如何在 gcc 中禁用编译器优化？

我正在努力学习汇编语言。我已经搜索并找到了如何反汇编一个 .c文件，但我认为它产生了一些优化版本的程序。有没有什么方法可以让我看到对应于我的 C 文件的确切汇编代码。

131491 次浏览
小开
最佳答案

The gcc option -O enables different levels of optimization. Use -O0 to disable them and use -S to output assembly. -O3 is the highest level of optimization.

Starting with gcc 4.8 the optimization level -Og is available. It enables optimizations that do not interfere with debugging and is the recommended default for the standard edit-compile-debug cycle.

To change the dialect of the assembly to either intel or att use -masm=intel or -masm=att.

You can also enable certain optimizations manually with -fname.

Have a look at the gcc manual for much more.

小开

Use the command-line option -O0 (-[capital o][zero]) to disable optimization, and -S to get assembly file. Look here to see more gcc command-line options.

小开

You can disable optimizations if you pass -O0 with the gcc command-line.

E.g. to turn a .C file into a .S file call:

gcc -O0 -S test.c

小开

For gcc you want to omit any -O1 -O2 or -O3 options passed to the compiler or if you already have them you can append the -O0 option to turn it off again. It might also help you to add -g for debug so that you can see the c source and disassembled machine code in your debugger.

See also: http://sourceware.org/gdb/onlinedocs/gdb/Optimized-Code.html

小开

To test without copy elision and see you copy/move constructors/operators in action add "-fno-elide-constructors".

Even with no optimizations (-O0 ), GCC and Clang will still do copy elision, which has the effect of skipping copy/move constructors in some cases. See this question for the details about copy elision.

However, in Clang 3.4 it does trigger a bug (an invalid temporary object without calling constructor), which is fixed in 3.5.

小开

Long time ago, but still needed.

info - https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html
list - gcc -Q --help=optimizers test.c | grep enabled
disable as many as you like with:
gcc **-fno-web** -Q --help=optimizers test.c | grep enabled
小开

You can also control optimisations internally with #pragma GCC push_options

#pragma GCC push_options
/* #pragma GCC optimize ("unroll-loops") */


.... code here .....


#pragma GCC pop_options

提交答案