Commenting syntax for x86 AT&T syntax assembly
Solution 1
Comments for at&t assembler are:
# this is a comment
/* this is a comment */
According to the fourth result Google gave me
//
and /* */
comments are only supported in .S
files because GCC runs the C preprocessor on them before assembling. For .s
files, the actual assembler itself (as
) only handles #
as a comment character, for x86.
For some other ISAs, GAS uses other comment characters, for example @
for ARM.
Solution 2
GNU AS Comments
The following are handled by as
directly. (Not the C preprocessor.)
-
#
Comments - Works as a "rest of line" comment.Important Caveat:
#
is also the GCC preprocessor directive symbol. The preprocessor runs first, so this means that if you are running it,# include comments in your code to get full credit
at the beginning of the line (whitespaces don't count) will give you
error: #include expects "FILENAME" or <FILENAME>
with gcc, even with a space after the#
.However, these are case-sensitive, so capitalizing
# Include
actually works:# Include comments in your code to get full credit
While it is generally good practice to capitalize the first letter of your comments anyway, you can use
##
as a just-in-case measure. (Just don't use it on any lines that are part of a#define
macro because##
is also the token pasting operator.) -
/
comments - Start of line commentThese may only be used at the start of a line (after whitespace removal).
/ This is OK xor %eax, %eax / This is *not* ok
C-style Comments (preprocessor)
These work if the C preprocessor is run on the source file.
In most architectures, the following are supported:
-
// Rest of line comment
works pretty much as you'd expect from C.In rare cases this causes problems with
.
pseudo-ops. To work around this, I just use a block comment or just move the comment to the preceding line. -
/* Use this for block comments */
. I currently haven't run into any issues with this.
So what do I use?
- If you're not allowed to preprocess everything, choose one of the GNU AS Comment styles,
#
or/
. - If you're sure you will preprocess everything, it may be safer to go with the C-style comments
//
and/**/
to avoid preprocessor issues. However, if you keep in mind the hidden gotchas, you should be ok. - If you're concerned about having to handle both, choose either
/
or##
so you don't have to worry about the preprocessor or lack thereof on any one file.##
is more versatile, but may lead to messier code. - Whatever the case may be, choose one and be consistent.
Solution 3
Try # or // or /* */. Might work
Comments
-
ihsoy ih almost 2 years
The Intel syntax has comments using the semicolon. When I switched to AT&T, it actually tried to interpret the comments.
What is the comment syntax for AT&T assembly?