Is there a way to inline the main function?

[micycle8778]

I am trying to setup my own target via the porting guide on the wiki, and I was wondering if there was a way to inline the main function. My _start currently just contains a jsr to my main function, and I'd like to get rid of the overhead, especially because stack space is limited to one page.

[micycle8778]

We found a workaround that seems to work.

[nix-shell:~/Documents/6502]$ cat src/main.c --plain
void _irqbrk(void) {
}

__attribute__((section(".call_main")))
void _start(void) {
    // some random code to prove what we're writing here is
    // ending up in the binary
    *(volatile char*)(0x6000) = 0xD;
}

[nix-shell:~/Documents/6502]$ make objdump
mkdir -p out/
llvm-mos/bin/mos-clang -Os -Iinc -nostartfiles -Lllvm-mos/mos-platform/common/lib src/main.c -o out/rom.img
llvm-mos/bin/llvm-objdump -d out/rom.img.elf

out/rom.img.elf:	file format elf32-mos

Disassembly of section .text:

00008000 <_start>:
    8000: a2 0d        	ldx	#$d
    8002: 8e 00 60     	stx	$6000                   ; 0x6000 <__heap_start+0x5e00>
    8005: 60           	rts

00008006 <_irqbrk>:
    8006: 60           	rts

If you use the base mos-clang compiler and use -nostartfiles and link the common libc, you can get it to build. To include your main, you need to annotate it with __attribute__((section(".call_main"))), which is the section the linker uses to call your main, but we're abusing that section to just paste in our main.
The only problem is there's an rts that'll take you to who knows where at the end there, but if you end your main with an infinite loop, the compiler won't emit an rts.

I'm not sure if this is a "proper" way to do this, someone who knows the toolchain better might see some kind of footgun.