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Date: Sun, 21 Nov 2004 17:10:59 -0500 (EST)
From: linux-os <linux-os@chaos.analogic.com>
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To: Russell King <rmk+lkml@arm.linux.org.uk>
cc: Linus Torvalds <torvalds@osdl.org>,
       Linux Kernel List <linux-kernel@vger.kernel.org>
Subject: Re: sparse segfaults
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On Sat, 20 Nov 2004, Russell King wrote:

> Linus,
>
> Sparse appears to segfault when trying to check kernel/timer.c:
>
>  CC      kernel/ptrace.o
>  CHECK   /home/rmk/bk/linux-2.6-rmk/kernel/timer.c
> make[2]: *** [kernel/timer.o] Error 139
> make[1]: *** [kernel] Error 2
> make: *** [_all] Error 2
>
> It doesn't seem to matter which ARM machine I have my kernel configured
> for, the result is always the same.
>
> #0  0x08059222 in expand_conditional (expr=0xf6a88c4c) at expand.c:478
> 478                     *expr = *true;
> (gdb) where
> #0  0x08059222 in expand_conditional (expr=0xf6a88c4c) at expand.c:478
> #1  0x08059956 in expand_expression (expr=0xf6a88c4c) at expand.c:859
> #2  0x08059a32 in expand_symbol (sym=0x5) at expand.c:917
> #3  0x08048cc0 in clean_up_symbols (list=0x9464fb0) at check.c:100
> #4  0x08048eb5 in main (argc=40, argv=0xfef19dc4) at check.c:192
> (gdb) print expr
> $1 = (struct expression *) 0xf6a88c4c
> (gdb) print true
> $2 = (struct expression *) 0x0
> (gdb) print *expr
> $3 = {type = EXPR_CONDITIONAL, op = 63, pos = {type = 6, stream = 1,
>    newline = 0, whitespace = 1, pos = 22, line = 566, noexpand = 0},
>  ctype = 0x80764a0, {value = 4138241036, fvalue = <invalid float value>,
>    string = 0xf6a88c0c, unop = 0xf6a88c0c, statement = 0xf6a88c0c,
>    expr_list = 0xf6a88c0c}}
>
> Unfortunately, gdb won't show me the contents of expr->cond_true nor
> expr->cond_false without the following:
>
> (gdb) print *(&expr->string)
> $4 = (struct string *) 0xf6a88c0c
> (gdb) print *(&expr->string+1)
> $5 = (struct string *) 0x0
> (gdb) print *(&expr->string+2)
> $6 = (struct string *) 0xf6a88c6c
>
> Looks like expr->cond_true is NULL.  Line 566 of kernel/timer.c is:
>
> int tickadj = 500/HZ ? : 1;             /* microsecs */
>
> which makes it look like sparse doesn't understand such constructions.

I don't think any 'C' compiler should understand such constructions
either.
 	There is no result for the TRUE condition, and the standard
does not provide for a default. The compiler should have written
a diagnostic.


>
> -- 
> Russell King
> Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
> maintainer of:  2.6 PCMCIA      - http://pcmcia.arm.linux.org.uk/
>                 2.6 Serial core


Cheers,
Dick Johnson
Penguin : Linux version 2.6.9 on an i686 machine (5537.79 BogoMips).
  Notice : All mail here is now cached for review by John Ashcroft.
                  98.36% of all statistics are fiction.
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