Differences

This shows you the differences between two versions of the page.

--- wswan:guide:c_assembly [2024/02/17 10:55] – created asie
+++ wswan:guide:c_assembly [2025/12/31 12:59] (current) – asie
@@ Line 1: / Line 1: @@
 ====== Writing assembly ======
-For writing entire functions in ASM, as well as more complex projects, it can be preferable to write external assembly files.
+In the Wonderful toolchain, assembly files use the ''.s'' extension. They are compiled using the GNU assembler and the C preprocessor.
-In the Wonderful toolchain, these files use the ''.s'' extension and are compiled using the GNU assembler and the C preprocessor.
+===== Creating an assembly file =====
 It is recommended to start with a preamble similar to the following:
@@ Line 17: / Line 17: @@
   - Include the Wonderful toolchain's basic definitions. This provides some useful assembly defines and macros.
-  - Include the libws library's definitions. This library supports being included in an assembler, and provides hardware-related defines. You may wish to skip this line if targetting the WonderWitch.
+  - Include the libws library's definitions. This header file supports being included in an assembler context, and provides hardware-related defines - such as I/O port names and masks.
   - Tell the assembler to emit 16-bit code; this is useful as the GNU assembler supports all kinds of x86 code, including 32-bit and 64-bit.
-  - Tell the assembler to emit 80186 code; this unlocks some additional 80186-exclusive opcodes supported on the NEC V30MZ
+  - Tell the assembler to emit 80186 code; this unlocks some additional 80186-exclusive opcodes supported on the NEC V30MZ.
-  - Tell the assembler to emit Intel-syntax assembly; this is entirely optional, but the examples for external assembly files in this guide all make use of the Intel syntax, as opposed to the AT&T syntax used in inline assembly.
+  - Tell the assembler to emit Intel-syntax assembly; this is entirely optional, but the examples for external assembly files in this guide all make use of the Intel syntax, as opposed to the default AT&T syntax used in inline assembly.
+Note that to export a symbol (make it visible outside of the specific file, or translation unit), you need to use ''.global'', like so:
+<code C>
+        .global strlen
+strlen:
+</code>
+===== Useful macros =====
+Including ''wonderful.h'' provides some useful macros from ''ia16.h''.
+==== Portable calling convention ====
+The ''small'' and ''medium'' targets use different calling conventions (near vs. far functions by default). The following macros abstract these differences away:
+  * **IA16_CALL** - use this macro in place of the ''call'' instruction to call C-callable functions.
+  * **IA16_CALL_LOCAL** - use this macro in place of the ''call'' instruction when calling another function //in the same section//.
+  * **IA16_JMP** - use this macro in place of the ''jmp'' instruction to jump to C-callable functions.
+  * **IA16_RET** - use this macro in place of the ''ret'' instruction to return from a C-callable function.
+  * **IA16_CALL_STACK_OFFSET(x)** - for portability between code models, you can use this macro to get a stack offset with the function return address accounted for. For example, in a //near// code model, ''IA16_CALL_STACK_OFFSET(10)'' returns ''12'', but in a //far// code model, it returns ''14''.