Re: [Qemu-devel] [PATCH] Makefile: Don't build generated headers before Makefile is reread

[Peter Maydell]

On 4 July 2014 15:33, Peter Maydell <address@hidden> wrote:
> On 30 June 2014 13:09, Paolo Bonzini <address@hidden> wrote:
>> Il 28/06/2014 18:59, Peter Maydell ha scritto:
>>
>>> Having a direct dependency
>>>    Makefile: $(GENERATED_HEADERS)
>>> can result in not-from-clean builds failing sometimes, because it means
>>> that when Make does its "is any makefile or include out of date and
>>> needing a rebuild?" check, as well as possibly running configure (to
>>> update config-host.mak) it will also rebuild GENERATED_HEADERS under
>>> the "old" config-host.mak regime. If the makefile rules for rebuilding
>>> the generated headers have changed in a way that means they're not
>>> compatible with the old config-host.mak variable names, the build will
>>> fail. Even if it does work, it's wasted effort since we'll need to
>>> rebuild them with the right config-host.mak settings immediately.
>>>
>>> Instead, make the generated headers depend on config-host.mak
>>> and config-target.mak. This means we'll definitely rebuild them
>>> if the configuration changes, but it will be done after Make
>>> reloads its makefiles and includes so will happen with the
>>> correct set of config-host.mak settings.
>>>
>>> We rely on the various .o files having correct autogenerated
>>> dependency rules to cause the generated headers to be generated
>>> as and when they are needed.
>
>> Reviewed-by: Paolo Bonzini <address@hidden>

> Any objections to this going into 2.1 for rc1 ?

Unfortunately it doesn't seem to work correctly for a build
from clean:

e104462:trusty:qemu-for-merges$ make -C build/alldbg V=1
make: Entering directory `/home/petmay01/linaro/qemu-for-merges/build/alldbg'
libtool  --mode=compile --tag=CC ccache gcc
-I/home/petmay01/linaro/qemu-for-merges/tcg
-I/home/petmay01/linaro/qemu-for-merges/tcg/i386
-I/home/petmay01/linaro/qemu-for-merges/linux-headers
-I/home/petmay01/linaro/qemu-for-merges/build/alldbg/linux-headers -I.
-I/home/petmay01/linaro/qemu-for-merges
-I/home/petmay01/linaro/qemu-for-merges/include
-I/home/petmay01/linaro/qemu-for-merges/libcacard -Ilibcacard -Werror
-fPIE -DPIE -m64 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64
-D_LARGEFILE_SOURCE -Wstrict-prototypes -Wredundant-decls -Wall
-Wundef -Wwrite-strings -Wmissing-prototypes -fno-strict-aliasing
-fno-common  -Wendif-labels -Wmissing-include-dirs -Wempty-body
-Wnested-externs -Wformat-security -Wformat-y2k -Winit-self
-Wignored-qualifiers -Wold-style-declaration -Wold-style-definition
-Wtype-limits -fstack-protector-all   -I/usr/include/p11-kit-1
-I/usr/include/p11-kit-1     -I/usr/include/libpng12
-I/usr/include/spice-server -I/usr/include/glib-2.0
-I/usr/lib/x86_64-linux-gnu/glib-2.0/include -I/usr/include/pixman-1
-I/usr/include/spice-1   -I/usr/include/libusb-1.0
-I/usr/include/pixman-1
-I/home/petmay01/linaro/qemu-for-merges/tests -MMD -MP -MT
libcacard/cac.lo -MF libcacard/cac.d -pthread -I/usr/include/glib-2.0
-I/usr/lib/x86_64-linux-gnu/glib-2.0/include   -g   -c -o
libcacard/cac.lo /home/petmay01/linaro/qemu-for-merges/libcacard/cac.c
libtool: compile:  ccache gcc
-I/home/petmay01/linaro/qemu-for-merges/tcg
-I/home/petmay01/linaro/qemu-for-merges/tcg/i386
-I/home/petmay01/linaro/qemu-for-merges/linux-headers
-I/home/petmay01/linaro/qemu-for-merges/build/alldbg/linux-headers -I.
-I/home/petmay01/linaro/qemu-for-merges
-I/home/petmay01/linaro/qemu-for-merges/include
-I/home/petmay01/linaro/qemu-for-merges/libcacard -Ilibcacard -Werror
-DPIE -m64 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE
-Wstrict-prototypes -Wredundant-decls -Wall -Wundef -Wwrite-strings
-Wmissing-prototypes -fno-strict-aliasing -fno-common -Wendif-labels
-Wmissing-include-dirs -Wempty-body -Wnested-externs -Wformat-security
-Wformat-y2k -Winit-self -Wignored-qualifiers -Wold-style-declaration
-Wold-style-definition -Wtype-limits -fstack-protector-all
-I/usr/include/p11-kit-1 -I/usr/include/p11-kit-1
-I/usr/include/libpng12 -I/usr/include/spice-server
-I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include
-I/usr/include/pixman-1 -I/usr/include/spice-1
-I/usr/include/libusb-1.0 -I/usr/include/pixman-1
-I/home/petmay01/linaro/qemu-for-merges/tests -MMD -MP -MT
libcacard/cac.lo -MF libcacard/cac.d -pthread -I/usr/include/glib-2.0
-I/usr/lib/x86_64-linux-gnu/glib-2.0/include -g -c
/home/petmay01/linaro/qemu-for-merges/libcacard/cac.c  -fPIC -DPIC -o
libcacard/.libs/cac.o
In file included from
/home/petmay01/linaro/qemu-for-merges/include/qemu-common.h:15:0,
                 from /home/petmay01/linaro/qemu-for-merges/libcacard/cac.c:8:
/home/petmay01/linaro/qemu-for-merges/include/qemu/compiler.h:6:25:
fatal error: config-host.h: No such file or directory
 #include "config-host.h"
                         ^
compilation terminated.

We're trying to do a "build .o file and .d file in the same go"
gcc command, so the fact that we don't have the generated header
yet causes us to blow up. This would work if we built the .d files
separately using -MG to tell gcc to ignore missing headers...

thanks
-- PMM