关于gcc, binutils, glibc

swordhui · 发表于 2010-4-18 16:02:10

先写个简单的程序

#include <stdio.h>
int main()
{
printf("Hello,world\n");
return 0;
}

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然后分别在4种情况下编译:

1. 使用主系统的gcc, binutils,和glibc

先编译: gcc -v -c test.c
输出如下

红色是我加的注释)

Using built-in specs.
[color="Red"]#疑问1: 什么是内建的specs? 什么时候不用内建的specs?

Target: i686-pc-linux-gnu

Configured with: ../gcc-4.4.0/configure --prefix=/usr --libexecdir=/usr/lib --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --enable-languages=c,c++ --disable-bootstrap

Thread model: posix
[color="Red"]疑问2: 还有什么thread model?

gcc version 4.4.0 (GCC)
COLLECT_GCC_OPTIONS='-v' '-c' '-mtune=generic'
/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/cc1 -quiet -v test.c -quiet -dumpbase test.c -mtune=generic -auxbase test -version -o /tmp/ccMeTqhk.s
[color="Blue"]#第一步用cc1, 将C语言变为汇编文件,在/tmp下

[color="Red"]疑问3: -mtune是什么? 都有什么-mtune?

ignoring nonexistent directory "/usr/local/include"
ignoring nonexistent directory "/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/../../../../i686-pc-linux-gnu/include"
[color="Blue"]这是干什么?!

#include "..." search starts here:

#include <...> search starts here:
/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/include
/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/include-fixed
[color="Red"]疑问4: 这些目录下都有啥? 什么程序用这些目录下的头文件?

/usr/include
End of search list.

GNU C (GCC) version 4.4.0 (i686-pc-linux-gnu)
compiled by GNU C version 4.4.0, GMP version 4.3.1, MPFR version 2.4.1.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 38b1ddb0d964ccbe49d98b715e55457e

COLLECT_GCC_OPTIONS='-v' '-c' '-mtune=generic'
as -V -Qy -o test.o /tmp/ccMeTqhk.s
[color="Red"]#第二步, 用binutils的as将汇编语言转换成object

GNU assembler version 2.19.1 (i686-pc-linux-gnu) using BFD version (GNU Binutils) 2.19.1

COMPILER_PATH=/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/:/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/:/usr/lib/gcc/i686-pc-linux-gnu/:/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/:/usr/lib/gcc/i686-pc-linux-gnu/:/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/:/usr/lib/gcc/i686-pc-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/:/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/:/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-c' '-mtune=generic'
OPSvr root #

OK, 我们先看看第一步输出的汇编语言

OPSvr tmp #cat ccMeTqhk.s
.file "test.c"
.section .rodata
.LC0:
.string "Hello,world"
.text
.globl main
.type main, @function
main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $16, %esp
movl $.LC0, (%esp)
call puts
movl $0, %eax
leave
ret
.size main, .-main
.ident "GCC: (GNU) 4.4.0"
.section .note.GNU-stack,"",@progbits

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Kao.. 由于printf没有参数,直接换成简单点的puts了. 这里面除了puts的函数名,没其他任何关于glibc的信息. 主要有两个段: .rodate和.text, 还有一个不知道要干嘛的.note.GNU-stack段.

再看看第二步的输出:

OPSvr root #readelf -a test.o
ELF Header:
Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
Class: ELF32
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: REL (Relocatable file)
Machine: Intel 80386
Version: 0x1
Entry point address: 0x0
Start of program headers: 0 (bytes into file)
Start of section headers: 192 (bytes into file)
Flags: 0x0
Size of this header: 52 (bytes)
Size of program headers: 0 (bytes)
Number of program headers: 0
Size of section headers: 40 (bytes)
Number of section headers: 11
Section header string table index: 8
Section Headers:
[Nr] Name Type Addr Off Size ES *** Lk Inf Al
[ 0] NULL 00000000 000000 000000 00 0 0 0
[ 1] .text PROGBITS 00000000 000034 00001c 00 AX 0 0 4
[ 2] .rel.text REL 00000000 00032c 000010 08 9 1 4
[ 3] .data PROGBITS 00000000 000050 000000 00 WA 0 0 4
[ 4] .bss NOBITS 00000000 000050 000000 00 WA 0 0 4
[ 5] .rodata PROGBITS 00000000 000050 00000c 00 A 0 0 1
[ 6] .comment PROGBITS 00000000 00005c 000012 00 0 0 1
[ 7] .note.GNU-stack PROGBITS 00000000 00006e 000000 00 0 0 1
[ 8] .shstrtab STRTAB 00000000 00006e 000051 00 0 0 1
[ 9] .symtab SYMTAB 00000000 000278 0000a0 10 10 8 4
[10] .strtab STRTAB 00000000 000318 000012 00 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings)
I (info), L (link order), G (group), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific)
There are no section groups in this file.
There are no program headers in this file.
Relocation section '.rel.text' at offset 0x32c contains 2 entries:
Offset Info Type Sym.Value Sym. Name
0000000c 00000501 R_386_32 00000000 .rodata
00000011 00000902 R_386_PC32 00000000 puts
There are no unwind sections in this file.
Symbol table '.symtab' contains 10 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 00000000 0 FILE LOCAL DEFAULT ABS test.c
2: 00000000 0 SECTION LOCAL DEFAULT 1
3: 00000000 0 SECTION LOCAL DEFAULT 3
4: 00000000 0 SECTION LOCAL DEFAULT 4
5: 00000000 0 SECTION LOCAL DEFAULT 5
6: 00000000 0 SECTION LOCAL DEFAULT 7
7: 00000000 0 SECTION LOCAL DEFAULT 6
8: 00000000 28 FUNC GLOBAL DEFAULT 1 main
9: 00000000 0 NOTYPE GLOBAL DEFAULT UND puts
No version information found in this file.

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可以看到蹦出了一堆段.
.text 从0x34开始,长0x1c
.rodata从0x50开始, 长0x0c

.rel.text指明了需要重定位的信息, 包括.rodata需要重新定位, puts需要重新定位. 谁来定位呢? puts需要在程序启动后动态定位

.data, .bss 程序中没有,程度都为0
.comment 干嘛用的? 18字节长 GCC: (GNU) 4.4.0
.shstrtab 从0x6e开始, 长0x51
.symtab从0x278开始,长0xa0
.strtab从138开始,长0x12
[color="Red"]疑问5, .shstrtab, .symtab, .strtab 干嘛用的?

反汇编一下, 看看和源码的区别:

OPSvr root #objdump -S test.o
test.o: file format elf32-i386
Disassembly of section .text:
00000000 <main>:
0: 55 push %ebp
1: 89 e5 mov %esp,%ebp
3: 83 e4 f0 and $0xfffffff0,%esp
6: 83 ec 10 sub $0x10,%esp
9: c7 04 24 00 00 00 00 movl $0x0,(%esp)
10: e8 fc ff ff ff call 11 <main+0x11>
15: b8 00 00 00 00 mov $0x0,%eax
1a: c9 leave
1b: c3 ret

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可以看出 $.LC0 直接变为0x0,
puts变为 <main+0x11> , 期待链接程序重新赋值

先不管它,我们接着进行第二步, 链接glibc.

OPSvr root #gcc -v -o test test.o
Using built-in specs.

Target: i686-pc-linux-gnu

Configured with: ../gcc-4.4.0/configure --prefix=/usr --libexecdir=/usr/lib --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --enable-languages=c,c++ --disable-bootstrap

Thread model: posix

gcc version 4.4.0 (GCC)
COMPILER_PATH=/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/:/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/:/usr/lib/gcc/i686-pc-linux-gnu/:/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/:/usr/lib/gcc/i686-pc-linux-gnu/:/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/:/usr/lib/gcc/i686-pc-linux-gnu/
[color="Red"]#这是在干嘛? 这么多重复的路径?!

LIBRARY_PATH=/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/:/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/:/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/../../../:/lib/:/usr/lib/
[color="Red"]#这个/usr/lib也重复了.. 电脑不糊涂,人脑糊涂了..

COLLECT_GCC_OPTIONS='-v' '-o' 'test' '-mtune=generic'
/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/collect2

[color="Red"]疑问6: 为什么用collect2, 不用ld?

--eh-frame-hdr
-m elf_i386
-dynamic-linker
/lib/ld-linux.so.2
-o test
/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/../../../crt1.o
#其实就是/usr/lib/crt1.o
[color="Red"]#疑问7 crt1.o是干嘛用的? gcc提供的还是glibc提供的?

/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/../../../crti.o
其实就是/usr/lib/crti.o
[color="Red"]疑问8 crti.o是干嘛用的? gcc提供的还是glibc提供的?

/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/crtbegin.o
疑问九 crtbegin.o是干嘛用的? gcc提供的还是glibc提供的?

-L/usr/lib/gcc/i686-pc-linux-gnu/4.4.0
-L/usr/lib/gcc/i686-pc-linux-gnu/4.4.0
-L/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/../../.. test.o
-lgcc
[color="Red"]疑问10, gcc库是干嘛用的?

--as-needed -lgcc_s
[color="Red"]疑问11, gcc_s库是干嘛用的?

--no-as-needed -lc
[color="Red"]疑问12, c库是glibc提供的?

-lgcc
[color="Red"]怎么又来一遍?!

--as-needed -lgcc_s
--no-as-needed /usr/lib/gcc/i686-pc-linux-gnu/4.4.0/crtend.o
[color="Red"]疑问13, crtend.o是干嘛用的?

/usr/lib/gcc/i686-pc-linux-gnu/4.4.0/../../../crtn.o
[color="Red"]疑问14, crtn.o是干嘛用的?

Kao..晕了链接一个简单的程序,需要这么这么多来自gcc和glibc的库...

swordhui · 发表于 2010-4-18 16:46:26

疑问1: 关于specs

可以通过 info gcc的3.15章了解.

swordhui · 发表于 2010-4-18 17:04:09

题外话, 如果没有LFS手册给大家看,怎么构建类似于LFS的系统? 应该苦练内功,先搞清楚内核, 然后搞清楚C库, 搞清楚gcc, 对开源世界的软件包分布有清楚的了解... 就差不多了.
内核, gcc, C库, 自由软件实乃四大武功秘籍
每个都够人喝一壶了..

swordhui · 发表于 2010-4-18 17:47:32

疑问2, 除了posix还有很多

-enable-threads=lib
Specify that lib is the thread support library. This affects the Objective-C compiler and runtime library, and exception handling for other languages like C++ and Java. The possibilities for lib are:

aix
      AIX thread support.
dce
      DCE thread support.
gnat
      Ada tasking support. For non-Ada programs, this setting is equivalent to `single'. When used in conjunction with the Ada run time, it causes GCC to use the same thread primitives as Ada uses. This option is necessary when using both Ada and the back end exception handling, which is the default for most Ada targets.
mach
      Generic MACH thread support, known to work on NeXTSTEP. (Please note that the file needed to support this configuration, gthr-mach.h, is missing and thus this setting will cause a known bootstrap failure.)
no
      This is an alias for `single'.
posix
      Generic POSIX/Unix98 thread support.
posix95
      Generic POSIX/Unix95 thread support.
rtems
      RTEMS thread support.
single
      Disable thread support, should work for all platforms.
solaris
      Sun Solaris 2/Unix International thread support. Only use this if you really need to use this legacy API instead of the default, `posix'.
vxworks
      VxWorks thread support.
win32
      Microsoft Win32 API thread support.
nks
      Novell Kernel Services thread support.

swordhui · 发表于 2010-4-18 17:54:24

疑问3, 在info gcc的 3.17.15
用-march就可以, 支持 generic, native[这样是编译时自动选择当前CPU类型], i386, i486, i586,pentium,i686,pentium2,pentium3,pentium3m,pentium-m,pentium4,pentium4m,prescott,nocora,core2,k6,k6-2,k6-3 .........

swordhui · 发表于 2010-4-18 18:27:40

疑问6, 可以从info gcc 的第20章找到.

swordhui · 发表于 2010-4-18 18:42:08

疑问7, crt1.o 由C库提供,我这里是glibc.
很简单的一段程序, 功能可以从glibc源码的注释中找到.

root:/usr/lib# objdump -S crt1.o
crt1.o: file format elf32-i386
Disassembly of section .text:
00000000 <_start>:
0: 31 ed xor %ebp,%ebp
2: 5e pop %esi
3: 89 e1 mov %esp,%ecx
5: 83 e4 f0 and $0xfffffff0,%esp
8: 50 push %eax
9: 54 push %esp
a: 52 push %edx
b: 68 00 00 00 00 push $0x0
10: 68 00 00 00 00 push $0x0
15: 51 push %ecx
16: 56 push %esi
17: 68 00 00 00 00 push $0x0
1c: e8 fc ff ff ff call 1d <_start+0x1d>
21: f4 hlt
22: 90 nop
23: 90 nop
root:/usr/lib#

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swordhui · 发表于 2010-4-18 18:59:41

疑问8, glibc提供的crti.o,代码如下:

root:~# objdump -S /usr/lib/crti.o
/usr/lib/crti.o: file format elf32-i386
Disassembly of section .init:
00000000 <_init>:
0: 55 push %ebp
1: 89 e5 mov %esp,%ebp
3: 53 push %ebx
4: 83 ec 04 sub $0x4,%esp
7: e8 00 00 00 00 call c <_init+0xc>
c: 5b pop %ebx
d: 81 c3 03 00 00 00 add $0x3,%ebx
13: 8b 93 00 00 00 00 mov 0x0(%ebx),%edx
19: 85 d2 test %edx,%edx
1b: 74 05 je 22 <_init+0x22>
1d: e8 fc ff ff ff call 1e <_init+0x1e>
Disassembly of section .fini:
00000000 <_fini>:
0: 55 push %ebp
1: 89 e5 mov %esp,%ebp
3: 53 push %ebx
4: 83 ec 04 sub $0x4,%esp
7: e8 00 00 00 00 call c <_fini+0xc>
c: 5b pop %ebx
d: 81 c3 03 00 00 00 add $0x3,%ebx
root:~#

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swordhui · 发表于 2010-4-18 19:04:22

疑问9, crtbgein.o由 gcc提供,不是由C库.
代码如下:

root:/tmp# objdump -S usr/lib/gcc/i686-pc-linux-gnu/4.4.3/crtbegin.o
usr/lib/gcc/i686-pc-linux-gnu/4.4.3/crtbegin.o: file format elf32-i386
Disassembly of section .text:
00000000 <__do_global_dtors_aux>:
0: 55 push %ebp
1: 89 e5 mov %esp,%ebp
3: 53 push %ebx
4: 83 ec 04 sub $0x4,%esp
7: 80 3d 00 00 00 00 00 cmpb $0x0,0x0
e: 75 3f jne 4f <__do_global_dtors_aux+0x4f>
10: a1 04 00 00 00 mov 0x4,%eax
15: bb 00 00 00 00 mov $0x0,%ebx
1a: 81 eb 00 00 00 00 sub $0x0,%ebx
20: c1 fb 02 sar $0x2,%ebx
23: 83 eb 01 sub $0x1,%ebx
26: 39 d8 cmp %ebx,%eax
28: 73 1e jae 48 <__do_global_dtors_aux+0x48>
2a: 8d b6 00 00 00 00 lea 0x0(%esi),%esi
30: 83 c0 01 add $0x1,%eax
33: a3 04 00 00 00 mov %eax,0x4
38: ff 14 85 00 00 00 00 call *0x0(,%eax,4)
3f: a1 04 00 00 00 mov 0x4,%eax
44: 39 d8 cmp %ebx,%eax
46: 72 e8 jb 30 <__do_global_dtors_aux+0x30>
48: c6 05 00 00 00 00 01 movb $0x1,0x0
4f: 83 c4 04 add $0x4,%esp
52: 5b pop %ebx
53: 5d pop %ebp
54: c3 ret
55: 8d 74 26 00 lea 0x0(%esi,%eiz,1),%esi
59: 8d bc 27 00 00 00 00 lea 0x0(%edi,%eiz,1),%edi
00000060 <frame_dummy>:
60: 55 push %ebp
61: 89 e5 mov %esp,%ebp
63: 83 ec 18 sub $0x18,%esp
66: a1 00 00 00 00 mov 0x0,%eax
6b: 85 c0 test %eax,%eax
6d: 74 12 je 81 <frame_dummy+0x21>
6f: b8 00 00 00 00 mov $0x0,%eax
74: 85 c0 test %eax,%eax
76: 74 09 je 81 <frame_dummy+0x21>
78: c7 04 24 00 00 00 00 movl $0x0,(%esp)
7f: ff d0 call *%eax
81: c9 leave
82: c3 ret
Disassembly of section .fini:
00000000 <.fini>:
0: e8 fc ff ff ff call 1 <.fini+0x1>
Disassembly of section .init:
00000000 <.init>:
0: e8 5c 00 00 00 call 61 <frame_dummy+0x1>

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swordhui · 发表于 2010-4-18 19:09:03

疑问10, libgcc.a 由gcc提供, 内有一堆o文件,列表如下:

root:/tmp/usr/lib/gcc/i686-pc-linux-gnu/4.4.3# ar t libgcc.a
_muldi3.o
_negdi2.o
_lshrdi3.o
_ashldi3.o
_ashrdi3.o
_cmpdi2.o
_ucmpdi2.o
_clear_cache.o
_enable_execute_stack.o
_trampoline.o
__main.o
_absvsi2.o
_absvdi2.o
_addvsi3.o
_addvdi3.o
_subvsi3.o
_subvdi3.o
_mulvsi3.o
_mulvdi3.o
_negvsi2.o
_negvdi2.o
_ctors.o
_ffssi2.o
_ffsdi2.o
_clz.o
_clzsi2.o
_clzdi2.o
_ctzsi2.o
_ctzdi2.o
_popcount_tab.o
_popcountsi2.o
_popcountdi2.o
_paritysi2.o
_paritydi2.o
_powisf2.o
_powidf2.o
_powixf2.o
_powitf2.o
_mulsc3.o
_muldc3.o
_mulxc3.o
_multc3.o
_divsc3.o
_divdc3.o
_divxc3.o
_divtc3.o
_bswapsi2.o
_bswapdi2.o
_fixunssfsi.o
_fixunsdfsi.o
_fixunsxfsi.o
_fixsfdi.o
_fixdfdi.o
_fixxfdi.o
_fixunssfdi.o
_fixunsdfdi.o
_fixunsxfdi.o
_floatdisf.o
_floatdidf.o
_floatdixf.o
_floatundisf.o
_floatundidf.o
_floatundixf.o
_eprintf.o
__gcc_bcmp.o
_divdi3.o
_moddi3.o
_udivdi3.o
_umoddi3.o
_udiv_w_sdiv.o
_udivmoddi4.o
bid_decimal_globals.o
bid_decimal_data.o
bid_binarydecimal.o
bid_convert_data.o
_isinfd32.o
_isinfd64.o
_isinfd128.o
bid64_noncomp.o
bid128_noncomp.o
bid128_fma.o
bid_round.o
bid_from_int.o
bid64_add.o
bid128_add.o
bid64_div.o
bid128_div.o
bid64_mul.o
bid128_mul.o
bid64_compare.o
bid128_compare.o
bid128.o
bid32_to_bid64.o
bid32_to_bid128.o
bid64_to_bid128.o
bid64_to_int32.o
bid64_to_int64.o
bid64_to_uint32.o
bid64_to_uint64.o
bid128_to_int32.o
bid128_to_int64.o
bid128_to_uint32.o
bid128_to_uint64.o
_addsub_sd.o
_div_sd.o
_mul_sd.o
_eq_sd.o
_ne_sd.o
_lt_sd.o
_gt_sd.o
_le_sd.o
_ge_sd.o
_sd_to_si.o
_sd_to_di.o
_sd_to_usi.o
_sd_to_udi.o
_si_to_sd.o
_di_to_sd.o
_usi_to_sd.o
_udi_to_sd.o
_sd_to_sf.o
_sd_to_df.o
_sd_to_xf.o
_sd_to_tf.o
_sf_to_sd.o
_df_to_sd.o
_xf_to_sd.o
_tf_to_sd.o
_sd_to_dd.o
_sd_to_td.o
_unord_sd.o
_addsub_dd.o
_div_dd.o
_mul_dd.o
_eq_dd.o
_ne_dd.o
_lt_dd.o
_gt_dd.o
_le_dd.o
_ge_dd.o
_dd_to_si.o
_dd_to_di.o
_dd_to_usi.o
_dd_to_udi.o
_si_to_dd.o
_di_to_dd.o
_usi_to_dd.o
_udi_to_dd.o
_dd_to_sf.o
_dd_to_df.o
_dd_to_xf.o
_dd_to_tf.o
_sf_to_dd.o
_df_to_dd.o
_xf_to_dd.o
_tf_to_dd.o
_dd_to_sd.o
_dd_to_td.o
_unord_dd.o
_addsub_td.o
_div_td.o
_mul_td.o
_eq_td.o
_ne_td.o
_lt_td.o
_gt_td.o
_le_td.o
_ge_td.o
_td_to_si.o
_td_to_di.o
_td_to_usi.o
_td_to_udi.o
_si_to_td.o
_di_to_td.o
_usi_to_td.o
_udi_to_td.o
_td_to_sf.o
_td_to_df.o
_td_to_xf.o
_td_to_tf.o
_sf_to_td.o
_df_to_td.o
_xf_to_td.o
_tf_to_td.o
_td_to_sd.o
_td_to_dd.o
_unord_td.o
addtf3.o
divtf3.o
eqtf2.o
getf2.o
letf2.o
multf3.o
negtf2.o
subtf3.o
unordtf2.o
fixtfsi.o
fixunstfsi.o
floatsitf.o
floatunsitf.o
fixtfdi.o
fixunstfdi.o
floatditf.o
floatunditf.o
extendsftf2.o
extenddftf2.o
extendxftf2.o
trunctfsf2.o
trunctfdf2.o
trunctfxf2.o
tf-signs.o
root:/tmp/usr/lib/gcc/i686-pc-linux-gnu/4.4.3

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