[RFC] Add .bss.{init,exit} sections [take #2]

[RFC] Add .bss.{init,exit} sections [take #2]

[Franck Bui-Huu]

Hi,

It seems to magically work fine now. The init.bss section have been
renamed into .bss.init so GCC makes that section with nobits attribute.

I'm really not confident with these changes so if someone could
double check that would be great. Maybe it's time for asking some
advices to binutils mailing list ?

		Franck

[PATCH 1/4] Add .bss.{init,exit} sections

[Franck Bui-Huu]

This patch creates a new init section called .bss.init.

This section is similar to .init.data but doesn't consume
any space in the vmlinux image.

All data marked as part of this section must not be initialized,
of course.

Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
---
 include/linux/init.h |   25 +++++++++++++++++--------
 1 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/include/linux/init.h b/include/linux/init.h
index 74b1f43..0febf3e 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -43,6 +43,8 @@
 #define __init		__attribute__ ((__section__ (".init.text"))) __cold
 #define __initdata	__attribute__ ((__section__ (".init.data")))
 #define __exitdata	__attribute__ ((__section__(".exit.data")))
+#define __initbss	__attribute__ ((__section__ (".bss.init")))
+#define __exitbss	__attribute__ ((__section__ (".bss.exit")))
 #define __exit_call	__attribute_used__ __attribute__ ((__section__ (".exitcall.exit")))
 
 /* modpost check for section mismatches during the kernel build.
@@ -68,6 +70,7 @@
 #define __INIT		.section	".init.text","ax"
 #define __FINIT		.previous
 #define __INITDATA	.section	".init.data","aw"
+#define __INITBSS	.section	".bss.init","aw",@nobits
 
 #ifndef __ASSEMBLY__
 /*
@@ -257,10 +260,12 @@ void __init parse_early_param(void);
 #define __devexit
 #define __devexitdata
 #else
-#define __devinit __init
-#define __devinitdata __initdata
-#define __devexit __exit
-#define __devexitdata __exitdata
+#define __devinit	__init
+#define __devinitdata	__initdata
+#define __devinitbss	__initbss
+#define __devexit	__exit
+#define __devexitdata	__exitdata
+#define __devexitbss	__exitbss
 #endif
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -270,9 +275,11 @@ void __init parse_early_param(void);
 #define __cpuexitdata
 #else
 #define __cpuinit	__init
-#define __cpuinitdata __initdata
-#define __cpuexit __exit
+#define __cpuinitdata	__initdata
+#define __cpuinitbss	__initbss
+#define __cpuexit	__exit
 #define __cpuexitdata	__exitdata
+#define __cpuexitbss	__exitbss
 #endif
 
 #if defined(CONFIG_MEMORY_HOTPLUG) || defined(CONFIG_ACPI_HOTPLUG_MEMORY) \
@@ -283,9 +290,11 @@ void __init parse_early_param(void);
 #define __memexitdata
 #else
 #define __meminit	__init
-#define __meminitdata __initdata
-#define __memexit __exit
+#define __meminitdata	__initdata
+#define __meminitbss	__meminitbss
+#define __memexit	__exit
 #define __memexitdata	__exitdata
+#define __memexitbss	__exitbss
 #endif
 
 /* Functions marked as __devexit may be discarded at kernel link time, depending
-- 
1.5.3.4

[PATCH 2/4] Add .init.bss section for MIPS

[Franck Bui-Huu]

Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
---
 arch/mips/kernel/vmlinux.lds.S |   24 ++++++++++++++++--------
 1 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
index 84f9a4c..e0a4dc0 100644
--- a/arch/mips/kernel/vmlinux.lds.S
+++ b/arch/mips/kernel/vmlinux.lds.S
@@ -100,7 +100,7 @@ SECTIONS
 	_edata =  .;			/* End of data section */
 
 	/* will be freed after init */
-	. = ALIGN(_PAGE_SIZE);		/* Init code and data */
+	. = ALIGN(_PAGE_SIZE);		/* Init code, data and bss */
 	__init_begin = .;
 	.init.text : {
 		_sinittext = .;
@@ -148,19 +148,27 @@ SECTIONS
 	}
 #endif
 	PERCPU(_PAGE_SIZE)
-	. = ALIGN(_PAGE_SIZE);
-	__init_end = .;
-	/* freed after init ends here */
 
-	__bss_start = .;	/* BSS */
-	.sbss  : {
-		*(.sbss)
-		*(.scommon)
+	/*
+	 * Note that .bss.exit is also discarded at runtime for the
+	 * same reason as above.
+	 */
+	.bss.exit : {
+		*(.bss.exit)
 	}
+	__bss_start = .;	/* BSS */
 	.bss : {
+		*(.bss.init)
+		. = ALIGN(_PAGE_SIZE);
+		__init_end = .;		/* freed after init ends here */
+
 		*(.bss)
 		*(COMMON)
 	}
+	.sbss : {
+		*(.sbss)
+		*(.scommon)
+	}
 	__bss_stop = .;
 
 	_end = . ;
-- 
1.5.3.4

[PATCH 3/4] vmlinux.ld.S: correctly indent .data section

[Franck Bui-Huu]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 1550 bytes --]

Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
---
 arch/mips/kernel/vmlinux.lds.S |   32 +++++++++++++++++---------------
 1 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
index e0a4dc0..2f6c225 100644
--- a/arch/mips/kernel/vmlinux.lds.S
+++ b/arch/mips/kernel/vmlinux.lds.S
@@ -55,21 +55,23 @@ SECTIONS
 
 	/* writeable */
 	.data : {	/* Data */
-	  . = . + DATAOFFSET;		/* for CONFIG_MAPPED_KERNEL */
-	  /*
-	   * This ALIGN is needed as a workaround for a bug a gcc bug upto 4.1 which
-	   * limits the maximum alignment to at most 32kB and results in the following
-	   * warning:
-	   *
-	   *  CC      arch/mips/kernel/init_task.o
-	   * arch/mips/kernel/init_task.c:30: warning: alignment of ‘init_thread_union’
-	   * is greater than maximum object file alignment.  Using 32768
-	   */
-	  . = ALIGN(_PAGE_SIZE);
-	  *(.data.init_task)
-
-	  DATA_DATA
-	  CONSTRUCTORS
+		. = . + DATAOFFSET;		/* for CONFIG_MAPPED_KERNEL */
+		/*
+		 * This ALIGN is needed as a workaround for a bug a
+		 * gcc bug upto 4.1 which limits the maximum alignment
+		 * to at most 32kB and results in the following
+		 * warning:
+		 *
+		 *  CC      arch/mips/kernel/init_task.o
+		 * arch/mips/kernel/init_task.c:30: warning: alignment
+		 * of ‘init_thread_union’ is greater than maximum
+		 * object file alignment.  Using 32768
+		 */
+		. = ALIGN(_PAGE_SIZE);
+		*(.data.init_task)
+		
+		DATA_DATA
+		CONSTRUCTORS
 	}
 	_gp = . + 0x8000;
 	.lit8 : {
-- 
1.5.3.4

[PATCH 4/4] Use __bzero to clear .bss

[Franck Bui-Huu]

Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
---
 arch/mips/kernel/head.S |   11 ++++-------
 1 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/arch/mips/kernel/head.S b/arch/mips/kernel/head.S
index e46782b..330eec1 100644
--- a/arch/mips/kernel/head.S
+++ b/arch/mips/kernel/head.S
@@ -175,13 +175,10 @@ NESTED(kernel_entry, 16, sp)			# kernel entry point
 	mtc0	t0, CP0_STATUS
 #endif /* CONFIG_MIPS_MT_SMTC */
 
-	PTR_LA		t0, __bss_start		# clear .bss
-	LONG_S		zero, (t0)
-	PTR_LA		t1, __bss_stop - LONGSIZE
-1:
-	PTR_ADDIU	t0, LONGSIZE
-	LONG_S		zero, (t0)
-	bne		t0, t1, 1b
+	PTR_LA		a0, __bss_start		# clear .bss
+	PTR_LA		a1, __bss_stop
+	PTR_SUBU	a1, a0
+	jal		__bzero
 
 	LONG_S		a0, fw_arg0		# firmware arguments
 	LONG_S		a1, fw_arg1
-- 
1.5.3.4

Re: [PATCH 3/4] vmlinux.ld.S: correctly indent .data section

[Franck Bui-Huu]

Andrew Sharp wrote:
> On Thu, 18 Oct 2007 23:12:32 +0200 Franck Bui-Huu <fbuihuu@gmail.com>
> wrote:
> 
>> Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
>> ---
>>  arch/mips/kernel/vmlinux.lds.S |   32
>> +++++++++++++++++--------------- 1 files changed, 17 insertions(+),
>> 15 deletions(-)
>>
>> diff --git a/arch/mips/kernel/vmlinux.lds.S
>> b/arch/mips/kernel/vmlinux.lds.S index e0a4dc0..2f6c225 100644
>> --- a/arch/mips/kernel/vmlinux.lds.S
>> +++ b/arch/mips/kernel/vmlinux.lds.S
>> @@ -55,21 +55,23 @@ SECTIONS
>>  
>>  	/* writeable */
>>  	.data : {	/* Data */
>> -	  . = . + DATAOFFSET;		/* for
>> CONFIG_MAPPED_KERNEL */
>> -	  /*
>> -	   * This ALIGN is needed as a workaround for a bug a gcc
>> bug upto 4.1 which
>> -	   * limits the maximum alignment to at most 32kB and
>> results in the following
>> -	   * warning:
>> -	   *
>> -	   *  CC      arch/mips/kernel/init_task.o
>> -	   * arch/mips/kernel/init_task.c:30: warning: alignment of
>> â??init_thread_unionâ??
>> -	   * is greater than maximum object file alignment.  Using
>> 32768
>> -	   */
>> -	  . = ALIGN(_PAGE_SIZE);
>> -	  *(.data.init_task)
>> -
>> -	  DATA_DATA
>> -	  CONSTRUCTORS
>> +		. = . + DATAOFFSET;		/* for
>> CONFIG_MAPPED_KERNEL */
>> +		/*
>> +		 * This ALIGN is needed as a workaround for a bug a
>> +		 * gcc bug upto 4.1 which limits the maximum
> 
> at least fix the text while you're here: 'a bug a gcc bug'
> 
>> +		 * to at most 32kB and results in the following
>> +		 * warning:
>> +		 *
>> +		 *  CC      arch/mips/kernel/init_task.o
>> +		 * arch/mips/kernel/init_task.c:30: warning:
>> alignment
>> +		 * of â??init_thread_unionâ?? is greater than maximum
> 
> is that utf-8 or something?  probably should remove that.
> 
> sorry for the picayunes, but hey as long as you're here changing the
> indenting ~:^)
> 
> 

Okay I'll fix them.

Thanks
		Franck

Re: [PATCH 3/4] vmlinux.ld.S: correctly indent .data section

[Ralf Baechle]

On Thu, Oct 18, 2007 at 11:12:32PM +0200, Franck Bui-Huu wrote:

Thanks, applied.

  Ralf