FreeCalypso > hg > freecalypso-tools
view target-utils/libc/bzero.S @ 465:003e48f8ebe1
rvinterf/etmsync/fsnew.c: cast 0 to (char *) for execl sentinel
I generally don't use NULL and use plain 0 instead, based on a "NULL
considered harmful" discussion on the classiccmp mailing list many aeons
ago (I couldn't find it, and I reason that it must have been 2005 or
earlier), but a recent complaint by a packager sent me searching, and I
found this:
https://ewontfix.com/11/
While I don't give a @#$% about "modern" systems and code-nazi tools,
I realized that passing a plain 0 as a pointer sentinel in execl is wrong
because it will break on systems where pointers are longer than the plain
int type. Again, I don't give a @#$% about the abomination of x86_64 and
the like, but if anyone ever manages to port my code to something like a
PDP-11 (16-bit int, 32-bit long and pointers), then passing a plain 0
as a function argument where a pointer is expected most definitely won't
work: if the most natural stack slot and SP alignment unit is 16 bits,
fitting an int, with longs and pointers taking up two such slots, then
the call stack will be totally wrong with a plain 0 passed for a pointer.
Casting the 0 to (char *) ought to be the most kosher solution for the
most retro systems possible.
| author | Mychaela Falconia <falcon@freecalypso.org> |
|---|---|
| date | Mon, 11 Feb 2019 00:00:19 +0000 |
| parents | bfed7a5c21a6 |
| children |
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/* * This ARM implementation of bzero() has been derived from: * * linux/arch/arm/lib/memzero.S * * Copyright (C) 1995-2000 Russell King * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. */ .text .code 32 .globl bzero /* * Align the pointer in r0. r3 contains the number of bytes that we are * mis-aligned by, and r1 is the number of bytes. If r1 < 4, then we * don't bother; we use byte stores instead. */ 1: subs r1, r1, #4 @ 1 do we have enough blt 5f @ 1 bytes to align with? cmp r3, #2 @ 1 strltb r2, [r0], #1 @ 1 strleb r2, [r0], #1 @ 1 strb r2, [r0], #1 @ 1 add r1, r1, r3 @ 1 (r1 = r1 - (4 - r3)) /* * The pointer is now aligned and the length is adjusted. Try doing the * bzero again. */ bzero: mov r2, #0 @ 1 ands r3, r0, #3 @ 1 unaligned? bne 1b @ 1 /* * r3 = 0, and we know that the pointer in r0 is aligned to a word boundary. */ 3: subs r1, r1, #4 strcs r2, [r0], #4 bhi 3b @ 1 bxeq lr @ 1/2 quick exit /* * No need to correct the count; we're only testing bits from now on * * When we get here, we've got less than 4 bytes to zero. We * may have an unaligned pointer as well. */ 5: tst r1, #2 @ 1 2 bytes or more? strneb r2, [r0], #1 @ 1 strneb r2, [r0], #1 @ 1 tst r1, #1 @ 1 a byte left over strneb r2, [r0], #1 @ 1 bx lr @ 1