Re: [PATCH 1/2] Enable a way to provide the reason for "being here"

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

On Wed, Jun 20, 2012 at 09:09:53PM +0200, Juergen Beisert wrote:
> Hi Uwe,
> 
> Uwe Kleine-König wrote:
> > On Wed, Jun 20, 2012 at 05:08:52PM +0200, Juergen Beisert wrote:
> > > Marc Kleine-Budde wrote:
> > > > [...]
> > > >
> > > > > +
> > > > > +#include <common.h>
> > > > > +#include <init.h>
> > > > > +#include <environment.h>
> > > > > +#include <globalvar.h>
> > > > > +#include <reset_source.h>
> > > > > +
> > > > > +static const char name[] = "global.system.reset";
> > > > > +static const char unknown_reset[] = "unknown";
> > > > > +static const char power_on_reset[] = "POR";
> > > > > +static const char manual_reset[] = "RST";
> > > > > +static const char watchdog[] = "WDG";
> > > > > +static const char wake[] = "WKE";
> > > > > +static const char jtag[] = "JTAG";
> > > >
> > > > what about using an array
> > > >
> > > > static cost char *reset_reason_array[] = {
> > > > 	[RESET_UKWN] = "unknown",
> > > > 	...
> > > > };
> > >
> > > The result is not the same. The strings are no longer "const". But it
> > > should
> >
> > <kidding>Of course they are not "const" if you write "cost".</kidding>
> > Using
> >
> > 	static const char * const reset_reason_array[] = {
> >
> > should do the trick.
> 
> No, it doesn't. Only this would:
> 
> static const bla[] = "this is a really constant string";
> static const char * const reset_reason_array[] = {
> 	[0] = bla,
> [...]
> };
What makes you think it's not const. I think it is, look:

	ukleinek@perseus:~/tmp$ cat test.c
	static const char * const const_reset_reason_array[] = {
		"jtag",
		"por",
	};

	static const char *reset_reason_array[] = {
		"jtag",
		"por",
	};

	void somefunc(void)
	{
		char *reason = const_reset_reason_array[0];
	}
	ukleinek@perseus:~/tmp$ gcc -Wall -c test.c
	test.c: In function ‘somefunc’:
	test.c:13:17: warning: initialization discards ‘const’ qualifier from pointer target type [enabled by default]
	test.c:13:8: warning: unused variable ‘reason’ [-Wunused-variable]
	test.c: At top level:
	test.c:6:20: warning: ‘reset_reason_array’ defined but not used [-Wunused-variable]

	ukleinek@perseus:~/tmp$ objdump -D -j .rodata -j .data test.o

	test.o:     file format elf64-x86-64


	Disassembly of section .data:

	0000000000000000 <reset_reason_array>:
		...

	Disassembly of section .rodata:

	0000000000000000 <const_reset_reason_array-0x10>:
	   0:	6a 74                	pushq  $0x74
	   2:	61                   	(bad)  
	   3:	67 00 70 6f          	add    %dh,0x6f(%eax)
	   7:	72 00                	jb     9 <const_reset_reason_array-0x7>
	   9:	00 00                	add    %al,(%rax)
	   b:	00 00                	add    %al,(%rax)
	   d:	00 00                	add    %al,(%rax)
		...

	0000000000000010 <const_reset_reason_array>:
		...

so const_reset_reason_array lives in .rodata and assinging
const_reset_reason_array[0] to a char * results in a warning.

What am I missing?

Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

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