Zilog EZ80F916 - Manual (Page 172)

UM014423-0607 Using the ANSI C-Compiler
ZiLOG Developer Studio II
eZ80Acclaim! ® User Manual
152
•
Returning structure
If the function returns a structure, the caller allocates the space for the structure and
then passes the address of the return space to the called function as an additional and
first argument. To return a structure, the called function then copies the structure to the
memory block pointed to by this argument.
•
Not allocating a local frame
The compiler does not allocate a local stack frame for a function in the following case:
–
The function does not have any local stack variables, stack arguments, or
compiler-generated temporaries on the stack.
and
–
The function does not return a structure.
and
–
The function is compiled without the debug option.
CALLING ASSEMBLY FUNCTIONS FROM C
The eZ80Acclaim! C-Compiler allows mixed C and assembly programming. A function
written in assembly can be called from C if the assembly function follows the C calling
conventions as described in “Calling Conventions” on page 149.
The following sections describe how to call assembly functions from C:
•
“Function Naming Convention” on page 152
•
“Variable Naming Convention” on page 152
•
“Argument Locations” on page 153
•
“Return Values” on page 153
•
“Preserving Registers” on page 153
Function Naming Convention
Assembly function names must be preceded with an _ (underscore) in order to be callable
from C. The compiler prefixes C function names with an underscore in the generated
assembly. For example, a call to
myfunc() in C is translated to a call to _myfunc in gen-
erated assembly by the compiler.
Variable Naming Convention
When the compiler generates an assembly file from C code, all names of global variables
are prefixed with an underscore.
Names of local static variables are prefixed with an underscore followed by a function
number to avoid assembly errors when the same local static variable occurs more than
once in the same file.