Le 30/04/2019 à 22:40, Eric Blake a écrit : > 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 <alistair.fran...@wdc.com> >> --- >> 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()? >
We must modify this very carefully because I think there is some magic
in COPY_UTSNAME_FIELD() we could miss.
#define COPY_UTSNAME_FIELD(dest, src) \
do { \
/* __NEW_UTS_LEN doesn't include terminating null */ \
(void) strncpy((dest), (src), __NEW_UTS_LEN); \
(dest)[__NEW_UTS_LEN] = '\0'; \
} while (0)
Thanks,
Laurent
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