SPRUI03E June 2015 – January 2023
The .cdecls directive allows programmers in mixed assembly and C/C++ environments to share C headers containing declarations and prototypes between the C and assembly code. Any legal C/C++ can be used in a .cdecls block and the C/C++ declarations will cause suitable assembly to be generated automatically. This allows the programmer to reference the C/C++ constructs in assembly code — calling functions, allocating space, and accessing structure members — using the equivalent assembly mechanisms. While function and variable definitions are ignored, most common C/C++ elements are converted to assembly: enumerations, (non function-like) macros, function and variable prototypes, structures, and unions.
See the .cdecls directive description for details on the syntax of the .cdecls assembler directive.
The .cdecls directive can appear anywhere in an assembly source file, and can occur multiple times within a file. However, the C/C++ environment created by one .cdecls is not inherited by a later .cdecls; the C/C++ environment starts over for each .cdecls instance.
For example, the following code causes the warning to be issued:
.cdecls C,NOLIST
%{
#define ASMTEST 1
%}
.cdecls C,NOLIST
%{
#ifndef ASMTEST
#warn "ASMTEST not defined!" /* will be issued */
#endif
%}Therefore, a typical use of the .cdecls block is expected to be a single usage near the beginning of the assembly source file, in which all necessary C/C++ header files are included.
Use the compiler --include_path=path options to specify additional include file paths needed for the header files used in assembly, as you would when compiling C files.
Any C/C++ errors or warnings generated by the code of the .cdecls are emitted as they normally would for the C/C++ source code. C/C++ errors cause the directive to fail, and any resulting converted assembly is not included.
C/C++ constructs that cannot be converted, such as function-like macros or variable definitions, cause a comment to be output to the converted assembly file. For example:
; ASM HEADER WARNING - variable definition 'ABCD' ignoredThe prefix ASM HEADER WARNING appears at the beginning of each message. To see the warnings, either the WARN parameter needs to be specified so the messages are displayed on STDERR, or else the LIST parameter needs to be specified so the warnings appear in the listing file, if any.
Finally, note that the converted assembly code does not appear in the same order as the original C/C++ source code and C/C++ constructs may be simplified to a normalized form during the conversion process, but this should not affect their final usage.