Re: [Qemu-devel] [PATCH v1 5/5] linux-user/elfload: Fix GCC 9 build warnings

[Alistair Francis]

On Tue, Apr 30, 2019 at 2:10 PM Eric Blake <address@hidden> wrote:
>
> On 4/30/19 4:01 PM, Alistair Francis wrote:
> > On Tue, Apr 30, 2019 at 1:36 PM Laurent Vivier <address@hidden> wrote:
> >>
> >> Le 30/04/2019 à 22:09, Alistair Francis a écrit :
> >>> Fix this warning when building with GCC9 on Fedora 30:
> >>> In function ‘strncpy’,
> >>>     inlined from ‘fill_psinfo’ at 
> >>> /home/alistair/qemu/linux-user/elfload.c:3208:12,
> >>>     inlined from ‘fill_note_info’ at 
> >>> /home/alistair/qemu/linux-user/elfload.c:3390:5,
> >>>     inlined from ‘elf_core_dump’ at 
> >>> /home/alistair/qemu/linux-user/elfload.c:3539:9:
> >>> /usr/include/bits/string_fortified.h:106:10: error: ‘__builtin_strncpy’ 
> >>> specified bound 16 equals destination size [-Werror=stringop-truncation]
> >>>   106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos 
> >>> (__dest));
> >>>       |          
> >>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >>>
>
> >>        /*
> >>         * Using strncpy here is fine: at max-length,
> >>>       * this field is not NUL-terminated.
> >>>       */>      (void) strncpy(psinfo->pr_fname, base_filename,
> >>> -                   sizeof(psinfo->pr_fname));
> >>> +                   sizeof(psinfo->pr_fname) - 1);
> >>
> >> Read the comment above :)
> >
> > GCC can't read the comment though. The only other option I can think
> > of is using a pragma, which I avoided using unless I had to. Would you
> > prefer a pragma here? Or do you have a better solution?
>
> psinfo is struct target_elf_prpsinfo, which we declare.  Why not just
> use the QEMU_NONSTRING attribute in the declaration, to tell the
> compiler our exact intents (untested, but something like this):
>
> diff --git i/linux-user/elfload.c w/linux-user/elfload.c
> index c1a26021f8d..6ebb2eeb957 100644
> --- i/linux-user/elfload.c
> +++ w/linux-user/elfload.c
> @@ -2872,7 +2872,7 @@ struct target_elf_prpsinfo {
>      target_gid_t pr_gid;
>      target_pid_t pr_pid, pr_ppid, pr_pgrp, pr_sid;
>      /* Lots missing */
> -    char    pr_fname[16];           /* filename of executable */
> +    char    pr_fname[16] QEMU_NONSTRING;           /* filename of
> executable */
>      char    pr_psargs[ELF_PRARGSZ]; /* initial part of arg list */
>  };

I didn't know about that property, that fixes it.

Alistair

>
>
>
>
> --
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3226
> Virtualization:  qemu.org | libvirt.org
>