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

[Wen Congyang <wency@xxxxxxxxxxxxxx>]

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]
 #  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)
-- 
2.1.0


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