Skip to contentSkip to conversation

kernel: call constructors

RFC PATCH In review Peter Oberparleiter 3 participants 5 messages May 5, 2008 – May 6, 2008

Subsystems (3)
PowerPC Generic include/asm header files Module support
lore
Share & tools
lore

Peter Oberparleiter

author
#0 lore raw

RFC PATCH 1/6 kernel: call constructors

From: Peter Oberparleiter <[email protected]>

Call constructors during kernel init and module load. Required by the gcov profiling infrastructure: gcc's profiling code uses constructors to register profiling data structures.

Signed-off-by Peter Oberparleiter <[email protected]>
---
 arch/powerpc/kernel/vmlinux.lds.S |    3 +++
 include/asm-generic/sections.h    |    1 +
 include/asm-generic/vmlinux.lds.h |    8 ++++++++
 include/linux/module.h            |    5 +++++
 init/main.c                       |   10 ++++++++++
 kernel/module.c                   |   13 +++++++++++++
 6 files changed, 40 insertions(+)
include/asm-generic/vmlinux.lds.h +8 -0
Index: linux-2.6.26-rc1/include/asm-generic/vmlinux.lds.h
===================================================================
@@ -352,3 +352,11 @@
 		*(.data.percpu.shared_aligned)				\
 	}								\
 	__per_cpu_end = .;
+
+#define CONSTRUCTORS							\
+		__CTOR_LIST__ = .;					\
+		*(.ctors)						\
+		__CTOR_END__ = .;					\
+		__DTOR_LIST__ = .;					\
+		*(.dtors)						\
+		__DTOR_END__ = .;
arch/powerpc/kernel/vmlinux.lds.S +3 -0
Index: linux-2.6.26-rc1/arch/powerpc/kernel/vmlinux.lds.S
===================================================================
@@ -193,6 +193,9 @@ SECTIONS
 		*(.toc)
 	}
 #endif
+	.data.gcov : {
+		CONSTRUCTORS
+	}
 
 	. = ALIGN(PAGE_SIZE);
 	_edata  =  .;
include/asm-generic/sections.h +1 -0
Index: linux-2.6.26-rc1/include/asm-generic/sections.h
===================================================================
@@ -13,5 +13,6 @@ extern char __per_cpu_start[], __per_cpu
 extern char __kprobes_text_start[], __kprobes_text_end[];
 extern char __initdata_begin[], __initdata_end[];
 extern char __start_rodata[], __end_rodata[];
+extern char __CTOR_LIST__[], __CTOR_END__[];
 
 #endif /* _ASM_GENERIC_SECTIONS_H_ */
include/linux/module.h +5 -0
Index: linux-2.6.26-rc1/include/linux/module.h
===================================================================
@@ -229,6 +229,8 @@ enum module_state
 	MODULE_STATE_GOING,
 };
 
+typedef void (*ctorcall_t)(void);
+
 struct module
 {
 	enum module_state state;

@@ -342,6 +344,9 @@ struct module
 	struct marker *markers;
 	unsigned int num_markers;
 #endif
+	/* Constructor calls. */
+	ctorcall_t *ctors;
+	unsigned long num_ctors;
 };
 #ifndef MODULE_ARCH_INIT
 #define MODULE_ARCH_INIT {}
kernel/module.c +13 -0
Index: linux-2.6.26-rc1/kernel/module.c
===================================================================
@@ -1736,6 +1736,7 @@ static struct module *load_module(void _
 	unsigned int unusedgplcrcindex;
 	unsigned int markersindex;
 	unsigned int markersstringsindex;
+	unsigned int ctorsindex;
 	struct module *mod;
 	long err = 0;
 	void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */

@@ -1832,6 +1833,7 @@ static struct module *load_module(void _
 #ifdef ARCH_UNWIND_SECTION_NAME
 	unwindex = find_sec(hdr, sechdrs, secstrings, ARCH_UNWIND_SECTION_NAME);
 #endif
+	ctorsindex = find_sec(hdr, sechdrs, secstrings, ".ctors");
 
 	/* Don't keep modinfo and version sections. */
 	sechdrs[infoindex].sh_flags &= ~(unsigned long)SHF_ALLOC;

@@ -2041,6 +2043,8 @@ static struct module *load_module(void _
 	mod->num_markers =
 		sechdrs[markersindex].sh_size / sizeof(*mod->markers);
 #endif
+	mod->ctors = (void *) sechdrs[ctorsindex].sh_addr;
+	mod->num_ctors = sechdrs[ctorsindex].sh_size / sizeof(*mod->ctors);
 
         /* Find duplicate symbols */
 	err = verify_export_symbols(mod);

@@ -2153,6 +2157,14 @@ static struct module *load_module(void _
 	goto free_hdr;
 }
 
+static void do_mod_ctors(struct module *mod)
+{
+	unsigned long i;
+
+	for (i = 0; i < mod->num_ctors; i++)
+		mod->ctors[i]();
+}
+
 /* This is where the real work happens */
 asmlinkage long
 sys_init_module(void __user *umod,

@@ -2183,6 +2195,7 @@ sys_init_module(void __user *umod,
 	blocking_notifier_call_chain(&module_notify_list,
 			MODULE_STATE_COMING, mod);
 
+	do_mod_ctors(mod);
 	/* Start the module */
 	if (mod->init != NULL)
 		ret = mod->init();
init/main.c +10 -0
Index: linux-2.6.26-rc1/init/main.c
===================================================================
@@ -683,6 +683,15 @@ asmlinkage void __init start_kernel(void
 	rest_init();
 }
 
+static void __init do_ctors(void)
+{
+	ctorcall_t *call;
+
+	for (call = (ctorcall_t *) __CTOR_LIST__;
+	     call < (ctorcall_t *) __CTOR_END__; call++)
+		(*call)();
+}
+
 static int __initdata initcall_debug;
 
 static int __init initcall_debug_setup(char *str)

@@ -760,6 +769,7 @@ static void __init do_basic_setup(void)
 	usermodehelper_init();
 	driver_init();
 	init_irq_proc();
+	do_ctors();
 	do_initcalls();
 }
#1 lore raw
Quoted 22 lines · Peter Oberparleiter

From: Peter Oberparleiter <[email protected]>

Call constructors during kernel init and module load. Required by the gcov profiling infrastructure: gcc's profiling code uses constructors to register profiling data structures.

Signed-off-by Peter Oberparleiter <[email protected]>
---
 arch/powerpc/kernel/vmlinux.lds.S |    3 +++
 include/asm-generic/sections.h    |    1 +
 include/asm-generic/vmlinux.lds.h |    8 ++++++++
 include/linux/module.h            |    5 +++++
 init/main.c                       |   10 ++++++++++
 kernel/module.c                   |   13 +++++++++++++
 6 files changed, 40 insertions(+)

Index: linux-2.6.26-rc1/include/asm-generic/vmlinux.lds.h
===================================================================

include/asm-generic/vmlinux.lds.h +0 -0
@@ -352,3 +352,11 @@
 		*(.data.percpu.shared_aligned)				\

include/asm-generic/vmlinux.lds.h line 362

Quoted 10 lines
include/asm-generic/vmlinux.lds.h +8 -0
 	}								\
 	__per_cpu_end = .;
+
+#define CONSTRUCTORS							\
+		__CTOR_LIST__ = .;					\
+		*(.ctors)						\
+		__CTOR_END__ = .;					\
+		__DTOR_LIST__ = .;					\
+		*(.dtors)						\
+		__DTOR_END__ = .;

You shall use: VMLINUX_SYMBOL() here.
And why those SHOUTING names?
All other linker symbols are lowercase.

Quoted 130 lines

Index: linux-2.6.26-rc1/arch/powerpc/kernel/vmlinux.lds.S
===================================================================

arch/powerpc/kernel/vmlinux.lds.S +3 -0
@@ -193,6 +193,9 @@ SECTIONS
 		*(.toc)
 	}
 #endif
+	.data.gcov : {
+		CONSTRUCTORS
+	}
 
 	. = ALIGN(PAGE_SIZE);
 	_edata  =  .;

Index: linux-2.6.26-rc1/include/asm-generic/sections.h
===================================================================

include/asm-generic/sections.h +1 -0
@@ -13,5 +13,6 @@ extern char __per_cpu_start[], __per_cpu
 extern char __kprobes_text_start[], __kprobes_text_end[];
 extern char __initdata_begin[], __initdata_end[];
 extern char __start_rodata[], __end_rodata[];
+extern char __CTOR_LIST__[], __CTOR_END__[];
 
 #endif /* _ASM_GENERIC_SECTIONS_H_ */

Index: linux-2.6.26-rc1/include/linux/module.h
===================================================================

include/linux/module.h +5 -0
@@ -229,6 +229,8 @@ enum module_state
 	MODULE_STATE_GOING,
 };
 
+typedef void (*ctorcall_t)(void);
+
 struct module
 {
 	enum module_state state;

@@ -342,6 +344,9 @@ struct module
 	struct marker *markers;
 	unsigned int num_markers;
 #endif
+	/* Constructor calls. */
+	ctorcall_t *ctors;
+	unsigned long num_ctors;
 };
 #ifndef MODULE_ARCH_INIT
 #define MODULE_ARCH_INIT {}

Index: linux-2.6.26-rc1/kernel/module.c
===================================================================

kernel/module.c +13 -0
@@ -1736,6 +1736,7 @@ static struct module *load_module(void _
 	unsigned int unusedgplcrcindex;
 	unsigned int markersindex;
 	unsigned int markersstringsindex;
+	unsigned int ctorsindex;
 	struct module *mod;
 	long err = 0;
 	void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */

@@ -1832,6 +1833,7 @@ static struct module *load_module(void _
 #ifdef ARCH_UNWIND_SECTION_NAME
 	unwindex = find_sec(hdr, sechdrs, secstrings, ARCH_UNWIND_SECTION_NAME);
 #endif
+	ctorsindex = find_sec(hdr, sechdrs, secstrings, ".ctors");
 
 	/* Don't keep modinfo and version sections. */
 	sechdrs[infoindex].sh_flags &= ~(unsigned long)SHF_ALLOC;

@@ -2041,6 +2043,8 @@ static struct module *load_module(void _
 	mod->num_markers =
 		sechdrs[markersindex].sh_size / sizeof(*mod->markers);
 #endif
+	mod->ctors = (void *) sechdrs[ctorsindex].sh_addr;
+	mod->num_ctors = sechdrs[ctorsindex].sh_size / sizeof(*mod->ctors);
 
         /* Find duplicate symbols */
 	err = verify_export_symbols(mod);

@@ -2153,6 +2157,14 @@ static struct module *load_module(void _
 	goto free_hdr;
 }
 
+static void do_mod_ctors(struct module *mod)
+{
+	unsigned long i;
+
+	for (i = 0; i < mod->num_ctors; i++)
+		mod->ctors[i]();
+}
+
 /* This is where the real work happens */
 asmlinkage long
 sys_init_module(void __user *umod,

@@ -2183,6 +2195,7 @@ sys_init_module(void __user *umod,
 	blocking_notifier_call_chain(&module_notify_list,
 			MODULE_STATE_COMING, mod);
 
+	do_mod_ctors(mod);
 	/* Start the module */
 	if (mod->init != NULL)
 		ret = mod->init();

Index: linux-2.6.26-rc1/init/main.c
===================================================================

init/main.c +10 -0
@@ -683,6 +683,15 @@ asmlinkage void __init start_kernel(void
 	rest_init();
 }
 
+static void __init do_ctors(void)
+{
+	ctorcall_t *call;
+
+	for (call = (ctorcall_t *) __CTOR_LIST__;
+	     call < (ctorcall_t *) __CTOR_END__; call++)
+		(*call)();
+}
+
 static int __initdata initcall_debug;
 
 static int __init initcall_debug_setup(char *str)

@@ -760,6 +769,7 @@ static void __init do_basic_setup(void)
 	usermodehelper_init();
 	driver_init();
 	init_irq_proc();
+	do_ctors();
 	do_initcalls();
 }
author
#2 lore raw
Quoted 11 lines · Sam Ravnborg

include/asm-generic/vmlinux.lds.h line 362

Quoted 8 lines · Peter Oberparleiter

From: Peter Oberparleiter <[email protected]>

include/asm-generic/vmlinux.lds.h +7 -0
+#define CONSTRUCTORS							\
+		__CTOR_LIST__ = .;					\
+		*(.ctors)						\
+		__CTOR_END__ = .;					\
+		__DTOR_LIST__ = .;					\
+		*(.dtors)						\
+		__DTOR_END__ = .;

You shall use: VMLINUX_SYMBOL() here.

Ok, will do.

Quoted 2 lines

And why those SHOUTING names?
All other linker symbols are lowercase.

Here's the background for that: currently, almost all arch/*/vmlinux.lds.S scripts contain reference to a CONSTRUCTORS sections which is (as of yet) empty. The info pages for ld contain a description of the contents of this section (section 3.6.6 Output Section Keywords), including the following sample linker script:

                __CTOR_LIST__ = .;
                LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2)
                *(.ctors)
                LONG(0)
                __CTOR_END__ = .;
                __DTOR_LIST__ = .;
                LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2)
                *(.dtors)
                LONG(0)
                __DTOR_END__ = .;

Apparently this sample script is buggy (namely the divide by 4 bit on 64 bit systems) so I changed it into the version found in the patch. This is somewhat of a trade-off between the information which should be present in a CONSTRUCTORS section according to the info page and what really is needed to implement constructor support.

I guess changing the names would be an option if required, as well as dropping the (unused) destructor bit of the linker script.

#3 lore raw
In reply to Peter Oberparleiter
Quoted 6 lines · On Mon, 05 May 2008 17:24:04 +0200 Peter Oberparleiter…

From: Peter Oberparleiter <[email protected]>

Call constructors during kernel init and module load. Required by the gcov profiling infrastructure: gcc's profiling code uses constructors to register profiling data structures.

Looks sane.

Quoted 30 lines
---
 arch/powerpc/kernel/vmlinux.lds.S |    3 +++
 include/asm-generic/sections.h    |    1 +
 include/asm-generic/vmlinux.lds.h |    8 ++++++++
 include/linux/module.h            |    5 +++++
 init/main.c                       |   10 ++++++++++
 kernel/module.c                   |   13 +++++++++++++
 6 files changed, 40 insertions(+)

Index: linux-2.6.26-rc1/include/asm-generic/vmlinux.lds.h
===================================================================

include/asm-generic/vmlinux.lds.h +8 -0
@@ -352,3 +352,11 @@
 		*(.data.percpu.shared_aligned)				\
 	}								\
 	__per_cpu_end = .;
+
+#define CONSTRUCTORS							\
+		__CTOR_LIST__ = .;					\
+		*(.ctors)						\
+		__CTOR_END__ = .;					\
+		__DTOR_LIST__ = .;					\
+		*(.dtors)						\
+		__DTOR_END__ = .;

Index: linux-2.6.26-rc1/arch/powerpc/kernel/vmlinux.lds.S
===================================================================

arch/powerpc/kernel/vmlinux.lds.S SECTIONS · line 198

Quoted 6 lines
arch/powerpc/kernel/vmlinux.lds.S +3 -0
@@ -193,6 +193,9 @@ SECTIONS
 		*(.toc)
 	}
 #endif
+	.data.gcov : {
+		CONSTRUCTORS
+	}

Why did powerpc (and only powerpc) need this touchup? It already includes asm-generic/vmlinux.lds.h?

Quoted 117 lines
arch/powerpc/kernel/vmlinux.lds.S +0 -0
 	. = ALIGN(PAGE_SIZE);
 	_edata  =  .;

Index: linux-2.6.26-rc1/include/asm-generic/sections.h
===================================================================

include/asm-generic/sections.h +1 -0
@@ -13,5 +13,6 @@ extern char __per_cpu_start[], __per_cpu
 extern char __kprobes_text_start[], __kprobes_text_end[];
 extern char __initdata_begin[], __initdata_end[];
 extern char __start_rodata[], __end_rodata[];
+extern char __CTOR_LIST__[], __CTOR_END__[];
 
 #endif /* _ASM_GENERIC_SECTIONS_H_ */

Index: linux-2.6.26-rc1/include/linux/module.h
===================================================================

include/linux/module.h +5 -0
@@ -229,6 +229,8 @@ enum module_state
 	MODULE_STATE_GOING,
 };
 
+typedef void (*ctorcall_t)(void);
+
 struct module
 {
 	enum module_state state;

@@ -342,6 +344,9 @@ struct module
 	struct marker *markers;
 	unsigned int num_markers;
 #endif
+	/* Constructor calls. */
+	ctorcall_t *ctors;
+	unsigned long num_ctors;
 };
 #ifndef MODULE_ARCH_INIT
 #define MODULE_ARCH_INIT {}

Index: linux-2.6.26-rc1/kernel/module.c
===================================================================

kernel/module.c +13 -0
@@ -1736,6 +1736,7 @@ static struct module *load_module(void _
 	unsigned int unusedgplcrcindex;
 	unsigned int markersindex;
 	unsigned int markersstringsindex;
+	unsigned int ctorsindex;
 	struct module *mod;
 	long err = 0;
 	void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */

@@ -1832,6 +1833,7 @@ static struct module *load_module(void _
 #ifdef ARCH_UNWIND_SECTION_NAME
 	unwindex = find_sec(hdr, sechdrs, secstrings, ARCH_UNWIND_SECTION_NAME);
 #endif
+	ctorsindex = find_sec(hdr, sechdrs, secstrings, ".ctors");
 
 	/* Don't keep modinfo and version sections. */
 	sechdrs[infoindex].sh_flags &= ~(unsigned long)SHF_ALLOC;

@@ -2041,6 +2043,8 @@ static struct module *load_module(void _
 	mod->num_markers =
 		sechdrs[markersindex].sh_size / sizeof(*mod->markers);
 #endif
+	mod->ctors = (void *) sechdrs[ctorsindex].sh_addr;
+	mod->num_ctors = sechdrs[ctorsindex].sh_size / sizeof(*mod->ctors);
 
         /* Find duplicate symbols */
 	err = verify_export_symbols(mod);

@@ -2153,6 +2157,14 @@ static struct module *load_module(void _
 	goto free_hdr;
 }
 
+static void do_mod_ctors(struct module *mod)
+{
+	unsigned long i;
+
+	for (i = 0; i < mod->num_ctors; i++)
+		mod->ctors[i]();
+}
+
 /* This is where the real work happens */
 asmlinkage long
 sys_init_module(void __user *umod,

@@ -2183,6 +2195,7 @@ sys_init_module(void __user *umod,
 	blocking_notifier_call_chain(&module_notify_list,
 			MODULE_STATE_COMING, mod);
 
+	do_mod_ctors(mod);
 	/* Start the module */
 	if (mod->init != NULL)
 		ret = mod->init();

Index: linux-2.6.26-rc1/init/main.c
===================================================================

init/main.c +10 -0
@@ -683,6 +683,15 @@ asmlinkage void __init start_kernel(void
 	rest_init();
 }
 
+static void __init do_ctors(void)
+{
+	ctorcall_t *call;
+
+	for (call = (ctorcall_t *) __CTOR_LIST__;
+	     call < (ctorcall_t *) __CTOR_END__; call++)
+		(*call)();
+}
+
 static int __initdata initcall_debug;
 
 static int __init initcall_debug_setup(char *str)

@@ -760,6 +769,7 @@ static void __init do_basic_setup(void)
 	usermodehelper_init();
 	driver_init();
 	init_irq_proc();
+	do_ctors();
 	do_initcalls();
 }
author
#4 lore raw
Quoted 15 lines · Andrew Morton

arch/powerpc/kernel/vmlinux.lds.S SECTIONS · line 198

Quoted 10 lines · On Mon, 05 May 2008 17:24:04 +0200 Peter Oberparleiter…

From: Peter Oberparleiter <[email protected]>

arch/powerpc/kernel/vmlinux.lds.S +3 -0
@@ -193,6 +193,9 @@ SECTIONS
 		*(.toc)
 	}
 #endif
+	.data.gcov : {
+		CONSTRUCTORS
+	}

Why did powerpc (and only powerpc) need this touchup? It already includes asm-generic/vmlinux.lds.h?

asm-generic/vmlinux.lds.h defines CONSTRUCTORS but it needs to be referenced in the actual linker script to become active. For some reason unknown to me, CONSTRUCTORS shows up in all arch/*/vmlinux.lds.S scripts except for powerpc (see also my other reply about the CONSTRUCTORS section).