GNU ARM Asmbler Quick Reference
A summary of uful commands and expressions for the ARM architecture using the GNU asmbler is prented briefly in the concluding portion of this Appendix. Each asmbly line has the following format: [<label>:] [<instruction or directive>} @ comment
Unlike the ARM asmbler, using the GNU asmbler does not require you to indent instructions and directives. Labels are recognized by the following colon instead of their position at the start of a line. An example follows showing a simple asmbly program defining a function ‘add’ that returns the sum of two input arguments:
.ction .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
GNU Asmbler Directives for ARM
The follow is an alphabetical listing of the more command GNU asmbler directives.
GNU Asmbler Directive Description
.ascii “<string>” Inrts the string as data into the asmbly (like DCB in
armasm).
.asciz “<string>” Like .ascii, but follows the string with a zero byte.
.balign <power_of_2> {,<fill_value>
{,<max_padding>} } Aligns the address to <power_of_2> bytes. The asmbler aligns by adding bytes of value <fill_value> or a suitable default. The alignment will not occur if more than <max_padding> fill bytes are required (similar to ALIGN in armasm).蓝牙耳机使用
.byte <byte1> {,<byte2>} … Inrts a list of byte values as data into the asmbly (like DCB
in armasm).
.code <number_of_bits> Sets the instruction width in bits. U 16 for Thumb and 32 for
初中生自我评价ARM asmbly (similar to CODE16 and CODE32 in armasm). .el U with .if and .endif (similar to ELSE in armasm).
.end Marks the end of the asmbly file (usually omitted).
.endif Ends a conditional compilation code block – e .if, .ifdef, .ifndef
(similar to ENDIF in armasm).
.endm Ends a macro definition – e .macro (similar to MEND in
armasm).
.endr Ends a repeat loop – e .rept and .irp (similar to WEND in
湿咸西游记
armasm).
.equ <symbol name>, <value> This directive ts the value of a symbol (similar to EQU in
armasm)
.err Caus asmbly to halt with an error.
.exitm Exit a macro partway through – e .macro (similar to MEXIT in
armasm)
.global <symbol> This directive gives the symbol external linkage (similar to
EXPORT in armasm).
.hword <short1> {,<short2>} … Inrts a list of 16-bit values as data into the asmbly (similar to DCW in armasm).
GNU Asmbler Directive Description
.if <logical_expression> Makes a block of code conditional. End the block using .endif
手表十大品牌(similar to IF in armasm). See also .el.
.ifdef <symbol> Include a block of code if <symbol> is defined. End the block
with .endif.
.ifndef <symbol> Include a block of code if <symbol> is not defined. End the block
with .endif.
.include “<filename>” Includes the indicated source file (similar to INCLUDE in
armasm or #include in C).
.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, u \<param> to substitute the associated value in the value list.
.macro <name> {<arg_1} {,<arg_2>} … {,<arg_N>} Defines an asmbler macro called <name> with N parameters. The macro definition must end with .endm. To escape from the macro at an earlier point, u .exitm. The directives are similar to MACRO, MEND, and MEXIT in armasm. You must precede the dummy macro parameters by \. For example:
.macro SHIFTLEFT a, b
.if \b < 0
MOV \a, \a, ASR #-\b
.exitm
.endif
定做蛋糕
MOV \a, \a, LSL #\b
.endm
.rept <number_of_times> Repeats a block of code the given number of times. End with
.endr.
<register_name> .req <register_name> This directive names a register. It is similar to the RN directive in armasm except that you must supply a name rather than a number on the right (e.g., acc .req r0).
.ction <ction_name> {,”<flags>”} Starts a new code or data ction. Sections in GNU are called .
text, a code ction, .data, an initialized data ction, and .bss, an uninitialized data ction. The ctions have default flags, and the linker understands the default names (similar directive to the armasm directive AREA). The following are allowable .ction flags for ELF format files:
<Flag> Meaning
a allowable ction
w writable ction
x executable ction
.t <variable_name>, <variable_value> This directive ts the value of a variable. It is similar to SETA in armasm.
.space <number_of_bytes> {,<fill_byte>} Rerves the given number of bytes. The bytes are filled with zero or <fill_byte> if specified (similar to SPACE in armasm).
.word <word1> {,<word2>} … Inrts a list of 32-bit word values as data into the asmbly
(similar to DCD in armasm).
Asmbler Special Characters / Syntax
Inline comment char: ‘@’
Line comment char: ‘#’
Statement
parator: ‘;’
Immediate operand prefix: ‘#’ or ‘$’
Register Names
General registers: %r0 - %r15 ($0 = const 0)
FP registers: %f0 - %f7
Non-saved (temp) regs: %r0 - %r3, %r12
Saved registers: %r4 - %r10
Stack ptr register: %sp
Frame ptr register: %fp
Link (retn) register: %lr
Program counter: %ip
Status register: $psw
Status register flags: xPSR
约旦
(x = C current) xPSR_all
(x = S saved ) xPSR_f
xPSR_x
xPSR_ctl
xPSR_fs xPSR_fx xPSR_fc xPSR_cs xPSR_cf xPSR_cx .. and so on
Arm Procedure Call Standard (APCS) Conventions
节约用水内容
Argument registers: %a0 - %a4 (aliad to %r0 - %r4)
货车超重罚款标准Returned value regs: %v1 - %v6 (aliad to %r4 - %r9)
Addressing Modes
‘rn’ in the following refers to any of the numbered registers, but not the control registers.
addr Absolute addressing mode
%rn Register direct
[%rn] Register indirect or indexed
[%rn,#n] Register bad with offt
#imm Immediate data
Machine Dependent Directives
.
arm Asmble using arm mode
.thumb Asmble using thumb mode
.code16 Asmble using thumb mode
.code32 Asmble using arm mode
.force_thumb Force thumb mode (even if not supported)
.thumb_func Mark entry point as thumb coded (force bx entry)
.ltorg Start a new literal pool
Opcodes
For detailed information on the machine instruction t, e this manual:
ARM Architecture Reference Manual , Addison-Wesley ISBN 0-201-73719-1
Here is a recommended book to get a lot of system developer information on the ARM architecture.
ARM System Developer’s Guide , Morgan Kaufmann Publishers ISBN 1-55860-874-5 (alk.paper), authors: Andrew N. Sloss, Dominic Symes, Chris Wright, 2004
