_stfs, arg2, 1);
         }
         break;
@@ -6557,6 +6559,8 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
             __put_user(stfs.f_fsid.__val[0], &target_stfs->f_fsid.val[0]);
             __put_user(stfs.f_fsid.__val[1], &target_stfs->f_fsid.val[1]);
             __put_user(stfs.f_namelen, &target_stfs->f_namelen);
+            __put_user(stfs.f_frsize, &target_stfs->f_frsize);
+            memset(target_stfs->f_spare, 0, sizeof(target_stfs->f_spare));
             unlock_user_struct(target_stfs, arg3, 1);
         }
         break;