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POC Macro utilizing immediate values in embedded arm asm - armcc
 

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  1. POC Macro utilizing immediate values in embedded arm asm - armcc
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    <p>The closest threads to my question are these <a href="https://stackoverflow.com/questions/1135822/escaping-a-symbol-in-a-define-macro">Escaping a # symbol in a #define macro?</a> and <a href="https://stackoverflow.com/questions/1386597/how-to-print-a-pound-hash-via-c-preprocessor">How to print a pound / hash via C preprocessor?</a>, but they don't exactly answer my question. More explicitly, the second doesn't seem to work with the armcc compiler; it just prints hash4 and not the symbol defined by hash. Chris Lutz was especially disparaging of trying use a macro for this functionality in the second post, so maybe this is the incorrect method all together. I would like more thoughts than just one persons, though.</p> <p>The problem is the following: I'm trying to write a macro that defines an embedded asm C function utilizing a macro. I've essentially implemented it except for one issue... expressing an immediate value. Immediate values' syntax requires (I believe) a pound symbol which is also the "stringify" symbol for the preprocessor. So, is it possible to escape a # symbol in a C macro? </p> <p>The primary purpose behind this is to wrap an isr with a pico kernels thread context management procedures and that new procedure's function pointer will eventually be passed to the vectored interrupt controller.</p> <p>Here's the code:</p> <pre><code>#define ISR_THREAD_MGMT(ISR_FUNC,FUNC_NAME) \ __asm void FUNC_NAME ( void ); \ __asm void FUNC_NAME (void ) \ { \ STMDB sp!, {r0-r3}; \ MRS r0, SPSR; \ SUB lr, lr, #4; \ &lt;----- Heres the problem STMDB sp!, {r0, r10, r12, lr}; \ bl _thread_vectored_context_save; \ bl ISR_FUNC; \ b _thread_context_restore; \ } </code></pre> <p>I hope I've explained everything in sufficient detail. If not, please don't hesitate to ask for any more details.</p>
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    1. COMy first instinct was "don't use a macro for this", but clearly you've already seen someone else say that, so I'm not sure what you expect us to say - you are trying to use a macro pre-processor to do things it was never designed to do. If you were using at&t syntax, if would magically work because $ [indication of constant] is not a preprocessor "special character". One solution would of course be to actually write out FUNC_NAME and ISR_FUNC in individual functions - or not use the C compiler for assembler code...
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    2. COOverall, I was wanting a larger consensus than one person's thoughts. So, you are saying specifying embedded assembly instructions as a macro is outside its intended use? Weren't macros originally written to inline function calls? Furthermore, a text preprocessor that doesn't let you write all symbols? Seems strange to me...
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    3. COThe C preprocessor is intended for C - it's part of its name. When C was designed, inline assembler was not part of the scope - the compiler would produce assembler, and then assemble through the system assembler - if you wanted to add assembler code yourself, you wrote a `something.s` file - which is still a valid option. Most assemblers do have a macro functionality to let you produce the same code over and over with variations.
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