AN3350 datasheet(81/185 Pages) STMICROELECTRONICS

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AN3350

Working with the ELF linker

Doc ID 018512 Rev 2

81/185

11.3.5

Expressions, variables and integral types

This section describes various expressions, and variable and integral types.

Variables and symbols

Symbol names in a linker command file consists of letters, digits, and underscore

characters. Example 16 shows examples of valid symbol names. Traditionally, symbols

defined inside a linker command file start with an underscore character

Example 16 Valid symbol names

_dec_num = 99999999;

_hex_num_ = 0x9011276;

Expressions and assignments

You can create global symbols and assign addresses to these global symbols using the

standard assignment operator, as shown:

_symbolicname = some_expression;

You must place a semicolon at the end of each assignment statement.

You must place assignments only at the start of an expression. For example, the linker

would reject the following expression:

_sym1 + _sym2 = _sym3;

// ILLEGAL!

When the linker evaluates an expression and assigns it to a variable, the linker gives it either

an absolute or a relocatable type. An absolute expression type is one in which the symbol

contains the value that it will have in the output file. A relocatable expression is one in which

the value is expressed as a fixed offset from the base of a section.

Integer types

The syntax for linker command file expressions is very similar to the syntax of the C

programming language. The linker stores and manipulates integer constants by using 32-bit

signed arithmetic.

Octal integers (commonly known as base eight integers) start with a leading zero, followed

by numerals in the range zero through seven. For example, here are some valid octal

patterns you could put in your linker command file:

●

_octal_number = 01234567;

●

_octal_number2 = 03245;

Decimal integers start with non-zero numeral, followed by numerals in the range of zero

through nine. Here are some examples of valid decimal integers you could put in your linker

command file:

●

_dec_num = 99999999;

●

_decimal_number = 123245;

●

_decyone = 9011276;

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