GNU ARM Assembler pseudo-directive (assembler directives)

Source: Internet
Author: User
1. Introduction to the GNU ARM Assembly

Any assembly line is structured as follows: [<label>:] [<instruction or DIRECTIVE>} @ Comment
[< label;:] [< instruction;} @ Comment

In the GNU ARM assembly, any end of a colon is considered to be a label, not necessarily the beginning of a line. Here is a simple example of the assembler that defines an "add" function that returns the two parameters and:[CPP]View plain Copy. Section. Text, "X". Global add @ give the symbol add external linkage add:                                    Add R0, R0, r1 @ Add input arguments MOV pc, LR @ return from subroutine @ End of Program
2. GNU Arm Assembly pseudo-directive

GNU Arm Assembly pseudo-directives all begin with. Common Assembly pseudo-means are as follows:

Assembly Pseudo-Directives Describe Example
. ASCII "<string>" Inserts a string into the destination file, but does not end with null . ASCII "JNZ" @ Insert byte 0x4a 0x4E 0x5A
. Asciz "<string>" Similar to. ASCII, but ends with null . Asciz "JNZ" @ Insert byte 0x4a 0x4E 0x5A 0x00
. balign <power_of_2>
{, <max_padding>}}
Make the following position <power_of_2> align . Byte 0x55 @ Insert byte: 0x55
. balign 4,0 @ Insert 3 aligned bytes: 0x00 0x00 0x00
. Word 0xaa55ee11 @ Insert byte: 0x11 0xEE 0x55 0xAA (LSB order)
. Byte <byte1> {, <byte2>} ... Insert byte to destination file . Byte, ' A ' @ Inserts the bytes 0x40 0x41
. Byte 0x42 @ Inserts the byte 0x42
. Byte 0b1000011, 0104 @ Inserts the bytes 0x43 0x44
. Code <number_of_bits> Set the number of instruction bits, 16-bit thumb or 32-bit arm . code 16 @ Set the following assembly as thumb instructions
. else Use with. if and. endif
. end End of symbol assembly file, assembler no longer reads back content
. endif If used in conjunction with the.
. endm Flag macro definition end, used in conjunction with. macro
. Endr End a loop, using the. rept and. IRP
. equ <symbol Name>, <value> Set the value of a symbol . Equ Adams, (5 * 8) + 2 @ set Adams to 42
. Set Adams, 0x2A @ set Adams to 42
Adams = 0b00101010 @ set Adams to 42
. err Assembly when you encounter. Err, stop compiling
. exitm Exit macro Definition Halfway
. Global <symbol> Identity symbol is accessed by other modules of the program (assembly or C),
Equivalent to Export_symbol in kernel
. Global _my_test_count @ It can be r/w by other modules
. Hword <short1> {, <short2>}
Insert 16-bit (half-character) value to the destination file . Hword 0xaa55, 12345 @ Insert byte 0x55 0xAA 0x39 0x30
.2byte 0X55AA, 1 @ Insert byte 0xAA 0x55 0xFF 0xFF
@ Least significant Byte (LSB) ordering assumed
. If <logical_expression> Use with. endif
. ifdef <symbol> Use with. endif
. ifndef <symbol> Use with. endif
. include "<filename>" Similar to C's # include
. IRP <param> {, <val_1>}
{, <val_2>} ...
Repeats a block of code, once for each value
In the value list. Mark the end of the block
Using a. endr directive. In the repeated code block,
Use \<param> to substitute the associated
value in the Value list.
. macro <name> {<arg_1}
{, <arg_2>} ... {, <arg_n>}
Define a compilation macro called Name, which has n parameters,
and must end with. Endm.
. macro Shiftleft A, b
. If \b < 0
MOV \a, \a, ASR #-\b
. exitm
. endif
MOV \a, \a, LSL #\b
. endm
. Section <section_name>
{, "<flags>"}
To start a new section, the Section_name can be:
. Text: Code snippet
. Data: Initialized Segments
. BSS: Uninitialized data segments
The flags can be:
A allowable section
W writable section
X executable section
. section. Text, "X"
. set <variable_name>,
Sets the value of the change, as with the. equ . Set Adams, 0x2A @ set Adams to 42
. Space <number_of_bytes>
{, <fill_byte>}
Reserve a given byte space and set to 0 or fill_byte . Space 0x400,0
. Word <word1> {, <word2>} ... Insert a 32-bit word list to the destination file Head_ptr:. Word 0 @ Head pointer to within buffer (initially zero)
Tail_ptr:. Word 0 @ tail pointer to within buffer (initially zero)
. Word 0xDEADBEEF @inserts the bytes 0xEF 0xBE 0xAD 0xDE
.4byte-42 @ Inserts the bytes 0xd6 0xFF 0xFF 0xFF
@ Least significant Byte (LSB) ordering assumed
. rept <number_of_times> Repeat code block number_of_times times, with C for
Similar to the end of Endr
<register_name>. req
Register Rename Acc. req R0

3. Arm special characters and syntax

@ Comment symbols in line of code
# Full line Comment symbol
; Statement Detach symbol
#或 $ Prefix of direct operand
. arm
assembly using ARM directives
. Thumb
Assembly using Thumb Instructions
. code16
Assembly using Thumb Instructions
. code32
assembly using ARM directives
. force_thumb
Force use of thumb mode even if not supported
. thumb_func
Mark entry point as thumb coded (Force BX entry)
. ltorg
Start a new literal pool (text pool: an area embedded in code to hold constants)

0 8 binary
0x or 0X 16 binary
0b or 0 B Binary
No leader character 10 binary

. Data Identifies the subsequent statement into the destination file data segment
. text
Identifies the code snippet that puts the subsequent statement into the destination file
. extern symbol
Introduce symbols from other modules, like extern in C
. Skip Expression
The number of bytes specified by skip expression in the destination file
Buffer:. Skip @Buffer of bytes, uninitialised

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