Add APE support for 32-bit programs

This is an experimental proof of concept demo:

    make -j8 o//examples/i386.i386.com
    o//examples/i386.i386.com --32
    echo $?  # <-- prints main32's argc parameter

Please note there's no libc support at the moment. This change is just
for fun and shouldn't be interpreted as intent to support. Having this
project on the whole support i386 would be tough because the calling
conventions are so different. There really isn't much in the way of low
hanging fruit opportunities to do something like NOP out REX prefixes
and call it a day. It'd likely need disjoint builds or possibly better
yet really cleverly crafted code generation in //third_party/chibicc!

Another challenge is is that Linux changed its SYSCALL ordinals when it
migrated from i386 to x86_64. Linux used to use the same magic numbers
as everyone else for functions like exit/write/read/etc. BSDs on the
other hand didn't pointlessly renumber things. So we'd need to find a
way to define the ordinals in libc/sysv/syscalls.sh twice for Linux. The
same goes for other ISAs too. Especially MIPS. For the Linux Kernel
alone, syscall magic numbers and data structure layouts are totally
different, and that's likely the case for other ISAs on other operating
systems too. Probably because ISA code historically got contributed to
open source by the companies that made the chips. Ulrich Drepper wrote
an amusing essay on the subject some years back.

ape/ape.S

@@ -487,6 +487,36 @@ apesh:	.ascii	"'\n#'\"\n"			# sixth edition shebang
 	.ascii	"el"
 #endif
 	.ascii	"if exec 7<> \"$o\"; then\n"
+
+//	Writes 32-bit ELF header if --32 is the first argument
+//	This should be changed to check $(uname -m) on ENOEXEC
+	.ascii	  "if [ x\"$1\" = x--32 ]; then\n"
+	.ascii	  "printf '"
+	.ascii	    "\\177ELF"			# 0x0: ⌂ELF
+	.ascii	    "\\1"			#   4: legacy mode
+	.ascii	    "\\1"			#   5: little endian
+	.ascii	    "\\1"			#   6: elf v1.o
+	.ascii	    "\\011"			#   7: FreeBSD
+	.ascii	    "\\0"			#   8: os/abi ver.
+	.ascii	    "\\0\\0\\0"			#   9: padding 3/7
+	.ascii	    "\\0\\0\\0\\0"		#      padding 4/7
+	.ascii	    "\\2\\0"			#  10: εxεcµταblε
+	.ascii	    "\\3\\0"			#  12: i386
+	.ascii	    "\\1\\0\\0\\0"		#  14: elf v1.o
+	.shstub	    ape_elf32_entry,4		#  18: e_entry
+	.shstub	    ape_elf32_phoff,4		#  1c: e_phoff
+	.shstub	    ape_elf32_shoff,4		#  20: e_shoff
+	.ascii	    "\\0\\0\\0\\0"		#  24: e_flags
+	.ascii	    "\\100\\0"			#  28: e_ehsize
+	.ascii	    "\\040\\0"			#  2a: e_phentsize
+	.shstub	    ape_elf32_phnum,2		#  2c: e_phnum
+	.ascii	    "\\0\\0"			#  2e: e_shentsize
+	.shstub	    ape_elf32_shnum,2		#  30: e_shnum
+	.shstub	    ape_elf32_shstrndx,2	#  32: e_shstrndx
+	.ascii	    "' >&7\n"
+	.ascii	  "else\n"
+
+//	Standard 64-bit ELF Header
 	.ascii	  "printf '"
 	.ascii	    "\\177ELF"			# 0x0: ⌂ELF
 	.ascii	    "\\2"			#   4: long mode
@@ -510,6 +540,8 @@ apesh:	.ascii	"'\n#'\"\n"			# sixth edition shebang
 	.shstub	    ape_elf_shnum,2		#  3c: e_shnum
 	.shstub	    ape_elf_shstrndx,2		#  3e: e_shstrndx
 	.ascii	    "' >&7\n"
+	.ascii	  "fi\n"
+
 	.ascii	  "exec 7<&-\n"
 	.ascii	"fi\n"
 	.ascii	"exec \"$0\" \"$@\"\n"		# etxtbsy tail recursion

ape/ape.lds

@@ -207,6 +207,9 @@ SECTIONS {
     HIDDEN(ape_phdrs = .);
     KEEP(*(.elf.phdrs))
     HIDDEN(ape_phdrs_end = .);
+    HIDDEN(ape_phdrs32 = .);
+    KEEP(*(.elf.phdrs32))
+    HIDDEN(ape_phdrs32_end = .);
 
     /* OpenBSD */
     . = ALIGN(__SIZEOF_POINTER__);
@@ -246,7 +249,7 @@ SECTIONS {
 /*END: realmode addressability guarantee */
 
     /* Normal Code */
-    *(.start)
+    KEEP(*(.start))
     KEEP(*(.initprologue))
     KEEP(*(SORT_BY_NAME(.init.*)))
     KEEP(*(.init))
@@ -445,6 +448,13 @@ PFSTUB4(ape_elf_phnum, (ape_phdrs_end - ape_phdrs) / 56);
 PFSTUB4(ape_elf_shnum, 0);
 PFSTUB4(ape_elf_shstrndx, 0);
 
+PFSTUB4(ape_elf32_entry, _start32);
+PFSTUB4(ape_elf32_phoff, RVA(ape_phdrs32));
+PFSTUB4(ape_elf32_shoff, 0);
+PFSTUB4(ape_elf32_phnum, (ape_phdrs32_end - ape_phdrs32) / 32);
+PFSTUB4(ape_elf32_shnum, 0);
+PFSTUB4(ape_elf32_shstrndx, 0);
+
 HIDDEN(__privileged_addr = ROUNDDOWN(__privileged_start, PAGESIZE)); 
 HIDDEN(__privileged_size = (ROUNDUP(__privileged_end, PAGESIZE) -
                             ROUNDDOWN(__privileged_start, PAGESIZE))); 

build/definitions.mk

@@ -299,6 +299,11 @@ OBJECTIFY.greg.c =							\
 	-fno-sanitize=all						\
 	-c
 
+OBJECTIFY.i386.c =							\
+	$(OBJECTIFY.c)							\
+	-m32								\
+	-wrapper build/i386ify.sh
+
 OBJECTIFY.ansi.c = $(CC) $(OBJECTIFY.c.flags) -ansi -Wextra -Werror -pedantic-errors -c
 OBJECTIFY.c99.c = $(CC) $(OBJECTIFY.c.flags) -std=c99 -Wextra -Werror -pedantic-errors -c
 OBJECTIFY.c11.c = $(CC) $(OBJECTIFY.c.flags) -std=c11 -Wextra -Werror -pedantic-errors -c

build/i386ify.sh

@@ -0,0 +1,35 @@
+#!/bin/sh
+#
+# SYNOPSIS
+#
+#   gcc -m32 -wrapper build/i386ify.sh -c -o foo.o foo.c
+#
+# OVERVIEW
+#
+#   Compiles 32-bit code inside 64-bit ELF objects.
+
+if [ "${1##*/}" = as ]; then
+  FIRST=0
+  for x; do
+    if [ $FIRST -eq 0 ]; then
+      set --
+      FIRST=1
+    fi
+    if [ "$x" = "--32" ]; then
+      continue
+    fi
+    if [ "${x##*.}" = s ]; then
+      {
+        printf "\t.section .yoink\n"
+        printf "\tnopl\t_start32\n"
+        printf "\t.previous\n"
+        printf "\t.code32\n"
+        cat "$x"
+      } >"$x".tmp
+      mv -f "$x".tmp "$x"
+    fi
+    set -- "$@" "$x"
+  done
+fi
+
+exec "$@"

build/rules.mk

@@ -64,6 +64,7 @@ o/$(MODE)/%.lds: %.lds             ; @$(COMPILE) -APREPROCESS $(PREPROCESS.lds)
 o/$(MODE)/%.h.ok: %.h              ; @$(COMPILE) -ACHECK.h $(COMPILE.c) -x c -g0 -o $@ $<
 o/$(MODE)/%.h.okk: %.h             ; @$(COMPILE) -ACHECK.h $(COMPILE.cxx) -x c++ -g0 -o $@ $<
 o/$(MODE)/%.o: %.greg.c            ; @$(COMPILE) -AOBJECTIFY.greg $(OBJECTIFY.greg.c) $(OUTPUT_OPTION) $<
+o/$(MODE)/%.i386.o: %.i386.c       ; @$(COMPILE) -AOBJECTIFY.i386 $(OBJECTIFY.i386.c) $(OUTPUT_OPTION) $<
 o/$(MODE)/%.greg.o: %.greg.c       ; @$(COMPILE) -AOBJECTIFY.greg $(OBJECTIFY.greg.c) $(OUTPUT_OPTION) $<
 o/$(MODE)/%.ansi.o: %.ansi.c       ; @$(COMPILE) -AOBJECTIFY.ansi $(OBJECTIFY.ansi.c) $(OUTPUT_OPTION) $<
 o/$(MODE)/%.ansi.o: %.c            ; @$(COMPILE) -AOBJECTIFY.ansi $(OBJECTIFY.ansi.c) $(OUTPUT_OPTION) $<

examples/i386.i386.c

@@ -0,0 +1,19 @@
+#if 0
+/*─────────────────────────────────────────────────────────────────╗
+│ To the extent possible under law, Justine Tunney has waived      │
+│ all copyright and related or neighboring rights to this file,    │
+│ as it is written in the following disclaimers:                   │
+│   • http://unlicense.org/                                        │
+│   • http://creativecommons.org/publicdomain/zero/1.0/            │
+╚─────────────────────────────────────────────────────────────────*/
+#endif
+#include "libc/str/str.h"
+
+char kTenFour[10] = {4, 4, 4, 4, 4, 4, 4, 4, 4, 4};
+
+int main32(int argc, char *argv[]) {
+  return argc;
+  if (memset(argv[0], 4, 10) != argv[0]) return 1;
+  if (memcmp(argv[0], kTenFour, 10)) return 2;
+  return 0;
+}

libc/elf/iself64binary.c

@@ -23,5 +23,6 @@ bool IsElf64Binary(const Elf64_Ehdr *elf, size_t mapsize) {
   if (mapsize < sizeof(Elf64_Ehdr)) return false;
   if (memcmp(elf->e_ident, ELFMAG, 4)) return false;
   return (elf->e_ident[EI_CLASS] == ELFCLASSNONE ||
-          elf->e_ident[EI_CLASS] == ELFCLASS64);
+          elf->e_ident[EI_CLASS] == ELFCLASS64 ||
+          elf->e_ident[EI_CLASS] == ELFCLASS32);
 }

libc/nexgen32e/bsrmax.S

@@ -33,6 +33,7 @@
 //	@param	rsi:rdi is 128-bit unsigned 𝑥 value
 //	@return	eax number in range [0,128) or undef if 𝑥 is 0
 //	@see	also treasure trove of nearly identical functions
+//	@mode	legacy,long
 bsrmax:	.leafprologue
 	.profilable
 	bsr	%rsi,%rax

libc/runtime/crt32.S

@@ -0,0 +1,84 @@
+/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8     -*-│
+│vi: set et ft=asm ts=8 tw=8 fenc=utf-8                                     :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2021 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "ape/macros.internal.h"
+#include "libc/dce.h"
+#include "libc/elf/def.h"
+#include "libc/macros.h"
+.section .start,"ax",@progbits
+.code32
+
+//	@fileoverview 80386 APE UNIX CRT
+//
+//	This module is yoinked by build/i386ify.sh when GNU make
+//	builds source codes that have the .i386.c file extension
+//	thereby avoiding some 386 bloat when it isn't being used
+//
+//	TODO: Verify we can't use 64-bit ELF with i386 e_machine
+
+_start32:
+	.weak	main32
+	call	main32
+	mov	%eax,%ebx
+	pushpop	1,%eax				# _exit() ordinal
+	push	%ebx				# hybrid calling convention
+	push	%eax				# should work on Linux+BSDs
+	int	$0x80
+	ud2
+	.endfn	_start32,globl,hidden
+
+	.section .elf.phdrs32,"a",@progbits
+	.long	PT_LOAD				# text segment
+	.stub	ape_rom_offset,long
+	.stub	ape_rom_vaddr,long
+	.stub	ape_rom_paddr,long
+	.stub	ape_rom_filesz,long
+	.stub	ape_rom_memsz,long
+	.long	PF_R|PF_X			# <-- wut
+	.stub	ape_rom_align,long
+	.long	PT_LOAD				# data segment
+	.stub	ape_ram_offset,long
+	.stub	ape_ram_vaddr,long
+	.stub	ape_ram_paddr,long
+	.stub	ape_ram_filesz,long
+	.stub	ape_ram_memsz,long
+	.long	PF_R|PF_W
+	.stub	ape_ram_align,long
+#if SupportsLinux()
+//	Linux ignores mprotect() and returns 0 without this lool
+//	It has nothing to do with the stack, which is still exec
+	.long	PT_GNU_STACK			# p_type
+	.long	0				# p_offset
+	.long	0				# p_vaddr
+	.long	0				# p_paddr
+	.long	0				# p_filesz
+	.long	0				# p_memsz
+	.long	PF_R|PF_W			# p_flags
+	.long	16				# p_align
+#endif
+#if SupportsOpenbsd() || SupportsNetbsd()
+	.long	PT_NOTE				# notes
+	.stub	ape_note_offset,long
+	.stub	ape_note_vaddr,long
+	.stub	ape_note_paddr,long
+	.stub	ape_note_filesz,long
+	.stub	ape_note_memsz,long
+	.long	PF_R
+	.stub	ape_note_align,long
+#endif
+	.previous