Problem with mixing C and assembly codes on CC5.4 and Tiva launchpad

The construct 'extern "C"' is a C++ construct, and is illegal syntax in C code.  Rename your file to main.cpp or use the --cpp_default (also known as -fg) option to tell the compiler that .c files are actually C++ files.

Thanks Archaelogist for reply and I am sorry for my delay.

I did what you suggested (-fg option for main_cpp.c)

but I received following errors

In line 9 I got syntax error, and finally in the Problems window I got

Well, I looked for the other way of mixing asm and C, and I applied different structure:

in main.c

extern int asmfunc(int a); /* declare external asm function */

int gvar = 0; /* define global variable */

int main(void) {

     int i=5;

    i = asmfunc(i);

    while(1) {} 

 } 

 in asm_file.s

      .def asmfunc

      .ref gvar

asmfunc:

      LDR r1, gvar_a

      LDR r2, [r1, #0]

      ADD r0, r0, r2

      STR r0, [r1, #0]

      MOV R0,#3

     MOV pc, lr

gvar_a .field gvar, 32

below is screenshot after building and debugging. It works! However I it is interesting why previous example doesn't work.  

Your assembly file is different; the version that works does not have a leading underscore on the name asmfunc.  In EABI mode, you should not use a leading underscore.

Ok. That works correctly. As you suggested I changed asm code:

.global asmfunc

.global gvar

asmfunc:

     LDR r1, gvar_a

     LDR r2, [r1, #0]

     ADD r0, r0, r2

     STR r0, [r1, #0]

     MOV pc, lr

gvar_a .field gvar, 32

It seems to me, there is a problem in SPRU151 exapmle 6-1 and 6-2. The code is not EABI standard and might encumber understanding of the issue. I suggest correcting the document.

Thanks in advance for your support.