gcc - toshi_hirasawaの日記

主要なパートのバージョンの確認方法は

binutils ld -v
http://d.hatena.ne.jp/toshi_hirasawa/20120202/1328189742
GCC gcc --version
glibc GNU C ライブラリ(libc6) /sbin/ldconfig -V
標準ライブラリ・ヘッダーファイル(libc6-dev) file /usr/include/stdio.h
Linux 専用ライブラリ・ヘッダーファイル cat /usr/include/linux/version.h

cpp .. pre processor
cc1 .. c compiler
cc1plus .. c++ compiler
collect2 .. ld front end
libgcc.a .. gcc library
crt*.o .. start-up routine(s) C RunTime startup routines
crt1 crti crtbegin and crtend crtnの順番

[hirasawa@ubunt1004-32-2 gcc-Programming-Kobo]$ gcc -v -save-temps -o hello hello.c
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.3-4ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-plugin --enable-objc-gc --enable-targets=all --disable-werror --with-arch-32=i486 --with-tune=generic --enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu --target=i486-linux-gnu
Thread model: posix
gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5) 
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-o' 'hello' '-mtune=generic' '-march=i486'
 /usr/lib/gcc/i486-linux-gnu/4.4.3/cc1 -E -quiet -v hello.c -D_FORTIFY_SOURCE=2 -mtune=generic -march=i486 -fpch-preprocess -fstack-protector -o hello.i
ignoring nonexistent directory "/usr/local/include/i486-linux-gnu"
ignoring nonexistent directory "/usr/lib/gcc/i486-linux-gnu/4.4.3/../../../../i486-linux-gnu/include"
ignoring nonexistent directory "/usr/include/i486-linux-gnu"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/lib/gcc/i486-linux-gnu/4.4.3/include
 /usr/lib/gcc/i486-linux-gnu/4.4.3/include-fixed
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-o' 'hello' '-mtune=generic' '-march=i486'
 /usr/lib/gcc/i486-linux-gnu/4.4.3/cc1 -fpreprocessed hello.i -quiet -dumpbase hello.c -mtune=generic -march=i486 -auxbase hello -version -fstack-protector -o hello.s
GNU C (Ubuntu 4.4.3-4ubuntu5) version 4.4.3 (i486-linux-gnu)
	compiled by GNU C version 4.4.3, GMP version 4.3.2, MPFR version 2.4.2-p1.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C (Ubuntu 4.4.3-4ubuntu5) version 4.4.3 (i486-linux-gnu)
	compiled by GNU C version 4.4.3, GMP version 4.3.2, MPFR version 2.4.2-p1.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 5998ce5f1765e99eea5269f4c1e38d44
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-o' 'hello' '-mtune=generic' '-march=i486'
 as -V -Qy -o hello.o hello.s
GNU assembler version 2.20.1 (i486-linux-gnu) using BFD version (GNU Binutils for Ubuntu) 2.20.1-system.20100303
COMPILER_PATH=/usr/lib/gcc/i486-linux-gnu/4.4.3/:/usr/lib/gcc/i486-linux-gnu/4.4.3/:/usr/lib/gcc/i486-linux-gnu/:/usr/lib/gcc/i486-linux-gnu/4.4.3/:/usr/lib/gcc/i486-linux-gnu/:/usr/lib/gcc/i486-linux-gnu/4.4.3/:/usr/lib/gcc/i486-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/i486-linux-gnu/4.4.3/:/usr/lib/gcc/i486-linux-gnu/4.4.3/:/usr/lib/gcc/i486-linux-gnu/4.4.3/../../../../lib/:/lib/../lib/:/usr/lib/../lib/:/usr/lib/gcc/i486-linux-gnu/4.4.3/../../../:/lib/:/usr/lib/:/usr/lib/i486-linux-gnu/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-o' 'hello' '-mtune=generic' '-march=i486'
 /usr/lib/gcc/i486-linux-gnu/4.4.3/collect2 --build-id --eh-frame-hdr -m elf_i386 --hash-style=both -dynamic-linker /lib/ld-linux.so.2 -o hello -z relro /usr/lib/gcc/i486-linux-gnu/4.4.3/../../../../lib/crt1.o /usr/lib/gcc/i486-linux-gnu/4.4.3/../../../../lib/crti.o /usr/lib/gcc/i486-linux-gnu/4.4.3/crtbegin.o -L/usr/lib/gcc/i486-linux-gnu/4.4.3 -L/usr/lib/gcc/i486-linux-gnu/4.4.3 -L/usr/lib/gcc/i486-linux-gnu/4.4.3/../../../../lib -L/lib/../lib -L/usr/lib/../lib -L/usr/lib/gcc/i486-linux-gnu/4.4.3/../../.. -L/usr/lib/i486-linux-gnu hello.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/i486-linux-gnu/4.4.3/crtend.o /usr/lib/gcc/i486-linux-gnu/4.4.3/../../../../lib/crtn.o
[hirasawa@ubunt1004-32-2 gcc-Programming-Kobo]$

hello.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed

ふむ、ldのオプションの no-as-neededとかってなんだろ?

gcc -v -nostartfiles hello.c .. crt*oファイル群のリンクを中止する。
　　(hello.oまでは通常通りで、ldの時の動作の変更のお話です）

 /usr/lib/gcc/i486-linux-gnu/4.4.3/collect2 --build-id --eh-frame-hdr -m elf_i386 --hash-style=both -dynamic-linker /lib/ld-linux.so.2 -o hello -z relro -L/usr/lib/gcc/i486-linux-gnu/4.4.3 -L/usr/lib/gcc/i486-linux-gnu/4.4.3 -L/usr/lib/gcc/i486-linux-gnu/4.4.3/../../../../lib -L/lib/../lib -L/usr/lib/../lib -L/usr/lib/gcc/i486-linux-gnu/4.4.3/../../.. -L/usr/lib/i486-linux-gnu /tmp/ccbz6sEI.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed
/usr/bin/ld: warning: cannot find entry symbol _start; defaulting to 0000000008048220

プログラムの開始アドレス(entry point)を_startからmainに変えるために -eオプションをつかってみると

[hirasawa@ubunt1004-32-2 gcc-Programming-Kobo]$ ld -e main -o hello hello.ohello.o: In function `main':
hello.c:(.text+0x11): undefined reference to `puts'
[hirasawa@ubunt1004-32-2 gcc-Programming-Kobo]$

筋道通り、つぎはシステムコールのwriteの調査
man 2 writeを叩いて、hello2.cを書いてみませう

       #include <unistd.h>

       ssize_t write(int fd, const void *buf, size_t count);


[hirasawa@ubunt1004-32-2 gcc-Programming-Kobo]$ cat ./hello2.c 
#include <unistd.h>
#define MSG "hello\n"

int main(void)
{
ssize_t ret;
ret = write(1 , MSG , sizeof(MSG));
return ret;
}
[hirasawa@ubunt1004-32-2 gcc-Programming-Kobo]$ 
[hirasawa@ubunt1004-32-2 gcc-Programming-Kobo]$ gcc -Wall -save-temps -o hello2 hello2.c 
[hirasawa@ubunt1004-32-2 gcc-Programming-Kobo]$ ./hello2 
hello

[hirasawa@ubunt1004-32-2 gcc-Programming-Kobo]$ ld -e main -o hello2 hello2.o
hello2.o: In function `main':
hello2.c:(.text+0x21): undefined reference to `write'
[hirasawa@ubunt1004-32-2 gcc-Programming-Kobo]$

systemCall writeもまた、ライブラリ関数の一部ってことを再確認。

つづきは、拡張アッセンブラにつづく。