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Initial commit of echo
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‎LICENSE

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Copyright (c) 2020 Brian Callahan <[email protected]>
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Permission to use, copy, modify, and distribute this software for any
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purpose with or without fee is hereby granted, provided that the above
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copyright notice and this permission notice appear in all copies.
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THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

‎Makefile

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# echo Makefile
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CC = cc
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CFLAGS = -Oz -nostdinc -fomit-frame-pointer
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CFLAGS += -fno-PIE -fno-PIC -fno-ret-protector
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CFLAGS += -fno-stack-protector -mno-retpoline
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CFLAGS += -fno-asynchronous-unwind-tables
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CFLAGS += -Wno-int-to-void-pointer-cast
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PROG = echo
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OBJS = _start.o _syscall.o crt.o echo.o
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all: ${OBJS}
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/usr/bin/ld -nopie -o ${PROG} ${OBJS}
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/usr/bin/strip ${PROG}
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/usr/bin/strip -R .comment ${PROG}
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clean:
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rm -rf ${PROG} ${OBJS} ${PROG}.core ${PROG}~

‎README.md

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echo
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====
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echo is a reimplementation of the echo(1) utility without libc.
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It is used to teach how argc and argv are passed in Unix.
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Why?
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----
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Read my
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[blog post](https://briancallahan.net/blog/20200808.html)
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about this codebase.
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Building
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--------
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Just run `make`.
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This will probably only run on
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[OpenBSD](https://www.openbsd.org)/amd64
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as is.
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Feel free to port to your Unix of choice.
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License
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-------
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ISC License.
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See `LICENSE` for details.

‎_start.s

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/*
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* Copyright (c) 2020 Brian Callahan <[email protected]>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* 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 WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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.text
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.p2align 2
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.globl _start
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_start:
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popq %rdi
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movq %rsp, %rsi
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movq 8(%rsp, %rdi, 8), %rdx
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callq main
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movl %eax, %edi
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movl $1, %eax
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syscall
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.size _start,.-_start

‎_syscall.s

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/*
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* Copyright (c) 2020 Brian Callahan <[email protected]>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* 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 WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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.text
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.p2align 2
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.globl _syscall
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_syscall:
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movq %rdi, %rax
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movq %rsi, %rdi
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movq %rdx, %rsi
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movq %rcx, %rdx
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movq %r8, %rcx
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movq %r9, %r8
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syscall
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retq
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.size _syscall,.-_syscall

‎crt.s

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/*
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* Copyright (c) 2020 Brian Callahan <[email protected]>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* 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 WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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.section ".note.openbsd.ident", "a"
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.p2align 2
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.long 0x8
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.long 0x4
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.long 0x1
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.asciz "OpenBSD"
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.long 0x0
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.previous

‎echo.c

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/*
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* Copyright (c) 2020 Brian Callahan <[email protected]>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* 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 WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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/*
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* echo -- print out argv
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*/
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extern void *_syscall(void *n, void *a, void *b, void *c, void *d, void *e);
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static void
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write(int d, const void *buf, unsigned long nbytes)
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{
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_syscall((void *) 4, (void *) d, (void *) buf, (void *) nbytes, (void *) 0, (void *) 0);
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}
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static unsigned long
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strlen(const char *s)
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{
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char *t;
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t = (char *) s;
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while (*t != '\0')
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t++;
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return t - s;
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}
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int
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main(int argc, char *argv[])
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{
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int i;
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for (i = 1; i < argc; i++) {
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write(1, argv[i], strlen(argv[i]));
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if (i + 1 != argc)
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write(1, " ", 1);
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}
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write(1, "\n", 1);
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return 0;
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}

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