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face6b61d5
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.
46 lines
2.8 KiB
ArmAsm
46 lines
2.8 KiB
ArmAsm
/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8 -*-│
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│vi: set et ft=asm ts=8 tw=8 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2020 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/macros.h"
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// Returns binary logarithm of integer 𝑥.
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//
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// uint32 𝑥 bsf(𝑥) tzcnt(𝑥) ffs(𝑥) bsr(𝑥) lzcnt(𝑥)
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// 0x00000000 wut 32 0 wut 32
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// 0x00000001 0 0 1 0 31
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// 0x80000001 0 0 1 31 0
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// 0x80000000 31 31 32 31 0
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// 0x00000010 4 4 5 4 27
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// 0x08000010 4 4 5 27 4
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// 0x08000000 27 27 28 27 4
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// 0xffffffff 0 0 1 31 0
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//
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// @param rsi:rdi is 128-bit unsigned 𝑥 value
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// @return eax number in range [0,128) or undef if 𝑥 is 0
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// @see also treasure trove of nearly identical functions
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// @mode legacy,long
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bsrmax: .leafprologue
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.profilable
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bsr %rsi,%rax
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jnz 2f
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bsr %rdi,%rax
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1: .leafepilogue
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2: add $64,%eax
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jmp 1b
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.endfn bsrmax,globl
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.source __FILE__
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