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Subject[patch 1/9] Conditional Calls - Architecture Independent Code
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.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
---
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 <mathieu.desnoyers@polymtl.ca>
+ *
+ * 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));
+
+
+/* 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. */
+#define CF_OPTIMIZED (1 << 0) /* Use optimized cond_call */
+#define CF_LOCKDEP (1 << 1) /* Can call lockdep */
+#define CF_PRINTK (1 << 2) /* Probe can call vprintk */
+#define CF_STATIC_ENABLE (1 << 3) /* Enable cond_call statically */
+#define _CF_NR 4
+
+#ifdef CONFIG_COND_CALL
+
+/* Generic cond_call flavor always available.
+ * Note : the empty asm volatile with read constraint is used here instead of a
+ * "used" attribute to fix a gcc 4.1.x bug. */
+#define cond_call_generic(flags, name, func) \
+ ({ \
+ static const char __cstrtab_name_##name[] \
+ __attribute__((section("__cond_call_strings"))) = #name; \
+ static char __cond_call_enable_##name = \
+ (flags) & CF_STATIC_ENABLE; \
+ static const struct __cond_call_struct __cond_call_##name \
+ __attribute__((section("__cond_call"))) = \
+ { __cstrtab_name_##name, \
+ &__cond_call_enable_##name, \
+ (flags) & ~CF_OPTIMIZED } ; \
+ asm volatile ( "" : : "i" (&__cond_call_##name)); \
+ (unlikely(__cond_call_enable_##name)) ? \
+ (func) : \
+ (__typeof__(func))0; \
+ })
+
+#define COND_CALL_GENERIC_ENABLE_IMMEDIATE_OFFSET 0
+#define COND_CALL_GENERIC_ENABLE_TYPE unsigned char
+/* Dereference enable as lvalue from a pointer to its instruction */
+#define COND_CALL_GENERIC_ENABLE(a) \
+ *(COND_CALL_GENERIC_ENABLE_TYPE*) \
+ ((char*)a+COND_CALL_GENERIC_ENABLE_IMMEDIATE_OFFSET)
+
+static inline int cond_call_generic_set_enable(void *address, char enable)
+{
+ COND_CALL_GENERIC_ENABLE(address) = enable;
+ return 0;
+}
+
+#else /* !CONFIG_COND_CALL */
+#define cond_call_generic(flags, name, func) \
+ ({ \
+ ((flags) & CF_STATIC_ENABLE) ? \
+ (func) : \
+ (__typeof__(func))0; \
+ })
+#endif /* CONFIG_COND_CALL */
+
+#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
+
+#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) { \
+ *(__cond_call_strings) \
+ } \
+ __end_rodata = .; \
+ . = ALIGN(4096); \
\
/* Built-in module parameters. */ \
__param : AT(ADDR(__param) - LOAD_OFFSET) { \
@@ -228,4 +239,3 @@
*(.initcall6s.init) \
*(.initcall7.init) \
*(.initcall7s.init)
-
Index: linux-2.6-lttng/include/linux/module.h
===================================================================
--- linux-2.6-lttng.orig/include/linux/module.h 2007-05-17 02:12:34.000000000 -0400
+++ linux-2.6-lttng/include/linux/module.h 2007-05-17 02:13:41.000000000 -0400
@@ -16,6 +16,7 @@
#include <linux/stringify.h>
#include <linux/kobject.h>
#include <linux/moduleparam.h>
+#include <linux/condcall.h>
#include <asm/local.h>

#include <asm/module.h>
@@ -356,6 +357,9 @@
/* The command line arguments (may be mangled). People like
keeping pointers to this stuff */
char *args;
+
+ const struct __cond_call_struct *cond_calls;
+ unsigned int num_cond_calls;
};
#ifndef MODULE_ARCH_INIT
#define MODULE_ARCH_INIT {}
Index: linux-2.6-lttng/kernel/module.c
===================================================================
--- linux-2.6-lttng.orig/kernel/module.c 2007-05-17 02:12:25.000000000 -0400
+++ linux-2.6-lttng/kernel/module.c 2007-05-17 02:13:53.000000000 -0400
@@ -32,6 +32,7 @@
#include <linux/cpu.h>
#include <linux/moduleparam.h>
#include <linux/errno.h>
+#include <linux/condcall.h>
#include <linux/err.h>
#include <linux/vermagic.h>
#include <linux/notifier.h>
@@ -141,6 +142,8 @@
extern const unsigned long __start___kcrctab_gpl_future[];
extern const unsigned long __start___kcrctab_unused[];
extern const unsigned long __start___kcrctab_unused_gpl[];
+extern const struct __cond_call_struct __start___cond_call[];
+extern const struct __cond_call_struct __stop___cond_call[];

#ifndef CONFIG_MODVERSIONS
#define symversion(base, idx) NULL
@@ -301,6 +304,230 @@
return NULL;
}

+#ifdef CONFIG_COND_CALL
+
+/* Set the enable bit of the cond_call, choosing the generic or architecture
+ * specific functions depending on the cond_call's flags.
+ */
+static int cond_call_set_enable(void *address, char enable, int flags)
+{
+ if (flags & CF_OPTIMIZED)
+ return cond_call_optimized_set_enable(address, enable);
+ else
+ return cond_call_generic_set_enable(address, enable);
+}
+
+/* Query the state of a cond_calls range. */
+static int _cond_call_query_range(const char *name,
+ const struct __cond_call_struct *begin,
+ const struct __cond_call_struct *end)
+{
+ const struct __cond_call_struct *iter;
+ int ret = 0;
+
+ for (iter = begin; iter < end; iter++) {
+ if (strcmp(name, iter->name) != 0)
+ continue;
+ if (iter->flags & CF_OPTIMIZED)
+ ret = COND_CALL_OPTIMIZED_ENABLE(iter->enable);
+ else
+ ret = COND_CALL_GENERIC_ENABLE(iter->enable);
+ if (ret)
+ break;
+ }
+ return ret;
+}
+
+/* Sets a range of cond_calls to a enabled state : set the enable bit. */
+static int _cond_call_arm_range(const char *name,
+ const struct __cond_call_struct *begin,
+ const struct __cond_call_struct *end)
+{
+ const struct __cond_call_struct *iter;
+ int found = 0;
+
+ for (iter = begin; iter < end; iter++) {
+ if (strcmp(name, iter->name) != 0)
+ continue;
+ cond_call_set_enable(iter->enable, 1, iter->flags);
+ found++;
+ }
+ return found;
+}
+
+/* Sets a range of cond_calls to a disabled state : unset the enable bit. */
+static int _cond_call_disarm_range(const char *name,
+ const struct __cond_call_struct *begin,
+ const struct __cond_call_struct *end)
+{
+ const struct __cond_call_struct *iter;
+ int found = 0;
+
+ for (iter = begin; iter < end; iter++) {
+ if (strcmp(name, iter->name) != 0)
+ continue;
+ cond_call_set_enable(iter->enable, 0, iter->flags);
+ found++;
+ }
+ return found;
+}
+
+/* Provides a listing of the cond_calls present in the kernel with their type
+ * (optimized or generic) and state (enabled or disabled). */
+static int _cond_call_list_range(const char *name,
+ const struct __cond_call_struct *begin,
+ const struct __cond_call_struct *end)
+{
+ const struct __cond_call_struct *iter;
+ int found = 0;
+
+ for (iter = begin; iter < end; iter++) {
+ if (name)
+ if (strcmp(name, iter->name) != 0)
+ continue;
+ printk("name %s \n", iter->name);
+ if (iter->flags & CF_OPTIMIZED)
+ printk(" enable %u optimized\n",
+ COND_CALL_OPTIMIZED_ENABLE(iter->enable));
+ else
+ printk(" enable %u generic\n",
+ COND_CALL_GENERIC_ENABLE(iter->enable));
+ found++;
+ }
+ return found;
+}
+
+/* Calls _cond_call_query_range for the core cond_calls and modules cond_calls.
+ */
+static int _cond_call_query(const char *name)
+{
+ struct module *mod;
+ int ret = 0;
+
+ /* Core kernel cond_calls */
+ ret = _cond_call_query_range(name,
+ __start___cond_call, __stop___cond_call);
+ if (ret)
+ return ret;
+ /* Cond_calls in modules. */
+ list_for_each_entry(mod, &modules, list) {
+ if (mod->taints)
+ continue;
+ ret = _cond_call_query_range(name,
+ mod->cond_calls, mod->cond_calls+mod->num_cond_calls);
+ if (ret)
+ break;
+ }
+ return ret;
+}
+
+/* Cond_call enabling/disabling use the module_mutex to synchronize.
+ * Returns 1 if enabled, 0 if disabled or not present. */
+int cond_call_query(const char *name)
+{
+ int ret = 0;
+
+ mutex_lock(&module_mutex);
+ ret = _cond_call_query(name);
+ mutex_unlock(&module_mutex);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(cond_call_query);
+
+/* Calls _cond_call_arm_range for the core cond_calls and modules cond_calls.
+ * FIXME : cond_call will not be active on modules loaded later than the
+ * cond_call_arm. */
+static int _cond_call_arm(const char *name)
+{
+ struct module *mod;
+ int found = 0;
+
+ /* Core kernel cond_calls */
+ found += _cond_call_arm_range(name,
+ __start___cond_call, __stop___cond_call);
+ /* Cond_calls in modules. */
+ list_for_each_entry(mod, &modules, list) {
+ if (mod->taints)
+ continue;
+ found += _cond_call_arm_range(name,
+ mod->cond_calls, mod->cond_calls+mod->num_cond_calls);
+ }
+ return found;
+}
+
+/* Cond_call enabling/disabling use the module_mutex to synchronize. */
+int cond_call_arm(const char *name)
+{
+ int found = 0;
+
+ mutex_lock(&module_mutex);
+ found = _cond_call_arm(name);
+ mutex_unlock(&module_mutex);
+ return found;
+}
+EXPORT_SYMBOL_GPL(cond_call_arm);
+
+/* Calls _cond_call_disarm_range for the core cond_calls and modules cond_calls.
+ */
+static int _cond_call_disarm(const char *name)
+{
+ struct module *mod;
+ int found = 0;
+
+ /* Core kernel cond_calls */
+ found += _cond_call_disarm_range(name,
+ __start___cond_call, __stop___cond_call);
+ /* Cond_calls in modules. */
+ list_for_each_entry(mod, &modules, list) {
+ if (mod->taints)
+ continue;
+ found += _cond_call_disarm_range(name,
+ mod->cond_calls, mod->cond_calls+mod->num_cond_calls);
+ }
+ return found;
+}
+
+/* Cond_call enabling/disabling use the module_mutex to synchronize. */
+int cond_call_disarm(const char *name)
+{
+ int found = 0;
+
+ mutex_lock(&module_mutex);
+ found = _cond_call_disarm(name);
+ mutex_unlock(&module_mutex);
+ return found;
+}
+EXPORT_SYMBOL_GPL(cond_call_disarm);
+
+/* Calls _cond_call_list_range for the core and module cond_calls.
+ * Cond call listing uses the module_mutex to synchronize.
+ * TODO : should output this listing to a procfs file. */
+int cond_call_list(const char *name)
+{
+ struct module *mod;
+ int found = 0;
+
+ mutex_lock(&module_mutex);
+ /* Core kernel cond_calls */
+ printk("Listing kernel cond_calls\n");
+ found += _cond_call_list_range(name,
+ __start___cond_call, __stop___cond_call);
+ /* Cond_calls in modules. */
+ printk("Listing module cond_calls\n");
+ list_for_each_entry(mod, &modules, list) {
+ if (!mod->taints) {
+ printk("Listing cond_calls for module %s\n", mod->name);
+ found += _cond_call_list_range(name, mod->cond_calls,
+ mod->cond_calls+mod->num_cond_calls);
+ }
+ }
+ mutex_unlock(&module_mutex);
+ return found;
+}
+EXPORT_SYMBOL_GPL(cond_call_list);
+
+#endif
+
#ifdef CONFIG_SMP
/* Number of blocks used and allocated. */
static unsigned int pcpu_num_used, pcpu_num_allocated;
@@ -1658,6 +1885,8 @@
unsigned int unusedcrcindex;
unsigned int unusedgplindex;
unsigned int unusedgplcrcindex;
+ unsigned int condcallindex;
+ unsigned int condcallstringsindex;
struct module *mod;
long err = 0;
void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
@@ -1754,6 +1983,8 @@
#ifdef ARCH_UNWIND_SECTION_NAME
unwindex = find_sec(hdr, sechdrs, secstrings, ARCH_UNWIND_SECTION_NAME);
#endif
+ condcallindex = find_sec(hdr, sechdrs, secstrings, "__cond_call");
+ condcallstringsindex = find_sec(hdr, sechdrs, secstrings, "__cond_call_strings");

/* Don't keep modinfo section */
sechdrs[infoindex].sh_flags &= ~(unsigned long)SHF_ALLOC;
@@ -1764,6 +1995,18 @@
#endif
if (unwindex)
sechdrs[unwindex].sh_flags |= SHF_ALLOC;
+#ifdef CONFIG_COND_CALL
+ if (condcallindex)
+ sechdrs[condcallindex].sh_flags |= SHF_ALLOC;
+ if (condcallstringsindex)
+ sechdrs[condcallstringsindex].sh_flags |= SHF_ALLOC;
+#else
+ if (condcallindex)
+ sechdrs[condcallindex].sh_flags &= ~(unsigned long)SHF_ALLOC;
+ if (condcallstringsindex)
+ sechdrs[condcallstringsindex].sh_flags
+ &= ~(unsigned long)SHF_ALLOC;
+#endif

/* Check module struct version now, before we try to use module. */
if (!check_modstruct_version(sechdrs, versindex, mod)) {
@@ -1904,6 +2147,11 @@
mod->gpl_future_syms = (void *)sechdrs[gplfutureindex].sh_addr;
if (gplfuturecrcindex)
mod->gpl_future_crcs = (void *)sechdrs[gplfuturecrcindex].sh_addr;
+ if (condcallindex) {
+ mod->cond_calls = (void *)sechdrs[condcallindex].sh_addr;
+ mod->num_cond_calls =
+ sechdrs[condcallindex].sh_size / sizeof(*mod->cond_calls);
+ }

mod->unused_syms = (void *)sechdrs[unusedindex].sh_addr;
if (unusedcrcindex)
--
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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