Porting Enterprise Apps from UNIX to Linux

By Martyn Honeyford
2005-04-17

Architecture-Specific Changes

Architecture-specific code in an application is typically limited to a few areas. I'll look at some examples in this section.

Determining endian-ness
The programmer does not have to worry about which architecture the code being written for. Linux provides a way to determine the endian-ness in /usr/include/endian.h. Following is a typical code snippet you can use to determine if the operating environment is big- or little-endian; you can set a specific flag for your convenience.

/• Are we big-endian? •/

#include <endian.h>

#if  __BYTE_ORDER == __LITTLE_ENDIAN

#define MY_BIG_ENDIAN

#elif __BYTE_ORDER == __BIG_ENDIAN

#undef MY_BIG_ENDIAN

#endif

Determining the stack pointer
Inline assembly can be written to determine the stack pointer.

int get_stack(void ••StackPtr)

{

  •StackPtr = 0;

 #ifdef CMP_x86

  __asm__ __volatile__ ("movl %%esp, %0": "=m" (StackPtr) );

 #else

 #error No code for this architecture in __FILE__

 #endif

 return(0);

}

Implementing compare and swap
Here's an example of implementing compare and swap for the Intel architecture.

bool_t My_CompareAndSwap(IN int •ptr, IN int old, IN int new)

{



#ifdef CMP_x86

        unsigned char ret;



        /• Note that sete sets a 'byte' not the word •/



        __asm__ __volatile__ (

                "  lock\n"

                "  cmpxchgl %2,%1\n"

                "  sete %0\n"

                : "=q" (ret), "=m" (•ptr)

                : "r" (new), "m" (•ptr), "a" (old)

                : "memory");



        return ret;

#else

#error No code for this architecture in __FILE__

#endif



}

Tutorial Pages:
» A Practical Checklist, Tips, and Insight Drawn from Experience
» Get the Build System Working
» Decide on a Viable Operating Environment
» Architecture-Specific Changes
» Choose an IPC Mechanism
» Select the Threading Model
» File System, Usage Parameters, Stacks
» Memory Maps and Using Shared Memory Segments
» Signaling
» Configure Kernel Karameters
» Parser Tools like lex/yacc
» Globalization Issues
» Security Concerns
» Locating Installed Packages and Variable Data
» Testing
» There's a Port in Every Storm
» Resources

First published by IBM DeveloperWorks

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