Microchip Technology XC8 Standard Compiler (Workstation) SW006021-1 SW006021-1 ユーザーズマニュアル
製品コード
SW006021-1
MPLAB
®
XC8 C Compiler User’s Guide
DS52053B-page 204
2012 Microchip Technology Inc.
5.12.3.1
EQUIVALENT ASSEMBLY SYMBOLS
Most C symbols map to an corresponding assembly equivalent.
This mapping is such that an “ordinary” symbol defined in the assembly domain cannot
interfere with an “ordinary” symbol in the C domain. So for example, if the symbol main
is defined in the assembly domain, it is quite distinct to the main symbol used in C code
and they refer to different locations.
interfere with an “ordinary” symbol in the C domain. So for example, if the symbol main
is defined in the assembly domain, it is quite distinct to the main symbol used in C code
and they refer to different locations.
The name of a C function maps to an assembly label that will have the same name, but
with an underscore prepended. So the function main() will define an assembly label
_main
with an underscore prepended. So the function main() will define an assembly label
_main
.
Baseline PIC devices may use alternate assembly domain symbols for functions. The
destinations of call instructions on these devices are limited to the first half of a program
memory page. The compiler, thus, encodes functions in two parts, as illustrated in the
following example of a C function, add(), compiled for a baseline device.
destinations of call instructions on these devices are limited to the first half of a program
memory page. The compiler, thus, encodes functions in two parts, as illustrated in the
following example of a C function, add(), compiled for a baseline device.
entry__add:
LJMP _add
The label entry__add is the function’s entry point and will always be located in a spe-
cial psect linked in the first half of a program memory page. The code associated with
this label is simply a long jump (see Section 6.4.1.4 “Long Jumps and Calls”) to the
actual function body located elsewhere and identified by the label _add.
cial psect linked in the first half of a program memory page. The code associated with
this label is simply a long jump (see Section 6.4.1.4 “Long Jumps and Calls”) to the
actual function body located elsewhere and identified by the label _add.
If you plan to call routines from assembly code, you must be aware of this limitation in
the device and the way the compiler works around it for C functions. Hand-written
assembly code should always call the entry__funcName label rather than the usual
assembly-equivalent function label.
the device and the way the compiler works around it for C functions. Hand-written
assembly code should always call the entry__funcName label rather than the usual
assembly-equivalent function label.
If a C function is qualified static, and there is more than one static function in the
program with exactly the same name, the name of the first function will map to the usual
assembly symbol and the subsequent functions will map to a special symbol with the
form: fileName@functionName, where fileName is the name of the file that
contains the function, and functionName is the name of the function.
program with exactly the same name, the name of the first function will map to the usual
assembly symbol and the subsequent functions will map to a special symbol with the
form: fileName@functionName, where fileName is the name of the file that
contains the function, and functionName is the name of the function.
For example, a program contains the definition for two static functions, both called
add
add
. One lives in the file main.c and the other in lcd.c. The first function will
generate an assembly label _add. The second will generate the label lcd@add.
The name of a non-auto C variable also maps to an assembler label that will have the
same name, but with an underscore prepended. So the variable result will define an
assembly label: _result.
same name, but with an underscore prepended. So the variable result will define an
assembly label: _result.
If the C variable is qualified static, there, again, is a chance that there could be more
than one variable in the program with exactly the same C name. The same rules apply
to non-local static variables as to static functions. The name of the first variable
will map to a symbol prepended with an underscore; the subsequent symbols will have
the form: fileName@variableName, where fileName is the name of the file that
contains the variable, and variableName is the name of the variable.
than one variable in the program with exactly the same C name. The same rules apply
to non-local static variables as to static functions. The name of the first variable
will map to a symbol prepended with an underscore; the subsequent symbols will have
the form: fileName@variableName, where fileName is the name of the file that
contains the variable, and variableName is the name of the variable.
For example a program contains the definition for two static variables, both called
result
result
. One lives in the file main.c and the other in lcd.c. The first function will
generate an assembly label _result. The second will generate the label
lcd@result
lcd@result
.
If there is more than one local static variable (i.e., it is defined inside a function def-
inition) then all the variables will have an assembly name of the form:
functionName@variableName
inition) then all the variables will have an assembly name of the form:
functionName@variableName
. So, if there is a static variable called output in
the function read, and another static variable with the same name defined in the
function update, then in assembly the symbols can be accessed using the symbols
read@output
function update, then in assembly the symbols can be accessed using the symbols
read@output
and update@output, respectively.