问题
For example, I'd like to write something like 'a' instead of 0x61 like I can in C.
The manual mentions them at: https://sourceware.org/binutils/docs/as/Chars.html but without an example I'm not sure I understood.
回答1:
/* 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 $'\n , %al
/* al == 0x0A */
GitHub upstream.
There was actually an example at: https://sourceware.org/binutils/docs-2.25/as/Characters.html :
.byte 74, 0112, 092, 0x4A, 0X4a, 'J, '\J # All the same value.
I dislike this syntax for the following reasons:
- does not play nicely with the C preprocessor:
MACRO($'a)fails because cpp treats'like a char literal. - may generate trailing whitespace as
$', which is hard to observe - not C-like
来源：https://stackoverflow.com/questions/33246811/how-to-use-character-literals-in-gnu-gas-to-replace-numbers