[PATCH] target/i386/hax-posix: fix two 'format-truncation' compile warnings

[pannengyuan]

From: Pan Nengyuan <address@hidden>

Fix compile warnings:
/mnt/sdb/qemu-new/qemu_test/qemu/target/i386/hax-posix.c:124:56: error: ‘%02d’ 
directive output may be truncated writing between 2 and 11 bytes into a region 
of size 3 [-Werror=format-truncation=]
     snprintf(name, sizeof HAX_VM_DEVFS, "/dev/hax_vm/vm%02d", vm_id);
                                                        ^~~~
/mnt/sdb/qemu-new/qemu_test/qemu/target/i386/hax-posix.c:124:41: note: 
directive argument in the range [-2147483648, 64]
     snprintf(name, sizeof HAX_VM_DEVFS, "/dev/hax_vm/vm%02d", vm_id);
                                         ^~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/stdio.h:873,
                 from /mnt/sdb/qemu-new/qemu_test/qemu/include/qemu/osdep.h:99,
                 from 
/mnt/sdb/qemu-new/qemu_test/qemu/target/i386/hax-posix.c:14:
/usr/include/bits/stdio2.h:67:10: note: ‘__builtin___snprintf_chk’ output 
between 17 and 26 bytes into a destination of size 17
   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        __bos (__s), __fmt, __va_arg_pack ());
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/mnt/sdb/qemu-new/qemu_test/qemu/target/i386/hax-posix.c: In function 
‘hax_vcpu_devfs_string’:
/mnt/sdb/qemu-new/qemu_test/qemu/target/i386/hax-posix.c:143:55: error: ‘%02d’ 
directive output may be truncated writing between 2 and 11 bytes into a region 
of size 10 [-Werror=format-truncation=]
     snprintf(name, sizeof HAX_VCPU_DEVFS, "/dev/hax_vm%02d/vcpu%02d",
                                                       ^~~~
/mnt/sdb/qemu-new/qemu_test/qemu/target/i386/hax-posix.c:143:43: note: 
directive argument in the range [-2147483648, 64]
     snprintf(name, sizeof HAX_VCPU_DEVFS, "/dev/hax_vm%02d/vcpu%02d",
                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~
/mnt/sdb/qemu-new/qemu_test/qemu/target/i386/hax-posix.c:143:43: note: 
directive argument in the range [-2147483648, 64]
In file included from /usr/include/stdio.h:873,
                 from /mnt/sdb/qemu-new/qemu_test/qemu/include/qemu/osdep.h:99,
                 from 
/mnt/sdb/qemu-new/qemu_test/qemu/target/i386/hax-posix.c:14:
/usr/include/bits/stdio2.h:67:10: note: ‘__builtin___snprintf_chk’ output 
between 21 and 39 bytes into a destination of size 21
   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        __bos (__s), __fmt, __va_arg_pack ());

We know that we have checked the vm_id and vcpu_id in the first(less than 
0x40), it will never be truncated in snprintf().
Thus, this patch add an assertion to clear this false-positive warning.

Reported-by: Euler Robot <address@hidden>
Signed-off-by: Pan Nengyuan <address@hidden>
---
 target/i386/hax-posix.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/target/i386/hax-posix.c b/target/i386/hax-posix.c
index a5426a6dac..197d5bc0f9 100644
--- a/target/i386/hax-posix.c
+++ b/target/i386/hax-posix.c
@@ -121,7 +121,8 @@ static char *hax_vm_devfs_string(int vm_id)
         return NULL;
     }
 
-    snprintf(name, sizeof HAX_VM_DEVFS, "/dev/hax_vm/vm%02d", vm_id);
+    int len = snprintf(name, sizeof HAX_VM_DEVFS, "/dev/hax_vm/vm%02d", vm_id);
+    assert(len < sizeof HAX_VM_DEVFS);
     return name;
 }
 
@@ -140,8 +141,9 @@ static char *hax_vcpu_devfs_string(int vm_id, int vcpu_id)
         return NULL;
     }
 
-    snprintf(name, sizeof HAX_VCPU_DEVFS, "/dev/hax_vm%02d/vcpu%02d",
-             vm_id, vcpu_id);
+    int len = snprintf(name, sizeof HAX_VCPU_DEVFS, "/dev/hax_vm%02d/vcpu%02d",
+                       vm_id, vcpu_id);
+    assert(len < sizeof HAX_VCPU_DEVFS);
     return name;
 }
 
-- 
2.18.2