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Indirect branch and function attributes

Lorenzo Niceforo

Hi to everyone,

i am trying to use pointer functions to do indirect branch in C code, i am working with an NXP ARM LPC2478

This is my code:

// in internal flash
unsigned char* MD5BuffSE(unsigned char *pBuffer, unsigned long lOffset, unsigned long lSize)
{
   ...
}

g_CriptAddress.pMd5 = (void*)&MD5BuffSE; // g_CriptAddress is an array of void*


.....

// in internal ram @ 0x4000fd00
typedef unsigned char* (*MD5)(unsigned char* , unsigned long , unsigned long );
MD5 Md5 = (MD5)g_CriptAddress.pMd5;

if(memcmp(Md5((byte*)TOS_START, 0, TOS_DIM),pDataProt->ChkSumMd5,16)!=0)
        return false;

with this code all seems to works fine (code jumps to the right address and returns well), but next branch causes execution to fail with an abort exception.

if i use MD5BuffSE directly all works, but i noticed that compiler insert a long ARM to ARM veneer

so i ask myself if exist a way to tell compiler that it has to consider typedef MD5 a far call or to force it to create a long ARM to AMR veneer

what happens when i call a thumb function from arm code with indirect branch?

Lorenzo

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