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Fixing: char *foo = "blah";

KJ Felix Oxley 2 participants 2 messages Oct 7, 2005 Kernel janitors

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Felix Oxley

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Quoted 9 lines

From: Jeff Garzik <jgarzik at mandrakesoft dot com>

1) The string form

        [const] char *foo = "blah";

creates two variables in the final assembly output, a static string, and a char pointer to the static string. The alternate string form

Quoted 9 lines
        [const] char foo[] = "blah";

is better because it declares a single variable.

For variables marked __initdata, the "*foo" form causes only the pointer, not the string itself, to be dropped from the kernel image, which is a bug. Using the "foo[]" form with regular 'ole local variables also makes the assembly shorter.

I plan to take on this task as described at:
http://www.kerneljanitors.org/TODO

I have a number of queries:

1. I presume that the [brackets] indicate that const is optional.

	Therefore the following needs correcting:
		char *foo = "blah";

2. I suppose that the following form would also need correcting:
static const char *foo = "blah"

3. Does the following (with an empty string) need correcting?

		[const] char *foo = "";

4. What about this?

		static const char *class_name[] = { "off","UBR","CBR","VBR","ABR" };

5. These changes are spread across the kernel code.
Do patches need to be submitted to individual subsystem maintainers, or will
a single patch be ok?

cheers,
felix

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#1 lore raw

Quoting Felix Oxley <[email protected]>
Sent on Fri, 7 Oct 2005 12:34:03 +0100

Hello,

Quoted 14 lines

I plan to take on this task as described at:
http://www.kerneljanitors.org/TODO
I have a number of queries:

1. I presume that the [brackets] indicate that const is optional.

	Therefore the following needs correcting:
		char *foo = "blah";

2. I suppose that the following form would also need correcting:
static const char *foo = "blah"

3. Does the following (with an empty string) need correcting?

		[const] char *foo = "";
Quoted 8 lines

4. What about this?

		static const char *class_name[] =

{ "off","UBR","CBR","VBR","ABR" };

5. These changes are spread across the kernel code.
Do patches need to be submitted to individual subsystem
maintainers, or will a single patch be ok?

By May, 2005, I was working on this. Alexey told me that besides what gcc should do, I had to confirm that the change made was actually better.

In some cases, it was not. I've made a testcase, and the results were pretty odd (I was expecting something else):

http://lists.osdl.org/pipermail/kernel-janitors/2005-May/004146.html

Different versions of gcc and cross-compilers should produce different results. I really don't know yet what is the best case (ie, which is good for (almost) all architectures/compilers).

Anyone?

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Ricardo Nabinger Sanchez
GNU/Linux #140696 [http://counter.li.org]
Slackware Linux + FreeBSD

  Left to themselves, things tend to go from bad to worse.

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