gnu assembler最新官方手册和.macro介绍

最新手册

Top (Using as)Top (Using as)https://sourceware.org/binutils/docs/as/index.html2.38 版本

https://sourceware.org/binutils/docs-2.38/as.pdf

伪指令 .macro 定义，macro可以嵌套，在开源代码中大量使用，需重点关注，官方描述如下

The commands .macro and .endm allow you to define macros that generate assembly output. For example, this definition specifies a macro sum that puts a sequence of numbers into memory:

        .macro  sum from=0, to=5.long   \from.if     \to-\fromsum     "(\from+1)",\to.endif.endm

With that definition, ‘SUM 0,5’ is equivalent to this assembly input:

        .long   0.long   1.long   2.long   3.long   4.long   5

.macro macname ¶

.macro macname macargs … ¶

Begin the definition of a macro called macname. If your macro definition requires arguments, specify their names after the macro name, separated by commas or spaces. You can qualify the macro argument to indicate whether all invocations must specify a non-blank value (through ‘:req’), or whether it takes all of the remaining arguments (through ‘:vararg’). You can supply a default value for any macro argument by following the name with ‘=deflt’. You cannot define two macros with the same macname unless it has been subject to the .purgem directive (see .purgem name) between the two definitions. For example, these are all valid .macro statements:

.macro comm

Begin the definition of a macro called comm, which takes no arguments.

.macro plus1 p, p1

.macro plus1 p p1

Either statement begins the definition of a macro called plus1, which takes two arguments; within the macro definition, write ‘\p’ or ‘\p1’ to evaluate the arguments.

.macro reserve_str p1=0 p2

Begin the definition of a macro called reserve_str, with two arguments. The first argument has a default value, but not the second. After the definition is complete, you can call the macro either as ‘reserve_str a,b’ (with ‘\p1’ evaluating to a and ‘\p2’ evaluating to b), or as ‘reserve_str ,b’ (with ‘\p1’ evaluating as the default, in this case ‘0’, and ‘\p2’ evaluating to b).

.macro m p1:req, p2=0, p3:vararg

Begin the definition of a macro called m, with at least three arguments. The first argument must always have a value specified, but not the second, which instead has a default value. The third formal will get assigned all remaining arguments specified at invocation time.

When you call a macro, you can specify the argument values either by position, or by keyword. For example, ‘sum 9,17’ is equivalent to ‘sum to=17, from=9’.

Note that since each of the macargs can be an identifier exactly as any other one permitted by the target architecture, there may be occasional problems if the target hand-crafts special meanings to certain characters when they occur in a special position. For example, if the colon (:) is generally permitted to be part of a symbol name, but the architecture specific code special-cases it when occurring as the final character of a symbol (to denote a label), then the macro parameter replacement code will have no way of knowing that and consider the whole construct (including the colon) an identifier, and check only this identifier for being the subject to parameter substitution. So for example this macro definition:

   .macro label l
\l:.endm

might not work as expected. Invoking ‘label foo’ might not create a label called ‘foo’ but instead just insert the text ‘\l:’ into the assembler source, probably generating an error about an unrecognised identifier.

Similarly problems might occur with the period character (‘.’) which is often allowed inside opcode names (and hence identifier names). So for example constructing a macro to build an opcode from a base name and a length specifier like this:

   .macro opcode base length\base.\length.endm

and invoking it as ‘opcode store l’ will not create a ‘store.l’ instruction but instead generate some kind of error as the assembler tries to interpret the text ‘\base.\length’.

There are several possible ways around this problem:

Insert white space

If it is possible to use white space characters then this is the simplest solution. eg:

   .macro label l
\l :.endm

Use ‘\()’，The string ‘\()’ can be used to separate the end of a macro argument from the following text. eg:------------开源代码中大量使用，包括固件，内核，出处均来源于此

   .macro opcode base length\base\().\length.endm

Use the alternate macro syntax mode

In the alternative macro syntax mode the ampersand character (‘&’) can be used as a separator. eg:-----------------&作为分隔符

   .altmacro.macro label l
l&:.endm

Note: this problem of correctly identifying string parameters to pseudo ops also applies to the identifiers used in .irp (see .irp symbol,values…) and .irpc (see .irpc symbol,values…) as well.

Another issue can occur with the actual arguments passed during macro invocation: Multiple arguments can be separated by blanks or commas. To have arguments actually contain blanks or commas (or potentially other non-alpha- numeric characters), individual arguments will need to be enclosed in either parentheses (), square brackets [], or double quote " characters. The latter may be the only viable option in certain situations, as only double quotes are actually stripped while establishing arguments. It may be important to be aware of two escaping models used when processing such quoted argument strings: For one two adjacent double quotes represent a single double quote in the resulting argument, going along the lines of the stripping of the enclosing quotes. But then double quotes can also be escaped by a backslash \, but this backslash will not be retained in the resulting actual argument as then seen / used while expanding the macro.

As a consequence to the first of these escaping mechanisms two string literals intended to be representing separate macro arguments need to be separated by white space (or, better yet, by a comma). To state it differently, such adjacent string literals - even if separated only by a blank - will not be concatenated when determining macro arguments, even if they’re only separated by white space. This is unlike certain other pseudo ops, e.g. .ascii.

.endm

Mark the end of a macro definition.

.exitm

Exit early from the current macro definition.

\@

as maintains a counter of how many macros it has executed in this pseudo-variable; you can copy that number to your output with ‘\@’, but only within a macro definition.

LOCAL name [ , … ] ¶

Warning: LOCAL is only available if you select “alternate macro syntax” with ‘--alternate’ or .altmacro. See .altmacro.

arm 有用常用伪指令网址介绍

Useful assembler directives and macros for the GNU assembler - Architectures and Processors blog - Arm Community blogs - Arm Community

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