On 03/17/2015 07:07 PM, Peter Maydell wrote:
On 17 March 2015 at 19:59, John Snow <js...@redhat.com> wrote:
On 03/17/2015 03:34 PM, Peter Maydell wrote:
On 17 March 2015 at 19:30, John Snow <js...@redhat.com> wrote:
-Wunused-command-line-argument currently complains about the
many include flags passed to each CC incantation
Do you see this with really just --cc=clang ? I see these warnings
if I try to use clang with ccache, but I believe that's a ccache bug.
Not /intentionally/ invoking ccache:
../../configure --cc=clang --host-cc=clang --enable-debug
--extra-cflags="-Werror -Wno-unknown-attributes -Wno-parentheses-equality
-Wno-self-assign -Wno-tautological-compare"
But that's because:
which clang
/usr/lib64/ccache/clang
Which is definitely not of my own doing -- seems to be a default in Fedora
21.
Brave of them :-)
Supposedly this bug is fixed in ccache 3.2:
https://bugzilla.samba.org/show_bug.cgi?id=8118
You can probably work around it by telling QEMU's configure
--extra-cflags=-Qunused-arguments or something similar.
-- PMM
Ah, yes; many of these wind up being ccache problems, but not all of them.
There's one case of error here that's interesting that ccache unearths:
we use a gnu extension to give return values to compound statement
blocks, then wrap these blocks into macros as if they were functions.
The practical outcome here is that these blocks have return codes that
we often don't check, so clang will spit out "unused value" warnings if
we compile these after preprocessing, like ccache will tend to do.
This warning is potentially valid: if these calls can fail, we should
probably either be asserting that a failure did not occur OR we should
switch to a variant without a return code, if failure is impossible in
these locations.
An example of this is in linux-user/elfload.c where we define the
NEW_AUX_ENT() macro which in turn uses the put_user_ual(val, sp) macro.
When this is expanded, it turns into a compound statement where we
discard the expression result, so clang whines.
Of course, this all goes away if you disable ccache, but is it worth
adjusting this particular usage anyway?
--js
