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An example ARM assembly language module
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Example 7 illustrates some of the core constituents of an assembly language module. The example is written in ARM assembly language.
The constituent parts of this example are:
ELF sections (defined by the
AREAdirective)application entry (defined by the
ENTRYdirective)application execution
application termination
program end (defined by the
ENDdirective).
Example 7 defines
a single section called ARMex that contains code
and is marked as being READONLY.
Example 7. Constituents of an assembly language module
AREA ARMex, CODE, READONLY
; Name this block of code ARMex
ENTRY ; Mark first instruction to execute
start
MOV r0, #10 ; Set up parameters
MOV r1, #3
ADD r0, r0, r1 ; r0 = r0 + r1
stop
MOV r0, #0x18 ; angel_SWIreason_ReportException
LDR r1, =0x20026 ; ADP_Stopped_ApplicationExit
SVC #0x123456 ; ARM semihosting (formerly SWI)
END ; Mark end of file
Application entryThe ENTRY directive declares an entry point to
the program. It marks the first instruction to be executed. In applications
using the C library, an entry point is also contained within the
C library initialization code. Initialization code and exception
handlers also contain entry points.
The application code in Example 7 begins executing at the label start,
where it loads the decimal values 10 and 3 into registers R0 and R1.
These registers are added together and the result placed in R0.
After executing the main code, the application terminates
by returning control to the debugger. This is done using the ARM
semihosting SVC (0x123456 by default), with the
following parameters:
R0 equal to
angel_SWIreason_ReportException(0x18)R1 equal to
ADP_Stopped_ApplicationExit(0x20026).
The END directive instructs the assembler to
stop processing this source file. Every assembly language source
module must finish with an END directive on a line
by itself. Any lines following the END directive are
ignored by the assembler.
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| Non-Confidential | ID062912 |
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