我试图在编译后优化精灵的大小。
但是在printf中声明的字符串被移动到.rodata部分，并且不会被链接器优化。
#include <stdio.h>
#include <stdlib.h>
static char str1[] = "String1"; //goto .data.str1
const char str2[] = "String2"; //goto .rodata.str2
int main(){
printf("%s",str1); //"%s" in .rodata
printf("%s",str2);
printf("On-the fly string"); //goto .rodata
return 0;
}
void unused_function(){
const char str3[] = "String Not Used"; //goto .text.unused_function and is removed by the linker
printf("I would like to optimize this string"); //goto .rodata and isn't removed by the linker
printf("%s", str3); //
}
我编译并链接这些参数：
gcc -fdata-sections -ffunction-sections -Wl,--gc-sections hello.c -o hello.out
这是在编译之后：
Contents of section .data.str1:
0000 53747269 6e673100 String1.
Contents of section .rodata.str2:
0000 53747269 6e673200 String2.
Contents of section .rodata:
0000 2573004f 6e2d7468 6520666c 79207374 %s.On-the fly st
0010 72696e67 00000000 4920776f 756c6420 ring....I would
0020 6c696b65 20746f20 6f707469 6d697a65 like to optimize
0030 20746869 73207374 72696e67 00 this string.
Contents of section .text.main:
0000 554889e5 be000000 00bf0000 0000b800 UH..............
0010 000000e8 00000000 be000000 00bf0000 ................
0020 0000b800 000000e8 00000000 bf000000 ................
0030 00b80000 0000e800 000000b8 00000000 ................
0040 5dc3 ].
Contents of section .text.unused_function:
0000 554889e5 4883ec20 64488b04 25280000 UH..H.. dH..%(..
0010 00488945 f831c048 b8537472 696e6720 .H.E.1.H.String
0020 4e488945 e048b86f 74205573 65640048 NH.E.H.ot Used.H
0030 8945e8bf 00000000 b8000000 00e80000 .E..............
0040 0000488d 45e04889 c6bf0000 0000b800 ..H.E.H.........
0050 000000e8 00000000 488b45f8 64483304 ........H.E.dH3.
0060 25280000 007405e8 00000000 c9c3 %(...t........
和链接后
Contents of section .text:
400440 31ed4989 d15e4889 e24883e4 f0505449 1.I..^H..H...PTI
400450 c7c0e005 400048c7 c1700540 0048c7c7 ....@.H..p.@.H..
400460 2d054000 e8b7ffff fff4660f 1f440000 -.@.......f..D..
400470 b83f1060 0055482d 38106000 4883f80e .?.`.UH-8.`.H...
400480 4889e577 025dc3b8 00000000 4885c074 H..w.]......H..t
400490 f45dbf38 106000ff e00f1f80 00000000 .].8.`..........
4004a0 b8381060 0055482d 38106000 48c1f803 .8.`.UH-8.`.H...
4004b0 4889e548 89c248c1 ea3f4801 d048d1f8 H..H..H..?H..H..
4004c0 75025dc3 ba000000 004885d2 74f45d48 u.]......H..t.]H
4004d0 89c6bf38 106000ff e20f1f80 00000000 ...8.`..........
4004e0 803d510b 20000075 11554889 e5e87eff .=Q. ..u.UH...~.
4004f0 ffff5dc6 053e0b20 0001f3c3 0f1f4000 ..]..>. ......@.
400500 48833d18 09200000 741eb800 00000048 H.=.. ..t......H
400510 85c07414 55bf200e 60004889 e5ffd05d ..t.U. .`.H....]
400520 e97bffff ff0f1f00 e973ffff ff554889 .{.......s...UH.
400530 e5be3010 6000bff8 054000b8 00000000 ..0.`....@......
400540 e8cbfeff ffbef005 4000bff8 054000b8 ........@....@..
400550 00000000 e8b7feff ffbffb05 4000b800 ............@...
400560 000000e8 a8feffff b8000000 005dc390 .............]..
400570 41574189 ff415649 89f64155 4989d541 AWA..AVI..AUI..A
400580 544c8d25 88082000 55488d2d 88082000 TL.%.. .UH.-.. .
400590 534c29e5 31db48c1 fd034883 ec08e83d SL).1.H...H....=
4005a0 feffff48 85ed741e 0f1f8400 00000000 ...H..t.........
4005b0 4c89ea4c 89f64489 ff41ff14 dc4883c3 L..L..D..A...H..
4005c0 014839eb 75ea4883 c4085b5d 415c415d .H9.u.H...[]A\A]
4005d0 415e415f c366662e 0f1f8400 00000000 A^A_.ff.........
4005e0 f3c3 ..
Contents of section .rodata:
4005f0 53747269 6e673200 2573004f 6e2d7468 String2.%s.On-th
400600 6520666c 79207374 72696e67 00000000 e fly string....
400610 4920776f 756c6420 6c696b65 20746f20 I would like to
400620 6f707469 6d697a65 20746869 73207374 optimize this st
400630 72696e67 00 ring.
Contents of section .data:
601030 53747269 6e673100 String1.
因此你可以看到函数＆＃34; unused_function（）＆＃34;并且声明为const的字符串被删除但我想删除最后一个字符串＆＃34;我想优化这个字符串＆＃34;
可以使用-fmerge-constants轻松删除第一个示例，因为printf中的字符串将根据其长度放入一个部分，但如果2个字符串具有相同的长度并且使用了一个，则它将不起作用。 / p>
#include <stdio.h>
#include <stdlib.h>
void used_function();
static char str1[] = "String1"; //goto .data.str1 const char str2[] = "String2"; //goto .rodata.str2
int main(){
printf("%s",str1); //"%s" in .rodata printf("%s",str2); printf("On-the fly string"); //goto .rodata
used_function();
return 0;
}
void unused_function(){
const char str3[] = "String Not Used"; //goto .text.unused_function and is removed by the linker
printf("I would like to optimize this string 1"); //goto .rodata.str1.8 and isn't removed by the linker
printf("%s", str3); // }
void used_function(){
printf("A string used here with the same size 2"); //goto .rodata.str1.8 }
用-O2
编译链接后Contents of section .rodata:
400640 2573004f 6e2d7468 6520666c 79207374 %s.On-the fly st
400650 72696e67 00000000 41207374 72696e67 ring....A string
400660 20757365 64206865 72652077 69746820 used here with
400670 74686520 73616d65 2073697a 65203200 the same size 2.
400680 4920776f 756c6420 6c696b65 20746f20 I would like to
400690 6f707469 6d697a65 20746869 73207374 optimize this st
4006a0 72696e67 20310000 53747269 6e673200 ring 1..String2.
字符串仍然在这里！
答案 0 :(得分：4)
使用编译器选项-O2来优化二进制文件。这将消除仅由未调用的unused_function引用的字符串。
答案 1 :(得分：0)
我刚刚发现这是GCC的一个错误，但尚未得到解决。