Re: [Xen-devel] [PATCH v2] tools/Rules.mk: Don't optimize debug builds; add macro debugging information

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2015-01-13 at 13:52 +0800, Wen Congyang wrote:
> On 12/01/2014 10:21 PM, Euan Harris wrote:
> > Tools debug builds are built with optimization level -O1, inherited from
> > the CFLAGS definition in StdGNU.mk.   Optimizations confuse the debugger,
> > and the comment justifying -O1 in StdGNU.mk should not apply for a
> > userspace library.   Disable optimization by appending -O0 to CFLAGS,
> > which overrides the -O1 flag specified earlier.
> > 
> > Also specify -g3, to add macro debugging information which allows
> > gdb to expand macro invocations.   This is useful as libxl uses many
> > non-trivial macros.
> > 
> > Signed-off-by: Euan Harris <euan.harris@xxxxxxxxxx>
> > 
> > Changes since v1:
> >   * moved flag override to tools/Rules.mk so it affects all tools
> > ---
> >  tools/Rules.mk |    5 +++++
> >  1 files changed, 5 insertions(+), 0 deletions(-)
> > 
> > diff --git a/tools/Rules.mk b/tools/Rules.mk
> > index 87a56dc..7ef1ce5 100644
> > --- a/tools/Rules.mk
> > +++ b/tools/Rules.mk
> > @@ -54,6 +54,11 @@ CFLAGS_libxenvchan = -I$(XEN_LIBVCHAN)
> >  LDLIBS_libxenvchan = $(SHLIB_libxenctrl) $(SHLIB_libxenstore) 
> > -L$(XEN_LIBVCHAN) -lxenvchan
> >  SHLIB_libxenvchan  = -Wl,-rpath-link=$(XEN_LIBVCHAN)
> >  
> > +ifeq ($(debug),y)
> > +# Disable optimizations and debugging information for macros
> > +CFLAGS += -O0 -g3
> > +endif
> > +
> >  LIBXL_BLKTAP ?= $(CONFIG_BLKTAP2)
> >  
> >  ifeq ($(LIBXL_BLKTAP),y)
> > 
> 
> This patch causes a building error:
> gcc -fno-strict-aliasing -O2 -g -pipe -Wall -Werror=format-security 
> -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong 
> --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic 
> -D_GNU_SOURCE -fPIC -fwrapv -DNDEBUG -O2 -g -pipe -Wall 
> -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions 
> -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 
> -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv -O1 -fno-omit-frame-pointer -m64 
> -g -fno-strict-aliasing -std=gnu99 -Wall -Wstrict-prototypes 
> -Wdeclaration-after-statement -Wno-unused-but-set-variable 
> -Wno-unused-local-typedefs -O0 -g3 -D__XEN_TOOLS__ -MMD -MF .install.d 
> -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -fno-optimize-sibling-calls -fPIC 
> -I../../tools/include -I../../tools/libxc/include -Ixen/lowlevel/xc 
> -I/usr/include/python2.7 -c xen/lowlevel/xc/xc.c -o 
> build/temp.linux-x86_64-2.7/xen/lowlevel/xc/xc.o -fno-strict-aliasing -Werror
> In file included from /usr/include/limits.h:25:0,
>                  from 
> /usr/lib/gcc/x86_64-redhat-linux/4.9.2/include/limits.h:168,
>                  from 
> /usr/lib/gcc/x86_64-redhat-linux/4.9.2/include/syslimits.h:7,
>                  from 
> /usr/lib/gcc/x86_64-redhat-linux/4.9.2/include/limits.h:34,
>                  from /usr/include/python2.7/Python.h:19,
>                  from xen/lowlevel/xc/xc.c:7:
> /usr/include/features.h:328:4: error: #warning _FORTIFY_SOURCE requires 
> compiling with optimization (-O) [-Werror=cpp]

Where is _FORTIFY_SOURCE coming from? I don't see it in our tree
anywhere except stubdom/Makefile which is disabling it and the build
worked for me. Perhaps it is coming from your build environment
somewhere? How are you configuring and building Xen?

Maybe what we want to do is only disable optimisations if debug=y AND
-D_FORTIFY_SOURCE is not set? Might involve some autoconf checks to
determine the fortification level in the user provided CFLAGS, which
might be a bit faffsome.

Ian.

>  #  warning _FORTIFY_SOURCE requires compiling with optimization (-O)
>     ^
> cc1: all warnings being treated as errors
> error: command 'gcc' failed with exit status 1
> 
> The following patch can fix this problem:
> 
> From d16961971e14f6e50f9a9905449929d5a7c60860 Mon Sep 17 00:00:00 2001
> From: Wen Congyang <wency@xxxxxxxxxxxxxx>
> Date: Tue, 13 Jan 2015 12:05:30 +0800
> Subject: [PATCH] Fix a building error
> 
> Commit 1166ecf7 disables optimization. But _FORTIFY_SOURCE
> requires compiling with optimization (-O). Disable _FORTIFY_SOURCE
> by appending -Wp,-U_FORTIFY_SOURCE to CFLAGS.
> 
> Signed-off-by: Wen Congyang <wency@xxxxxxxxxxxxxx>
> ---
>  tools/Rules.mk | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/Rules.mk b/tools/Rules.mk
> index 962a743..8ad1b05 100644
> --- a/tools/Rules.mk
> +++ b/tools/Rules.mk
> @@ -56,7 +56,7 @@ SHLIB_libxenvchan  = -Wl,-rpath-link=$(XEN_LIBVCHAN)
>  
>  ifeq ($(debug),y)
>  # Disable optimizations and enable debugging information for macros
> -CFLAGS += -O0 -g3
> +CFLAGS += -O0 -g3 -Wp,-U_FORTIFY_SOURCE
>  endif
>  
>  LIBXL_BLKTAP ?= $(CONFIG_BLKTAP2)



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