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

[Warner Losh <imp@bsdimp.com>]

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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
>
>

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