[PATCH] Makefile.am: don't confuse CFLAGS and CFLAGS_FOR_BUILD

Thomas De Schampheleire patrickdepinguin at gmail.com
Tue Dec 6 20:06:08 UTC 2016 

Hi Dmitry,

On Wed, Nov 16, 2016 at 8:27 PM, Dmitry V. Levin <ldv at altlinux.org> wrote:
> Hi,
>
> On Tue, Oct 18, 2016 at 01:42:44PM +0200, Thomas De Schampheleire wrote:
>> From: Thomas De Schampheleire <thomas.de_schampheleire at nokia.com>
>>
>> Commit dc427d50d96b15c9a64d7e78d97ce4d194622a63 enabled a number of extra
>> warning flags through configure.ac. The configure script will determine
>> dynamically if CC supports these flags before adding them to WARN_CFLAGS.
>>
>> ioctlsort is compiled with CC_FOR_BUILD, rather than CC. Nevertheless, the
>> flags passed to this compilation also include WARN_CFLAGS (through
>> AM_CFLAGS). This is incorrect: in a cross-compilation use case, CC and
>> CC_FOR_BUILD are not the same. The former is the cross-compiler,
>> the latter is the host compiler. Both may be of different versions and
>> support different warning flags.
>>
>> In particular, this posed a problem when cross-compiling with a host
>> compiler gcc 4.1, which does not support all the new flags:
>>
>>     /usr/bin/gcc -DHAVE_CONFIG_H   -I./linux/arm -I./linux/arm -I./linux
>>     -I./linux -I. -I. -I/host-sysroot/usr/include -Wall -Wempty-body
>>     -Wformat-security -Wignored-qualifiers -Winit-self -Wlogical-op
>>     -Wmissing-parameter-type -Wnested-externs -Wold-style-declaration
>>     -Wold-style-definition -Wsign-compare -Wtype-limits -Wwrite-strings -O2
>>     -I/host-sysroot/usr/include -DIOCTLSORT_INC=\"ioctls_all0.h\" -c -o
>>     ioctlsort0.o ./ioctlsort.c
>>     cc1: error: unrecognized command line option "-Wempty-body"
>>     cc1: error: unrecognized command line option "-Wignored-qualifiers"
>>     cc1: error: unrecognized command line option "-Wlogical-op"
>>     cc1: error: unrecognized command line option "-Wmissing-parameter-type"
>>     cc1: error: unrecognized command line option "-Wold-style-declaration"
>>     cc1: error: unrecognized command line option "-Wtype-limits"
>>     make[2]: *** [ioctlsort0.o] Error 1
>>
>> Fix by introducing AM_C/CPP/LDFLAGS_FOR_BUILD which are empty by default.
>> Only AM_CPPFLAGS_FOR_BUILD actually needs to be filled for now, based on
>> AM_CPPFLAGS.
>>
>> Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire at nokia.com>
>
> Good catch.  Unfortunately, the change you propose also strips all
> WARN_CFLAGS from the build of ioctlsort executable, which is certainly
> not what we want.
>
> The correct fix is going to be more complex, e.g.
> - move all gl_WARN_ADD/WARN_CFLAGS related code from configure.ac to a
>   separate m4 macro, say st_WARN_CFLAGS;
> - call st_WARN_CFLAGS in configure.ac;
> - modify AX_PROG_CC_FOR_BUILD to
>   + pushdef WARN_CFLAGS to WARN_CFLAGS_FOR_BUILD,
>   + call st_WARN_CFLAGS,
>   + popdef WARN_CFLAGS back,
>   + AC_SUBST WARN_CFLAGS_FOR_BUILD;
> - add WARN_CFLAGS_FOR_BUILD to AM_CFLAGS_FOR_BUILD.
>

Thanks for the suggestion.
I tried implementing it but got stuck. What I observe is that the
second invocation of ST_WARN_CFLAGS is using cached results, which
should not happen because the compiler can be different. Looking at
the definition of gl_WARN_ADD, I think that the cache_id of the
AC_CACHE_CHECK call in gl_COMPILER_OPTION_IF should contain CC or a
similar variable, so that caching does not happen.

I'm sending what I have for now below.

commit 535960a637b2b8db85170ede95e8471abf9bd2e2
Author: Thomas De Schampheleire <thomas.de_schampheleire at nokia.com>
Date:   Thu Oct 13 15:40:31 2016 +0200

    Makefile.am: don't confuse CFLAGS and CFLAGS_FOR_BUILD

    Commit dc427d50d96b15c9a64d7e78d97ce4d194622a63 enabled a number of extra
    warning flags through configure.ac. The configure script will determine
    dynamically if CC supports these flags before adding them to WARN_CFLAGS.

    ioctlsort is compiled with CC_FOR_BUILD, rather than CC. Nevertheless, the
    flags passed to this compilation also include WARN_CFLAGS (through
    AM_CFLAGS). This is incorrect: in a cross-compilation use case, CC and
    CC_FOR_BUILD are not the same. The former is the cross-compiler,
    the latter is the host compiler. Both may be of different versions and
    support different warning flags.

    In particular, this posed a problem when cross-compiling with a host
    compiler gcc 4.1, which does not support all the new flags:

        /usr/bin/gcc -DHAVE_CONFIG_H   -I./linux/arm -I./linux/arm -I./linux
        -I./linux -I. -I. -I/host-sysroot/usr/include -Wall -Wempty-body
        -Wformat-security -Wignored-qualifiers -Winit-self -Wlogical-op
        -Wmissing-parameter-type -Wnested-externs -Wold-style-declaration
        -Wold-style-definition -Wsign-compare -Wtype-limits -Wwrite-strings -O2
        -I/host-sysroot/usr/include -DIOCTLSORT_INC=\"ioctls_all0.h\" -c -o
        ioctlsort0.o ./ioctlsort.c
        cc1: error: unrecognized command line option "-Wempty-body"
        cc1: error: unrecognized command line option "-Wignored-qualifiers"
        cc1: error: unrecognized command line option "-Wlogical-op"
        cc1: error: unrecognized command line option "-Wmissing-parameter-type"
        cc1: error: unrecognized command line option "-Wold-style-declaration"
        cc1: error: unrecognized command line option "-Wtype-limits"
        make[2]: *** [ioctlsort0.o] Error 1

    Fix by introducing AM_C/CPP/LDFLAGS_FOR_BUILD which are empty by default.
    Only AM_CPPFLAGS_FOR_BUILD actually needs to be filled for now, based on
    AM_CPPFLAGS.

diff --git a/Makefile.am b/Makefile.am
index 69dd2be..460a1d5 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -52,6 +52,8 @@ AM_CPPFLAGS = -I$(builddir)/$(OS)/$(ARCH) \
           -I$(srcdir)/$(OS) \
           -I$(builddir) \
           -I$(srcdir)
+AM_CFLAGS_FOR_BUILD = $(WARN_CFLAGS_FOR_BUILD)
+AM_CPPFLAGS_FOR_BUILD = $(AM_CPPFLAGS)

 include xlat/Makemodule.am

@@ -793,9 +795,9 @@ news-check: NEWS
 ioctlsort_CC = $(CC_FOR_BUILD)
 ioctlsort_DEFS = $(DEFS)
 ioctlsort_INCLUDES = $(DEFAULT_INCLUDES) $(INCLUDES)
-ioctlsort_CPPFLAGS = $(AM_CPPFLAGS) $(CPPFLAGS_FOR_BUILD)
-ioctlsort_CFLAGS = $(AM_CFLAGS) $(CFLAGS_FOR_BUILD)
-ioctlsort_LDFLAGS = $(AM_LDFLAGS) $(LDFLAGS_FOR_BUILD)
+ioctlsort_CPPFLAGS = $(AM_CPPFLAGS_FOR_BUILD) $(CPPFLAGS_FOR_BUILD)
+ioctlsort_CFLAGS = $(AM_CFLAGS_FOR_BUILD) $(CFLAGS_FOR_BUILD)
+ioctlsort_LDFLAGS = $(AM_LDFLAGS_FOR_BUILD) $(LDFLAGS_FOR_BUILD)

 ioctls_inc_h = $(wildcard $(srcdir)/$(OS)/$(ARCH)/ioctls_inc*.h)
 ioctlent_h = $(patsubst
$(srcdir)/$(OS)/$(ARCH)/ioctls_inc%,ioctlent%,$(ioctls_inc_h))
diff --git a/configure.ac b/configure.ac
index 61dcf15..a5f50ee 100644
--- a/configure.ac
+++ b/configure.ac
@@ -251,27 +251,7 @@ esac
 AC_DEFINE_UNQUOTED([ENABLE_ARM_OABI], [$enable_arm_oabi],
            [Define to 1 if you want OABI support on ARM EABI.])

-gl_WARN_ADD([-Wall])
-gl_WARN_ADD([-Wempty-body])
-gl_WARN_ADD([-Wformat-security])
-gl_WARN_ADD([-Wignored-qualifiers])
-gl_WARN_ADD([-Winit-self])
-gl_WARN_ADD([-Wlogical-op])
-gl_WARN_ADD([-Wmissing-parameter-type])
-gl_WARN_ADD([-Wnested-externs])
-gl_WARN_ADD([-Wold-style-declaration])
-gl_WARN_ADD([-Wold-style-definition])
-gl_WARN_ADD([-Wsign-compare])
-gl_WARN_ADD([-Wtype-limits])
-gl_WARN_ADD([-Wwrite-strings])
-AC_ARG_ENABLE([gcc-Werror],
-  [AS_HELP_STRING([--enable-gcc-Werror], [turn on gcc's -Werror option])],
-  [case $enableval in
-     yes) gl_WARN_ADD([-Werror]) ;;
-     no)  ;;
-     *)   AC_MSG_ERROR([bad value $enableval for gcc-Werror option]) ;;
-   esac]
-)
+st_WARN_CFLAGS
 AC_SUBST([WARN_CFLAGS])

 AC_C_BIGENDIAN
diff --git a/m4/ax_prog_cc_for_build.m4 b/m4/ax_prog_cc_for_build.m4
index 77fd346..5520553 100644
--- a/m4/ax_prog_cc_for_build.m4
+++ b/m4/ax_prog_cc_for_build.m4
@@ -57,6 +57,7 @@ pushdef([CPP], CPP_FOR_BUILD)dnl
 pushdef([CFLAGS], CFLAGS_FOR_BUILD)dnl
 pushdef([CPPFLAGS], CPPFLAGS_FOR_BUILD)dnl
 pushdef([LDFLAGS], LDFLAGS_FOR_BUILD)dnl
+pushdef([WARN_CFLAGS], WARN_CFLAGS_FOR_BUILD)dnl
 pushdef([host], build)dnl
 pushdef([host_alias], build_alias)dnl
 pushdef([host_cpu], build_cpu)dnl
@@ -80,6 +81,8 @@ AC_PROG_CC
 AC_PROG_CPP
 AC_EXEEXT

+st_WARN_CFLAGS
+
 ac_tool_prefix=$save_ac_tool_prefix
 cross_compiling=$save_cross_compiling

@@ -98,6 +101,7 @@ popdef([host_vendor])dnl
 popdef([host_cpu])dnl
 popdef([host_alias])dnl
 popdef([host])dnl
+popdef([WARN_CFLAGS])dnl
 popdef([LDFLAGS])dnl
 popdef([CPPFLAGS])dnl
 popdef([CFLAGS])dnl
@@ -122,4 +126,5 @@ AC_SUBST(BUILD_OBJEXT)dnl
 AC_SUBST([CFLAGS_FOR_BUILD])dnl
 AC_SUBST([CPPFLAGS_FOR_BUILD])dnl
 AC_SUBST([LDFLAGS_FOR_BUILD])dnl
+AC_SUBST([WARN_CFLAGS_FOR_BUILD])dnl
 ])
diff --git a/m4/st_WARN_CFLAGS.m4 b/m4/st_WARN_CFLAGS.m4
new file mode 100644
index 0000000..6034714
--- /dev/null
+++ b/m4/st_WARN_CFLAGS.m4
@@ -0,0 +1,23 @@
+AC_DEFUN([st_WARN_CFLAGS], [dnl
+gl_WARN_ADD([-Wall])
+gl_WARN_ADD([-Wempty-body])
+gl_WARN_ADD([-Wformat-security])
+gl_WARN_ADD([-Wignored-qualifiers])
+gl_WARN_ADD([-Winit-self])
+gl_WARN_ADD([-Wlogical-op])
+gl_WARN_ADD([-Wmissing-parameter-type])
+gl_WARN_ADD([-Wnested-externs])
+gl_WARN_ADD([-Wold-style-declaration])
+gl_WARN_ADD([-Wold-style-definition])
+gl_WARN_ADD([-Wsign-compare])
+gl_WARN_ADD([-Wtype-limits])
+gl_WARN_ADD([-Wwrite-strings])
+AC_ARG_ENABLE([gcc-Werror],
+  [AS_HELP_STRING([--enable-gcc-Werror], [turn on gcc's -Werror option])],
+  [case $enableval in
+     yes) gl_WARN_ADD([-Werror]) ;;
+     no)  ;;
+     *)   AC_MSG_ERROR([bad value $enableval for gcc-Werror option]) ;;
+   esac]
+)
+])


Any help is appreciated (or feel free to take over based on the above
if you prefer).

Thanks,
Thomas

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