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Re: [Qemu-devel] [PATCH v1 4/5] linux-user/uname: Fix GCC 9 build warnin
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH v1 4/5] linux-user/uname: Fix GCC 9 build warnings |
Date: |
Tue, 30 Apr 2019 15:40:10 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 |
On 4/30/19 3:09 PM, Alistair Francis wrote:
> Fix this warning when building with GCC9 on Fedora 30:
> In function ‘strncpy’,
> inlined from ‘sys_uname’ at /home/alistair/qemu/linux-user/uname.c:94:3:
> /usr/include/bits/string_fortified.h:106:10: error: ‘__builtin_strncpy’
> output may be truncated copying 64 bytes from a string of length 64
> [-Werror=stringop-truncation]
> 106 | return __builtin___strncpy_chk (__dest, __src, __len, __bos
> (__dest));
> |
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Signed-off-by: Alistair Francis <address@hidden>
> ---
> linux-user/uname.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/linux-user/uname.c b/linux-user/uname.c
> index 313b79dbad..293b2238f2 100644
> --- a/linux-user/uname.c
> +++ b/linux-user/uname.c
> @@ -90,6 +90,11 @@ int sys_uname(struct new_utsname *buf)
> * struct linux kernel uses).
> */
>
> +#if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && QEMU_GNUC_PREREQ(9, 0)
> +#pragma GCC diagnostic push
> +#pragma GCC diagnostic ignored "-Wstringop-truncation"
> +#endif
Why do we need the pragma?
> +
> memset(buf, 0, sizeof(*buf));
We are prezeroing the entire field, at which point...
> COPY_UTSNAME_FIELD(buf->sysname, uts_buf.sysname);
> COPY_UTSNAME_FIELD(buf->nodename, uts_buf.nodename);
...using strncpy() for a shorter string is wasteful (we're writing the
tail end twice), and for a long string is warning-prone. Why not
rewrite COPY_UTSNAME_FIELD() to use memcpy() for the MIN(strlen(src),
__NEW_UTS_LEN) and drop the write of the trailing NUL, since it will
already be NUL from your memset()?
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
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- Re: [Qemu-devel] [PATCH v1 2/5] hw/usb/hcd-xhci: Fix GCC 9 build warning, (continued)