如何在GNU GAS中使用字符文字替换数字? [英] How to use character literals in GNU GAS to replace numbers?

问题描述

例如，我想写像'a'这样的东西，而不是像我在C语言中那样写的东西.

For example, I'd like to write something like 'a' instead of 0x61 like I can in C.

手册在以下位置提及了它们: https://sourceware.org/binutils/docs/as/Chars.html ，但如果没有示例，我不确定我是否理解.

The manual mentions them at: https://sourceware.org/binutils/docs/as/Chars.html but without an example I'm not sure I understood.

推荐答案

/* Immediate. Without the `$`, does a memory access, and segfaults! */
mov $'a, %al
/* al == 0x61 */

/* Memory. */
mov c, %al
/* al == 0x62 */

c: .byte 'b

/* Space character works. */
mov $' , %al
/* al == 0x20 */

/* Backslash escapes work. */
mov $'\n , %al
/* al == 0x0A */

GitHub上游.

实际上有一个示例: https://sourceware.org/binutils/docs-2.25/as/Characters.html :

.byte  74, 0112, 092, 0x4A, 0X4a, 'J, '\J # All the same value.

由于以下原因，我不喜欢这种语法:

I dislike this syntax for the following reasons:

• 在C预处理器上不能很好地发挥作用:MACRO($'a)失败，因为cpp将'视为char文字.
• 可能会生成$'的尾随空格，这很难观察
• 不像C的

• does not play nicely with the C preprocessor: MACRO($'a) fails because cpp treats ' like a char literal.
• may generate trailing whitespace as $', which is hard to observe
• not C-like

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