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--- wswan:guide:c_assembly [2024/02/17 10:55] – created asie
+++ wswan:guide:c_assembly [2024/03/16 13:01] (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 library supports being included in an assembler, 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 =====
+''wonderful.h'' provides some useful macros:
+  * **WF_PLATFORM_CALL** - for portability between code models, you can use this macro in place of the ''call'' instruction to call C functions.
+  * **WF_PLATFORM_JMP** - for portability between code models, you can use this macro in place of the ''jmp'' instruction to jump to C functions.
+  * **WF_PLATFORM_RET** - for portability between code models, you can use this macro in place of the ''ret'' isntruction to return from a C-called function.
+  * **WF_PLATFORM_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 exapmle, in a "near" code model, ''WF_PLATFORM_CALL_STACK_OFFSET(10)'' returns ''12'', but in a "far" code model, it returns ''14''.