Keil Software — A51/AX51/A251 Macro Assembler and Utilities |
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Chapter 9. Linker/Locator
The Lx51 linker/locator is used to link or join together object modules that were |
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created using the Ax51 assembler, the Cx51 compiler, and the Intel PL/M-51 |
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compiler. Object modules that are created by these translators are relocatable |
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and cannot be directly executed. They must be converted into absolute object |
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modules. The Lx51 linker/locator does this and much more. |
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For optimum support of the different 8051 and 251 variants, the following |
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linker/locater variants are available. The LX51 and L251 linker/locater provide |
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an improved memory allocation handling and are supersets of the BL51 |
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linker/locater. The following table gives you an overview of the linker/locater |
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variants along with the translators that are supported. |
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Linker/Locater |
Processes Files from… |
Description |
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BL51 Code |
Keil A51 Macro Assembler |
For classic 8051. Includes support for |
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Banking |
Keil C51 Compiler |
32 x 64KB code banks. |
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Linker/Locater |
Intel ASM51 Assembler |
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Intel PL/M51 Compiler |
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LX51 Extended |
Keil A51 Macro Assembler |
For classic 8051 and extended 8051 |
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Linker/Locater |
Keil C51 Compiler |
versions (Philips 80C51MX, Dallas 390, |
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Keil AX51 Macro Assembler |
etc.) |
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Keil CX51 Compiler for |
Allows code and data banking and |
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80C51MX |
supports up to 16MB code and xdata |
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Intel ASM51 Assembler |
memory. |
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Intel PL/M51 Compiler |
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L251 |
Keil A51 Macro Assembler |
For Intel/Atmel WM 251. |
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Linker/Locater |
Keil C51 Compiler |
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Keil A251 Macro Assembler |
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Keil C251 Compiler |
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Intel ASM51 Assembler |
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Intel PL/M51 Compiler |
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Programs you create using the Ax51 Assembler and the Cx51 Compiler must be linked using the Lx51 linker/locator. You cannot execute or simulate programs that are not linked, even if they consist of only one source module. The Lx51 linker/locator will link one or more object modules together and will resolve references within these modules. This allows you to create a large program that is spread over a number of source files.
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Chapter 9. Linker/Locator |
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The Lx51 linker/locator provides the following functions: |
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Combines several program modules into one module, automatically |
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incorporating modules from the library files |
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Combines relocatable partial segments of the same segment name into a |
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single segment |
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Allocates and manipulates the necessary memory for the segments with |
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which all relocatable and absolute segments are processed |
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Analyzes the program structure and manipulates the data memory using |
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overlay techniques |
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Resolves external and public symbols |
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Defines absolute addresses and computes the addresses of relocatable |
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segments |
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Produces an absolute object file that contains the entire program |
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Produces a listing file that contains information about the Link/Locate |
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procedure, the program symbols, and the cross reference of public and |
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external symbol names |
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Detects errors found in the invocation line or during the Link/Locate run. |
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Supports programs that are larger than 64 Kbytes and applications that are |
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using a Real-Time Multitasking Operating System (RTX51, RTX251, etc.). |
All of these operations are described in detail in the remaining sections of this chapter.
“Overview” on page 257 provides you with a summary of the features and capabilities of the BL51 linker/locator. This chapter introduces the concepts of what a linker is and does.
“Linking Programs” on page 266 describes how to invoke the linker from the command line. The command-line arguments are discussed, and examples are provided.
“Locating Programs to Physical Memory” on page 273 shows how to specify the physical memory available in the target hardware and how to locate segments to specific addresses.
“Data Overlaying” on page 280 explains how the Lx51 linker/locater creates a call tree for segment overlaying of local variables and discusses how to modify this call tree for applications that use indirect program calls.