[RFC PATCH 1/6] kernel: call constructors

[RFC PATCH 1/6] kernel: call constructors

[Peter Oberparleiter]

From: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>

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 <peter.oberparleiter@de.ibm.com>
---
 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
===================================================================
--- linux-2.6.26-rc1.orig/include/asm-generic/vmlinux.lds.h
+++ 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__ = .;
Index: linux-2.6.26-rc1/arch/powerpc/kernel/vmlinux.lds.S
===================================================================
--- linux-2.6.26-rc1.orig/arch/powerpc/kernel/vmlinux.lds.S
+++ 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  =  .;
Index: linux-2.6.26-rc1/include/asm-generic/sections.h
===================================================================
--- linux-2.6.26-rc1.orig/include/asm-generic/sections.h
+++ 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_ */
Index: linux-2.6.26-rc1/include/linux/module.h
===================================================================
--- linux-2.6.26-rc1.orig/include/linux/module.h
+++ 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 {}
Index: linux-2.6.26-rc1/kernel/module.c
===================================================================
--- linux-2.6.26-rc1.orig/kernel/module.c
+++ 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();
Index: linux-2.6.26-rc1/init/main.c
===================================================================
--- linux-2.6.26-rc1.orig/init/main.c
+++ 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();
 }
 

Re: [RFC PATCH 1/6] kernel: call constructors

[Sam Ravnborg]

On Mon, May 05, 2008 at 05:24:04PM +0200, Peter Oberparleiter wrote:
> From: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
> 
> 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 <peter.oberparleiter@de.ibm.com>
> ---
>  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
> ===================================================================
> --- linux-2.6.26-rc1.orig/include/asm-generic/vmlinux.lds.h
> +++ 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__ = .;

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

> Index: linux-2.6.26-rc1/arch/powerpc/kernel/vmlinux.lds.S
> ===================================================================
> --- linux-2.6.26-rc1.orig/arch/powerpc/kernel/vmlinux.lds.S
> +++ 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  =  .;
> Index: linux-2.6.26-rc1/include/asm-generic/sections.h
> ===================================================================
> --- linux-2.6.26-rc1.orig/include/asm-generic/sections.h
> +++ 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_ */
> Index: linux-2.6.26-rc1/include/linux/module.h
> ===================================================================
> --- linux-2.6.26-rc1.orig/include/linux/module.h
> +++ 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 {}
> Index: linux-2.6.26-rc1/kernel/module.c
> ===================================================================
> --- linux-2.6.26-rc1.orig/kernel/module.c
> +++ 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();
> Index: linux-2.6.26-rc1/init/main.c
> ===================================================================
> --- linux-2.6.26-rc1.orig/init/main.c
> +++ 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();
>  }
>  
> 
> 

Re: [RFC PATCH 1/6] kernel: call constructors

[Andrew Morton]

On Mon, 05 May 2008 17:24:04 +0200 Peter Oberparleiter <peter.oberparleiter@de.ibm.com> wrote:

> From: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
> 
> 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.

> ---
>  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
> ===================================================================
> --- linux-2.6.26-rc1.orig/include/asm-generic/vmlinux.lds.h
> +++ 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__ = .;
> Index: linux-2.6.26-rc1/arch/powerpc/kernel/vmlinux.lds.S
> ===================================================================
> --- linux-2.6.26-rc1.orig/arch/powerpc/kernel/vmlinux.lds.S
> +++ linux-2.6.26-rc1/arch/powerpc/kernel/vmlinux.lds.S
> @@ -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?

>  	. = ALIGN(PAGE_SIZE);
>  	_edata  =  .;
> Index: linux-2.6.26-rc1/include/asm-generic/sections.h
> ===================================================================
> --- linux-2.6.26-rc1.orig/include/asm-generic/sections.h
> +++ 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_ */
> Index: linux-2.6.26-rc1/include/linux/module.h
> ===================================================================
> --- linux-2.6.26-rc1.orig/include/linux/module.h
> +++ 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 {}
> Index: linux-2.6.26-rc1/kernel/module.c
> ===================================================================
> --- linux-2.6.26-rc1.orig/kernel/module.c
> +++ 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();
> Index: linux-2.6.26-rc1/init/main.c
> ===================================================================
> --- linux-2.6.26-rc1.orig/init/main.c
> +++ 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();
>  }
>  
> 

Re: [RFC PATCH 1/6] kernel: call constructors

[Peter Oberparleiter]

Sam Ravnborg wrote:
> On Mon, May 05, 2008 at 05:24:04PM +0200, Peter Oberparleiter wrote:
>> From: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
>> +#define CONSTRUCTORS							\
>> +		__CTOR_LIST__ = .;					\
>> +		*(.ctors)						\
>> +		__CTOR_END__ = .;					\
>> +		__DTOR_LIST__ = .;					\
>> +		*(.dtors)						\
>> +		__DTOR_END__ = .;
> 
> You shall use:  VMLINUX_SYMBOL() here.

Ok, will do.

> 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.

Re: [RFC PATCH 1/6] kernel: call constructors

[Peter Oberparleiter]

Andrew Morton wrote:
> On Mon, 05 May 2008 17:24:04 +0200 Peter Oberparleiter <peter.oberparleiter@de.ibm.com> wrote:
> 
>> From: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
>> --- linux-2.6.26-rc1.orig/arch/powerpc/kernel/vmlinux.lds.S
>> +++ linux-2.6.26-rc1/arch/powerpc/kernel/vmlinux.lds.S
>> @@ -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).