[mono][aot] Improve toolchain configuration in Mono AOT compiler

[kotlarmilos]

The Mono AOT compiler comes with a predefined set of toolchain configurations for particular platforms.

runtime/src/mono/mono/mini/aot-compiler.c

Lines 13202 to 13216 in ffa4ef7

	#ifdef TARGET_WIN32_MSVC
	#define AS_OPTIONS "--target=x86_64-pc-windows-msvc -c -x assembler"
	#elif defined(TARGET_AMD64) && !defined(TARGET_MACH)
	#define AS_OPTIONS "--64"
	#elif defined(TARGET_POWERPC64)
	#define AS_OPTIONS "-a64 -mppc64"
	#elif defined(TARGET_X86) && defined(TARGET_MACH)
	#define AS_OPTIONS "-arch i386"
	#elif defined(TARGET_X86) && !defined(TARGET_MACH)
	#define AS_OPTIONS "--32"
	#elif defined(MONO_ARCH_ENABLE_PTRAUTH)
	#define AS_OPTIONS "-arch arm64e"
	#else
	#define AS_OPTIONS ""
	#endif

The current implementation does not allow for full extensibility in cases when the default toolchain is not available. To mitigate this, the #92057 introduces the as_name and as_options, along with ld_name and ld_options to allow specific toolchain configuration.

However, there are cases where the default properties are combined with parameters. For example, even though the ld-name is passed as an argument, if the LD_NAME is not defined, the default configuration is used:

runtime/src/mono/mono/mini/aot-compiler.c

Lines 13351 to 13375 in ffa4ef7

	#if defined(LD_NAME)
	if (ld_binary_name == NULL) {
	ld_binary_name = LD_NAME;
	}
	if (acfg->aot_opts.tool_prefix)
	g_string_append_printf (str, "\"%s%s\" %s", tool_prefix, ld_binary_name, LD_OPTIONS);
	else if (acfg->aot_opts.llvm_only)
	g_string_append_printf (str, "%s", acfg->aot_opts.clangxx);
	else
	g_string_append_printf (str, "\"%s%s\" %s", tool_prefix, ld_binary_name, LD_OPTIONS);
	#else
	if (ld_binary_name == NULL) {
	ld_binary_name = "ld";
	}
	// Default (linux)
	if (acfg->aot_opts.tool_prefix)
	/* Cross compiling */
	g_string_append_printf (str, "\"%s%s\" %s", tool_prefix, ld_binary_name, LD_OPTIONS);
	else if (acfg->aot_opts.llvm_only)
	g_string_append_printf (str, "%s", acfg->aot_opts.clangxx);
	else
	g_string_append_printf (str, "\"%s%s\"", tool_prefix, ld_binary_name);
	g_string_append_printf (str, " -shared");
	#endif

In order to enable easier code maintenance and to improve flexibility in utilizing different toolchains, the proposal is to introduce the PlatformConfig struct:

typedef struct {
    const char* as_name;
    const char* as_options;
    const char* as_object_file_suffix;
    const char* ld_name;
    const char* ld_options;
} PlatformConfig;

It can be defined as follows:

void compile_asm(MonoAotCompile* acfg, const CompileConfig* config)

And utilized as below:

compile_asm(acfg, &CONFIG_WIN32_MSVC);
// or
compile_asm(acfg, &CONFIG_LINUX);

The structs may be defined in a separate configuration file that is linked with the AOT compiler. This approach would enable the creation of default configurations according to the host OS and architecture in a structured manner and allow parameterizing these options.

/cc: @vargaz @lambdageek

[vargaz]

We have an utils/options-def.h file with some support for options which are compile time constants, perhaps this stuff can be added there ?

[kotlarmilos]

Lower priority compared to other tasks.