gcc的窗户上产生的垃圾？窗户VS Linux的 [英] gcc on windows generating garbage? windows vs linux
问题描述
我试图找出为什么窗口有比Linux同一节目这么多的指令。
所以我只是用 int类型的= 0xbeef; 和的printf（测试\\ n）; C和编译Linux和Windows。当我调试，拆卸主框架，我得到这个：
在Linux上：
I'm trying to find out why in windows has so much more instructions for the same program than linux.
So I just used int a=0xbeef; and printf("test\n"); in C and compiled in Linux and Windows. When I debug and disassembly the main frame I got this:
On linux:
0x080483e4 <+0>: push %ebp
0x080483e5 <+1>: mov %esp,%ebp
0x080483e7 <+3>: and $0xfffffff0,%esp
0x080483ea <+6>: sub $0x20,%esp
0x080483ed <+9>: movl $0xbeef,0x1c(%esp)
0x080483f5 <+17>: movl $0x80484d0,(%esp)
0x080483fc <+24>: call 0x8048318 <puts@plt>
0x08048401 <+29>: leave
0x08048402 <+30>: ret
好吧这很好。我看到MOVL为0x1c ESP的偏移把价值在那里。
Ok that's nice. I see the movl 0x1c offset of esp to put the value there.
但在Windows我得到这个：
But in windows I got this:
0x401290 <main>: push %ebp
0x401291 <main+1>: mov %esp,%ebp
0x401293 <main+3>: sub $0x18,%esp
0x401296 <main+6>: and $0xfffffff0,%esp
0x401299 <main+9>: mov $0x0,%eax
0x40129e <main+14>: add $0xf,%eax
0x4012a1 <main+17>: add $0xf,%eax
0x4012a4 <main+20>: shr $0x4,%eax
0x4012a7 <main+23>: shl $0x4,%eax
0x4012aa <main+26>: mov %eax,0xfffffff8(%ebp)
0x4012ad <main+29>: mov 0xfffffff8(%ebp),%eax
0x4012b0 <main+32>: call 0x401720 <_alloca>
0x4012b5 <main+37>: call 0x4013c0 <__main>
0x4012ba <main+42>: movl $0xbeef,0xfffffffc(%ebp)
0x4012c1 <main+49>: movl $0x403000,(%esp,1)
0x4012c8 <main+56>: call 0x401810 <printf>
0x4012cd <main+61>: mov $0x0,%eax
0x4012d2 <main+66>: leave
0x4012d3 <main+67>: ret
首先，我不知道为什么在Windows编译器（MinGW的）产生大量code。为2x比Linux更多...这让我思考。而另一件事：从主+ 9〜+主我37无法看到，code点
First of all, I don't know why the windows compiler (mingw) generate so much code. Is 2x more than Linux... this makes me thinking. And another thing: from main+9 to main+37 I can't see the point of that code.
如果有人回答这个我要感谢，我只是好奇：）
I would thank if someone answer to this, I'm just curious :)
编辑：
在Linux上-O3说法我得到了相同的和Windows类似魔术happends：
edit: With -O3 argument on linux I got the same and in windows something like magic happends:
0x401290 <main>: push %ebp
0x401291 <main+1>: mov $0x10,%eax
0x401296 <main+6>: mov %esp,%ebp
0x401298 <main+8>: sub $0x8,%esp
0x40129b <main+11>: and $0xfffffff0,%esp
0x40129e <main+14>: call 0x401700 <_alloca>
0x4012a3 <main+19>: call 0x4013a0 <__main>
0x4012a8 <main+24>: movl $0x403000,(%esp,1)
0x4012af <main+31>: call 0x4017f0 <puts>
0x4012b4 <main+36>: leave
0x4012b5 <main+37>: xor %eax,%eax
0x4012b7 <main+39>: ret
离开的话，那么异RET。 OK：D调用_alloca并调用__main仍然存在。我不知道什么是 0x401291＆lt;主+ 1计算值：MOV $ 0×10，％eax中在这里做什么：D
推荐答案
您好像老3.x系列被编译 GCC ，你最好升级。较新的版本不调用的alloca 。我怀疑的alloca 的特定版本可能会使用寄存器约定，以便在 MOV为0x10，％EAX 可能是设置参数该呼叫。
You seem to be compiling with old 3.x series gcc, you'd better upgrade. Newer versions don't invoke alloca. I suspect the particular version of alloca might use register convention so the mov 0x10,%eax is probably setting up the argument for that call.
__主是 crtbegin.o 定义的启动函数执行全局构造并注册使用功能 atexit对将运行全局销毁。
__main is a startup function defined in crtbegin.o that executes global constructors and registers a function using atexit that will run the global destructors.
另外请注意，主得到特殊待遇，如堆栈对齐code和上述的初始化。这可能是一个好主意，而不是比较纯的功能，如果你是在code生成问题只是感兴趣。
Also note that main gets special treatment, like the stack alignment code and the above-mentioned initialization. It may be a good idea to instead compare a "plain" function if you are just interested in code generation issues.
这篇关于gcc的窗户上产生的垃圾？窗户VS Linux的的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
