use _start, but don't call it ;)

Makefile

@@ -38,7 +38,7 @@ $(OBJDIR)/symbols.%.s: $(OBJDIR)/%.o.syms
 	$(LDRDIR)/mksyms $(LIBS) $$(cat $^) > $@
 
 $(OBJDIR)/header.%.o: $(OBJDIR)/symbols.%.s $(LDRDIR)/header.s $(LDRDIR)/loader.s
-	nasm $(ASFLAGS) $< -o $@
+	nasm -DUSE_INTERP $(ASFLAGS) $< -o $@
 
 $(BINDIR)/%: $(OBJDIR)/%.o $(OBJDIR)/header.%.o
 	$(LD) -m elf_i386 $(LDFLAGS) $^ -o $@

ldr/header.s

@@ -20,7 +20,7 @@ header:
         ; e_version
         dd 1
         ; e_entry
-        dd _start
+        dd _smol_start
         ; e_phoff
         dd (.segments - header)
         ; e_shoff

ldr/link.ld

@@ -6,7 +6,9 @@ SECTIONS {
   .header : { *(.header) }
 
   .text : {
-     *(.text .text.* .rdata .rdata.* .rodata .rodata.*)
+     *(.text._smol_start)
+     *(.text._start)
+     *(.text .rdata .rdata.* .rodata .rodata.*)
   }
 
   .data : {

ldr/loader.s

 ; vim: set ft=nasm ts=8:
-[section .text]
 
 %define LM_NAME_OFFSET           0x4
 %define LM_NEXT_OFFSET           0xC
@@ -22,6 +21,8 @@
 lm_off_extra:
     dd 0
 
+[section .text._smol_start]
+
 strcmp: ; (const char *s1 (esi), const char *s2 (edi))
        push esi
        push edi
@@ -130,15 +131,15 @@ link: ; (struct link_map *root, char *symtable)
 .done:  ret
 
 
-extern main
-_start:
+extern _start
+_smol_start:
         ; try to get the 'version-agnostic' pffset of the stuff we're
         ; interested in
         mov ebx, eax
         mov esi, eax
     .looper:
       lodsd
-        cmp dword eax, _start
+        cmp dword eax, _smol_start
         jne short .looper
         sub esi, ebx
         sub esi, LM_ENTRY_OFFSET_BASE+4 ; +4: take inc-after from lodsb into acct
@@ -150,6 +151,6 @@ _start:
        push eax
        call link
 
-       call main
-       int3
+        ;jmp short _start
+        ; by abusing the linker script, _start ends up right here :)
 

src/test.c

+#include <stdlib.h>
+#include <stdio.h>
+
+const char *f = "foo";
+
+__attribute__((__externally_visible__, __section__(".text._start"), __noreturn__))
+int _start(void) {
+    printf("hello world %s\n", f);
+    exit(42);
+    __builtin_unreachable();
+}