在Makefile.in中这样定义规则：

bconfig.h: cs-bconfig.h ; @true

cs-bconfig.h: Makefile

     TARGET_CPU_DEFAULT="" \

     HEADERS="$(build_xm_include_list)" DEFINES="$(build_xm_defines)" \

     $(SHELL) $(srcdir)/mkconfig.sh bconfig.h

即bconfig.h的生成是通过mkconfig.sh bconfig.h这个命令来实现的。

下面对照mkconfig.sh的内容生成bconfig.h文件。

1.1.1.1             调用参数判断

# Generate gcc's various configuration headers:

# config.h, tconfig.h, bconfig.h, tm.h, and tm_p.h.

# $1 is the file to generate.  DEFINES, HEADERS, and possibly

# TARGET_CPU_DEFAULT are expected to be set in the environment.

if [ -z "$1" ]; then

    echo "Usage: DEFINES='list' HEADERS='list' \\" >&2

    echo "  [TARGET_CPU_DEFAULT='default'] mkconfig.sh FILE" >&2

    exit 1

fi

判断是否带参数执行，从Makefile调用命令来看$1 = “bconfig.h”。

1.1.1.2             删除临时文件

output=$1

rm -f ${output}T

删除输出的临时文件。

1.1.1.3             输出保护性语句

# This converts a file name into header guard macro format.

hg_sed_expr='y,abcdefghijklmnopqrstuvwxyz./,ABCDEFGHIJKLMNOPQRSTUVWXYZ__,'

header_guard=GCC_`echo ${output} | sed -e ${hg_sed_expr}`

# Add multiple inclusion protection guard, part one.

echo "#ifndef ${header_guard}" >> ${output}T

echo "#define ${header_guard}" >> ${output}T

这几句话其实就是在头文件中输出

#ifndef xxx

#define xxx

这样的保护性语句。

1.1.1.4             错误判断

# A special test to ensure that build-time files don't blindly use

# config.h.

if test x"$output" = x"config.h"; then

  echo "#ifdef GENERATOR_FILE" >> ${output}T

  echo "#error config.h is for the host, not build, machine." >> ${output}T

  echo "#endif" >> ${output}T

fi

我们需要生成bconfig.h，这段话可略过。

1.1.1.5             定义TARGET_CPU_DEFAULT

# Define TARGET_CPU_DEFAULT if the system wants one.

# This substitutes for lots of *.h files.

if [ "$TARGET_CPU_DEFAULT" != "" ]; then

    echo "#define TARGET_CPU_DEFAULT ($TARGET_CPU_DEFAULT)" >> ${output}T

fi

对于bconfig.h来讲，TARGET_CPU_DEFAULT为空字符串，这段将不执行。

1.1.1.6             输出宏定义

# Provide defines for other macros set in config.gcc for this file.

for def in $DEFINES; do

    echo "#ifndef $def" | sed 's/=.*//' >> ${output}T

    echo "# define $def" | sed 's/=/ /' >> ${output}T

    echo "#endif" >> ${output}T

done

这段话的输出取决于调用时的DEFINES定义，而这一变量在Makefile中定义为build_xm_defines，在Makefile.in中查找这个变量的定义：

build_xm_defines=@build_xm_defines@

说明这个值的定义应该是从configure中来的，在configure中查找可以发现这个值的定义为空，所以mkconfig.sh中的这段话将不产生输出。

1.1.1.7             输出include

# The first entry in HEADERS may be auto-FOO.h ;

# it wants to be included even when not -DIN_GCC.

if [ -n "$HEADERS" ]; then

    set $HEADERS

    case "$1" in auto-* )

     echo "#include \"$1\"" >> ${output}T

     shift

     ;;

    esac

    if [ $# -ge 1 ]; then

     echo '#ifdef IN_GCC' >> ${output}T

     for file in "$@"; do

         echo "# include \"$file\"" >> ${output}T

     done

     echo '#endif' >> ${output}T

    fi

fi

这段话将根据HEADERS的定义生成一些include语句。查找build_xm_include_list，可以发现以下定义：

build_xm_file_list=

for f in $build_xm_file; do

  case $f in

    ansidecl.h )

       build_xm_file_list="${build_xm_file_list} \$(srcdir)/../include/$f"

       build_xm_include_list="${build_xm_include_list} $f"

       ;;

    auto-build.h | auto-host.h )

       build_xm_file_list="${build_xm_file_list} $f"

       build_xm_include_list="${build_xm_include_list} $f"

       ;;

    * )

       build_xm_file_list="${build_xm_file_list} \$(srcdir)/config/$f"

       build_xm_include_list="${build_xm_include_list} config/$f"

       ;;

  esac

done

再查一下build_xm_file的定义，在config.build中：

  i[34567]86-*-cygwin* | i[34567]86-*-pe )

    build_xm_file=i386/xm-cygwin.h

    build_exeext=.exe

    ;;

因为我们选择vs2005做为host的编译器，因此在系统中并不直接支持，为此仿照configs/i386/xm-cygwin.h建立一个xm-vs2005.h文件，其内容与xm-cygwin.h相同。

在configure脚本中还有这样的语句：

build_xm_file="${build_auto} ansidecl.h ${build_xm_file}"

这里build_auto的定义为：

# auto-host.h is the file containing items generated by autoconf and is

# the first file included by config.h.

# If host=build, it is correct to have bconfig include auto-host.h

# as well.  If host!=build, we are in error and need to do more

# work to find out the build config parameters.

if test x$host = x$build

then

     build_auto=auto-host.h

else

…………..

fi

所以最后build_xm_include_list就变成了

“auto-host.h ansidecl.h config/i386/xm-vs2005.h”

回到mkconfig.sh的代码中来，上述代码段将生成如下输出：

#include "auto-host.h"

#ifdef IN_GCC

# include "../include/ansidecl.h"

# include "config/i386/xm-vs2005.h"

#endif

1.1.1.8             对tm.h做特殊处理

# If this is tm.h, now include insn-constants.h and insn-flags.h only

# if IN_GCC is defined but neither GENERATOR_FILE nor USED_FOR_TARGET

# is defined.  (Much of this is temporary.)

case $output in

    tm.h )

        cat >> ${output}T <<EOF

#if defined IN_GCC && !defined GENERATOR_FILE && !defined USED_FOR_TARGET

# include "insn-constants.h"

# include "insn-flags.h"

#endif

EOF

    ;;

esac

这几行代码将对tm.h输出一些特定的语句，但我们生成的是bconfig.h，故略过。

1.1.1.9             #endif

# Add multiple inclusion protection guard, part two.

echo "#endif /* ${header_guard} */" >> ${output}T

输出头文件末尾的#endif，与文件开头中的#ifndef对应。

1.1.1.10       文件后继处理

# Avoid changing the actual file if possible.

if [ -f $output ] && cmp ${output}T $output >/dev/null 2>&1; then

    echo $output is unchanged >&2

    rm -f ${output}T

else

    mv -f ${output}T $output

fi

# Touch a stamp file for Make's benefit.

rm -f cs-$output

echo timestamp > cs-$output

没什么，最后就是把临时文件复制为正式的bconfig.h。

1.1.1.11       最终版本

最后生成的bconfig.h如下：

#ifndef __GCC_BCONFIG_H__

#define __GCC_BCONFIG_H__

#include "auto-host.h"

#ifdef IN_GCC

# include "../include/ansidecl.h"

# include "config/i386/xm-vs2005.h"

#endif

#endif //__GCC_BCONFIG_H__