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5.3.1 LINKING use .net framework pdf 417 integration todeploy pdf417 for .net Microsoft Office Word Website In combining the sep PDF417 for .NET arately compiled or assembled modules into a load module, the linker must: Resolve address references that are external to modules as it links them. Relocate each module by combining them end-to-end as appropriate.

During this relocation process many of the addresses in the module must be changed to reflect their new location. Specify the starting symbol of the load module. If the memory model includes more than one memory segment, the linker must specify the identities and contents of the various segments.

Resolving external references In resolving address references the linker needs to distinguish local symbol names (used within a single source module) from global symbol names (used in more than one module). This is accomplished by making use of the .global and .

extern pseudo-ops during assembly. The .global pseudo-op instructs the assembler to mark a symbol as being available to other object modules during the linking phase.

The .extern pseudo-op identi es a label that is used in one module but is de ned in another. A .

global is thus used in the module where a symbol is de ned (such as where a subroutine is located) and a .extern is used in every other module that refers to it. Note that only address labels can be.

LANGUAGES AND THE MACHINE global or external: .NET barcode pdf417 it would be meaningless to mark a .equ symbol as global or external, since .

equ is a pseudo-op that is used during the assembly process only, and the assembly process is completed by the time that the linking process begins. All labels referred to in one program by another, such as subroutine names, will have a line of the form shown below in the source module:. .global symbol1, symbol2, ..

.. All other labels PDF417 for .NET are local, which means the same label can be used in more than one source module without risking confusion since local labels are not used after the assembly process nishes. A module that refers to symbols de ned in another module should declare those symbols using the form:.

.extern symbol1, symbol2, ..

.. As an example of Visual Studio .NET pdf417 how .global and .

extern are used, consider the two assembly code source modules shown in Figure 5-6. Each module is separately assem! Main program .begin .

org 2048 .extern sub [x], %r2 main: ld ld [y], %r3 call sub jmpl %r15 + 4, %r0 x: 105 y: 92 .end.

Figure 5-6. ! Subroutine libr .net vs 2010 PDF 417 ary .begin .

equ 1 .org 2048 .global sub sub: orncc %r3, %r0, %r3 addcc %r3, ONE, %r3 jmpl %r15 + 4, %r0 .

end ONE. A program calls a subroutine that subtracts two integers. bled into an obje .net vs 2010 pdf417 2d barcode ct module, each with its own symbol table as shown in Figure 5-7. The symbol tables have an additional eld that indicates if a symbol is global or external.

Program main begins at location 2048, and each instruction is four bytes long, so x and y are at locations 2064 and 2068, respectively. The symbol sub is marked as external as a result of the .extern pseudo-op.

As part of the assembly process the assembler includes header information in the module about symbols that are global and external so they can be resolved at link time.. LANGUAGES AND THE MACHINE Symbol sub main x y Value 2048 2064 2068 Global/ RelocExternal atable External No No No Yes Yes Yes Symbol ONE sub Value 1 2048 Global/ RelocExternal atable No Global No Yes Subroutine Library Main Program Figure 5-7 Symbol .net vs 2010 pdf417 2d barcode tables for the assembly code source modules shown in Figure 5-6..

Relocation Notice in Figure 5-6 that the two programs, main and sub, both have the same starting address, 2048. Obviously they cannot both occupy that same memory address. If the two modules are assembled separately there is no way for an assembler to know about the con icting starting addresses during the assembly phase.

In order to resolve this problem, the assembler marks symbols that may have their address changed during linking as relocatable, as shown in the Relocatable elds of the symbol tables shown in Figure 5-7. The idea is that a program that is assembled at a starting address of 2048 can be loaded at address 3000 instead, for instance, as long as all references to relocatable addresses within the program are increased by 3000 2048 = 952. Relocation is performed by the linker so that relocatable addresses are changed by the same amount that the loading origin is changed, but absolute, or non-relocatable addresses (such as the highest possible stack address, which is 231 4 for 32-bit words) stays the same regardless of the loading origin.

The assembler is responsible for determining which labels are relocatable when it builds the symbol table. It has no meaning to call an external label relocatable, since the label is de ned in another module, so sub has no relocatable entry in the symbol table in Figure 5-7 for program main, but it is marked as relocatable in the subroutine library. The assembler must also identify code in the object module that needs to be modi ed as a result of relocation.

Absolute numbers, such as constants (marked by .equ ,or that appear in memory locations, such as the contents of x and y, which are 105 and 92, respectively) are not relocatable. Memory locations that are positioned relative to a .

org statement, such as x and y (not the contents of x and y!) are generally relocatable. References to xed locations, such as a permanently resident graphics routine that may be hardwired into the machine, are not relocatable. All of the information needed to relocate a.

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