linux-kernel - Re: [RFC PATCH 0/3] Mark literal strings in __init / _

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Message-ID: <1403638620.29061.35.camel@joe-AO725>
Date:	Tue, 24 Jun 2014 12:37:00 -0700
From:	Joe Perches <joe@...ches.com>
To:	Mathias Krause <minipli@...glemail.com>
Cc:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC PATCH 0/3] Mark literal strings in __init / __exit code

On Tue, 2014-06-24 at 21:13 +0200, Mathias Krause wrote:
> On 24 June 2014 16:31, Rasmus Villemoes <linux@...musvillemoes.dk> wrote:
[]
> > gcc already seems to contain infrastructure for this kind of thing, so
> > maybe it doesn't even require a plugin, but simply a little coordination
> > with the gcc folks. This snippet from gcc internals seems relevant:
> >
> > -- Target Hook: section * TARGET_ASM_FUNCTION_RODATA_SECTION (tree
> >           DECL)
> >      Return the readonly data section associated with 'DECL_SECTION_NAME
> >      (DECL)'.  The default version of this function selects
> >      '.gnu.linkonce.r.name' if the function's section is
> >      '.gnu.linkonce.t.name', '.rodata.name' if function is in
> >      '.text.name', and the normal readonly-data section otherwise.
> >
> 
> I don't think it's that easy. You cannot simply put all strings into
> the .init.rodata section when code currently gets emitted to
> .init.text. The reason is because strings used in __init code might be
> referenced later on, too. For example, the name passed to
> class_create() won't be copied. If that one would go into the
> .init.rodata section automatically, we would have dangling pointers
> after the .init.* memory got freed. Therefore a compiler driven
> approach would need to be implemented as a compiler extension, a gcc
> plugin to handle such cases -- know when a string can safely be put
> into the .init.rodata section and when not. But that decision is not
> as easy as Joe might think it would be. How would the plugin know
> which strings to put into the .init.rodata section? Would it only
> handle the ones passed to printk()?

Yes.

> I still strongly believe it's better to do this manually.

Maybe.

It'd work with any version of the compiler that way too.

It's a pretty simple transform.

I believe this will show most all of the __init
uses of printks:

$ grep-2.5.4 -rP --include=*.[ch] -n '\b__init\b[^\n][^\}]+\n}' * | \
  grep -P '^[\w\/\.]+:\d+:|\bprintk\b|\bpr_[a-z]+' | \
  grep -P -B1 '\bprintk\b|\bpr_[a-z]+'

This shows a little more than a 1000 __init printks
treewide that could be converted.

For example:
arch/ia64/include/asm/cyclone.h:6:extern void __init cyclone_setup(void);
        printk(KERN_ERR "Cyclone Counter: System not configured"
--
arch/ia64/kernel/acpi.c:66:static unsigned long __init acpi_find_rsdp(void)
                printk(KERN_WARNING PREFIX
--
arch/ia64/kernel/acpi.c:366:static int __init acpi_parse_madt(struct acpi_table
        printk(KERN_INFO PREFIX "Local APIC address %p\n", ipi_base_addr);

etc...

There are maybe 200 or so __exit ones.


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