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From: Amavect <amavect@gmail.com>
To: 9front@9front.org
Subject: Re: [9front] exec suicide: sys: bad address in syscall
Date: Sun, 8 May 2022 15:10:21 -0500	[thread overview]
Message-ID: <20220508151021.7cc0f0df@spruce.localdomain> (raw)
In-Reply-To: <CAO+DOcqq4RSa_vyhEHBxjGgmJ-ux_B3ShWMN-cy5YquWnaChtw@mail.gmail.com>

On Sun, 8 May 2022 17:38:27 +0000
istvan bak <bdhpfl@gmail.com> wrote:

> term% 6.red 666: suicide: invalid address 0x7fff00000000/1 in sys call

> 		execl("/bin/rc", "/bin/rc", "-c", cmd, 0);

You have been bitten by varargs.

The 4 bytes of 0x7fff00000000 is 32 bits.
That 0 is a 32-bit integer.
The 0 is not being converted due to varargs.
Casting to (char*) or (void*) fixes your issue.

See the warning when compiling this:
print("%p", 0);
warning: red.c:17 format mismatch p INT, arg 2
This is a problem in every C implementation.
Varargs suck.

For fun, the disassembly:
without casting (MOVL moves a 32 bit value):
rc+0x42 0x000000000020006a	MOVL	$0x0,0x20(SP)
rc+0x4a 0x0000000000200072	CALL	execl(SB)

with casting (MOVQ moves a 64 bit value):
rc+0x42 0x000000000020006a	MOVQ	$0x0,0x20(SP)
rc+0x4b 0x0000000000200073	CALL	execl(SB)

Note that run2() doesn't cast, either.
You got lucky that the higher 32 bits are zero.


  parent reply	other threads:[~2022-05-08 20:14 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-08 17:38 istvan bak
2022-05-08 19:53 ` ori
2022-05-08 20:10 ` Amavect [this message]
2022-05-08 21:45   ` istvan bak

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