Re: [PATCH v2 4/9] bsd-user/syscall: Replace alloca() by g_new()

[Warner Losh]

On Thu, May 6, 2021, 7:38 AM Philippe Mathieu-Daudé <philmd@redhat.com> wrote:

The ALLOCA(3) man-page mentions its "use is discouraged".

Replace it by a g_new() call.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 bsd-user/syscall.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/bsd-user/syscall.c b/bsd-user/syscall.c
index 4abff796c76..dbee0385ceb 100644
--- a/bsd-user/syscall.c
+++ b/bsd-user/syscall.c
@@ -355,9 +355,8 @@ abi_long do_freebsd_syscall(void *cpu_env, int num, abi_long arg1,
     case TARGET_FREEBSD_NR_writev:
         {
             int count = arg3;
-            struct iovec *vec;
+            g_autofree struct iovec *vec = g_new(struct iovec, count);

Where is this freed? Also, alloca just moves a stack pointer, where malloc has complex interactions. Are you sure that's a safe change here?

Warner

-            vec = alloca(count * sizeof(struct iovec));
             if (lock_iovec(VERIFY_READ, vec, arg2, count, 1) < 0)
                 goto efault;
             ret = get_errno(writev(arg1, vec, count));
--
2.26.3