Re: question about linker

On 26/11/2024 16:18, Bart wrote:

On 26/11/2024 18:35, Thiago Adams wrote:

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(I think I know the answer but I would like to learn more.)
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I am using C89 as "compiler backend intermediate language".
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I want a very simple output that could facilitate the construction of a simple C89 compiler focused on code generation.
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I am removing these features from the generated code.
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  - typedef
  - enum
  - preprocessor
  - const

 I don't use them in generated code either. (Only in a brief section at the top to define my prefered type designations.)

I am generating the prototypes for all functions called.
No includes, no macros.
The generated code is depending on compiler flags , platform and headers. It is intended to direct usage like in the pipeline
use my_compiler -> C89 -> CC

 

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At this output, I am generating the prototypes for the functions I call.
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For instance,
int strcmp( const char* lhs, const char* rhs );
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is generated as
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int strcmp( char* lhs, char* rhs );

 I don't use #include either, not even for standard headers, although gcc doesn't like it when I define my own std library functions. There are ways to shut it up though.
 

I am also generating the structs as required (on demand). For the structs I am renaming it because I am generating all structs at global scope.
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Question:
Does the compiler/linkers? Cares If I am lying about const? Or If rename the structs?
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I think it does not care, and it seems to work (it compiles and run).

 I don't know why the linker would care about anything. All it sees are symbol imports and exports.
 A compiler might care about lack of 'const' in that it could stop it doing doing some optimisations.
 But it can't report a type mismatch between 'const' and non-'const' types if 'const' has been banished completely.
 

I think GCC has some builtin functions and he can complain if the function prototype differs.
Do you have any idea what else can be simplified when creating a C compiler?
I was thinking about literal strings.
Instead of
f("abc");
Generating something like
char literal_string_1[] = {'a', 'b', 'c', '\0' }; //or numbers global
f(literal_string_1);
The reason I believe compilers already have to do this right? (put strings in a data section)
So this was one extra simplification I was thinking about.
Also remove  loops (for , while) and switches.
I was considering to remove sizeof but I think this will be part (together with structs and align) of any compiler even simpler ones.
When thinking about this, I consider the first version of C, K&R was already very complete in terms of code generation.
The evolution of C is much more about facilities like enuns, compound literals than something that is created to code generation.