On Wed, 30 May 2007 10:00:26 -0400 Mathieu Desnoyers <[EMAIL PROTECTED]> wrote:
> Conditional calls are used to compile in code that is meant to be dynamically > enabled at runtime. When code is disabled, it has a very small footprint. > > It has a generic cond_call version and optimized per architecture cond_calls. > The optimized cond_call uses a load immediate to remove a data cache hit. > > It adds a new rodata section "__cond_call" to place the pointers to the enable > value. > > cond_call activation functions sits in module.c. > The above doesn't really describe what these things are, nor what they are used for, nor how they actually work. It's all a bit of a mystery. The i386 implementation appears to be using self-modifying code, which is intriguing. <finds the documentation patch> OK, that helps somewhat. > --- > include/asm-generic/vmlinux.lds.h | 16 +- > include/linux/condcall.h | 91 +++++++++++++ > include/linux/module.h | 4 > kernel/module.c | 248 > ++++++++++++++++++++++++++++++++++++++ > 4 files changed, 356 insertions(+), 3 deletions(-) > > Index: linux-2.6-lttng/include/linux/condcall.h > =================================================================== > --- /dev/null 1970-01-01 00:00:00.000000000 +0000 > +++ linux-2.6-lttng/include/linux/condcall.h 2007-05-17 02:13:53.000000000 > -0400 > @@ -0,0 +1,91 @@ > +#ifndef _LINUX_CONDCALL_H > +#define _LINUX_CONDCALL_H > + > +/* > + * Conditional function calls. Cheap when disabled, enabled at runtime. > + * > + * (C) Copyright 2007 Mathieu Desnoyers <[EMAIL PROTECTED]> > + * > + * This file is released under the GPLv2. > + * See the file COPYING for more details. > + */ > + > +#ifdef __KERNEL__ > + > +struct __cond_call_struct { > + const char *name; > + void *enable; > + int flags; > +} __attribute__((packed)); Please document data structures lavishly. > + > +/* Cond call flags : selects the mechanism used to enable the conditional > calls > + * and prescribe what can be executed within their function. This is > primarily > + * used at reentrancy-unfriendly sites. */ You consistently use the wrong commenting style. We prefer /* Cond call flags : selects the mechanism used to enable the conditional calls * and prescribe what can be executed within their function. This is primarily * used at reentrancy-unfriendly sites. */ or /* * Cond call flags : selects the mechanism used to enable the conditional calls * and prescribe what can be executed within their function. This is primarily * used at reentrancy-unfriendly sites. */ > +#ifdef CONFIG_COND_CALL_ENABLE_OPTIMIZATION > +#include <asm/condcall.h> /* optimized cond_call flavor */ > +#else > +#include <asm-generic/condcall.h> /* fallback on generic cond_call */ > +#endif The preferred way to do this is to give every architecture an asm/condcall.h and from within that, include asm-generic/condcall.h. Your [patch 3/9] does most of that, but it didn't remove the above ifdef, and I don't think it removed the should-be-unneeded CONFIG_COND_CALL_ENABLE_OPTIMIZATION either? > +#define COND_CALL_MAX_FORMAT_LEN 1024 > + > +extern int cond_call_arm(const char *name); > +extern int cond_call_disarm(const char *name); > + > +/* cond_call_query : Returns 1 if enabled, 0 if disabled or not present */ > +extern int cond_call_query(const char *name); > +extern int cond_call_list(const char *name); > + > +#endif /* __KERNEL__ */ > +#endif > Index: linux-2.6-lttng/include/asm-generic/vmlinux.lds.h > =================================================================== > --- linux-2.6-lttng.orig/include/asm-generic/vmlinux.lds.h 2007-05-17 > 02:12:25.000000000 -0400 > +++ linux-2.6-lttng/include/asm-generic/vmlinux.lds.h 2007-05-17 > 02:13:42.000000000 -0400 > @@ -116,11 +116,22 @@ > *(__kcrctab_gpl_future) \ > VMLINUX_SYMBOL(__stop___kcrctab_gpl_future) = .; \ > } \ > - \ > + /* Conditional calls: pointers */ \ > + __cond_call : AT(ADDR(__cond_call) - LOAD_OFFSET) { \ > + VMLINUX_SYMBOL(__start___cond_call) = .; \ > + *(__cond_call) \ > + VMLINUX_SYMBOL(__stop___cond_call) = .; \ > + } \ > /* Kernel symbol table: strings */ \ > __ksymtab_strings : AT(ADDR(__ksymtab_strings) - LOAD_OFFSET) { > \ > *(__ksymtab_strings) \ > - } \ > + } \ > + /* Conditional calls: strings */ \ > + __cond_call_strings : AT(ADDR(__cond_call_strings) - LOAD_OFFSET) { \ whitespace went bad here. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/