linux-kernel - Re: [patch 1/7] Immediate Values - Architecture Independent Code

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Message-ID: <20070918175902.GB2915@Krystal>
Date:	Tue, 18 Sep 2007 13:59:02 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/7] Immediate Values - Architecture Independent Code

* Denys Vlasenko (vda.linux@...glemail.com) wrote:
> On Monday 17 September 2007 19:42, Mathieu Desnoyers wrote:
> > Index: linux-2.6-lttng/include/asm-generic/vmlinux.lds.h
> > ===================================================================
> > --- linux-2.6-lttng.orig/include/asm-generic/vmlinux.lds.h	2007-09-17 13:25:06.000000000 -0400
> > +++ linux-2.6-lttng/include/asm-generic/vmlinux.lds.h	2007-09-17 13:35:50.000000000 -0400
> > @@ -122,6 +122,13 @@
> >  		VMLINUX_SYMBOL(__stop___kcrctab_gpl_future) = .;	\
> >  	}								\
> >  									\
> > +	/* Immediate values: pointers */				\
> > +	__immediate : AT(ADDR(__immediate) - LOAD_OFFSET) {		\
> > +		VMLINUX_SYMBOL(__start___immediate) = .;		\
> > +		*(__immediate)						\
> > +		VMLINUX_SYMBOL(__stop___immediate) = .;			\
> > +	}								\
> > +									\
> 
> Why do you need an output section for that? IOW: will this work too?
> 
> .data : ... { 
> ...
> 
> 		VMLINUX_SYMBOL(__start___immediate) = .;		\
> 		*(__immediate)						\
> 		VMLINUX_SYMBOL(__stop___immediate) = .;			\
> ...
> }
> 

This last one could cause alignment problems. We either have to use the
proper ALIGN() before the section, or let AT(ADDR(__immediate) -
LOAD_OFFSET) take care of it. I prefer the latter.

> 
> > Index: linux-2.6-lttng/kernel/module.c
> > ===================================================================
> > --- linux-2.6-lttng.orig/kernel/module.c	2007-09-17 13:25:06.000000000 -0400
> > +++ linux-2.6-lttng/kernel/module.c	2007-09-17 13:35:51.000000000 -0400
> > @@ -33,6 +33,7 @@
> >  #include <linux/cpu.h>
> >  #include <linux/moduleparam.h>
> >  #include <linux/errno.h>
> > +#include <linux/immediate.h>
> >  #include <linux/err.h>
> >  #include <linux/vermagic.h>
> >  #include <linux/notifier.h>
> > @@ -1717,6 +1718,7 @@ static struct module *load_module(void _
> >  	unsigned int unusedcrcindex;
> >  	unsigned int unusedgplindex;
> >  	unsigned int unusedgplcrcindex;
> > +	unsigned int immediateindex;
> >  	struct module *mod;
> >  	long err = 0;
> >  	void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
> > @@ -1813,6 +1815,7 @@ static struct module *load_module(void _
> >  #ifdef ARCH_UNWIND_SECTION_NAME
> >  	unwindex = find_sec(hdr, sechdrs, secstrings, ARCH_UNWIND_SECTION_NAME);
> >  #endif
> > +	immediateindex = find_sec(hdr, sechdrs, secstrings, "__immediate");
> 
> 
> Do you need to frame immediateindex by #ifdef CONFIG_IMMEDIATE / #endif?

I could, but I have been told to leave the immediateindex there even though
immediate values are configured out. I guess visual hideousness is the
main argument there.

Mathieu

> --
> vda

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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