Re: [PATCH 0/4] __cpuinitconst and __devinitconst

On Fri, Jan 11, 2008 at 08:44:28PM +0100, Sam Ravnborg wrote:
Hi Jan.

On Fri, Jan 11, 2008 at 08:55:29AM +0000, Jan Beulich wrote:
Since __cpuinitdata/__devinitdata don't allow const to be specified with
them (otherwise .init.data sections with and without the writeable attribute
will be generated by the compiler), and since __devinitdata except for
embedded systems evaluates to <empty> unconditionally and
__cpuinitdata at least in most production kernel configurations also
likely evaluates to <empty>, it seems appropriate to add an additional
attribute allowing the respective objects to end up in .rodata rather than
.data when not used at initialization time only.

How about a slightly diffrent approach...
Consider
__cpuinitconst => function is placed in section .init.const.text
__devinitconst => function is placed in section .init.const.text

Then we in the linker scrip can distingush between the two
and locate the sections as appropriate.

This will require some updates to modpost but are align with an
idea I have had for a while.
All of the following should have dedicated sections associated
unconditionally:

__init
__cpuinit
__meminit
__initdata
__cpuinitdata
__meminitdata

And then in the linker script we decide what to do with the section.
In the built-in case we put them in the "to-be-discarded" section.
In the module case we put them as today.

The primary tasks needed to accomplish this is:
1) Update all arch linker scripts (and some of them looks ugly)
2) Teach modpost about the new sections

If you following the suggestion above this is a simple step
in this direction which would be good.

The following patch implment first step in this direction.
It is only an RFC as I have not touched anything else than
64 bit x86 for the arch specific parts.
But it should show what I tried to say above.

On top of x86.git mm-branch.

Sam

diff --git a/arch/x86/kernel/vmlinux_64.lds.S b/arch/x86/kernel/vmlinux_64.lds.S
index ba8ea97..26c1d81 100644
--- a/arch/x86/kernel/vmlinux_64.lds.S
+++ b/arch/x86/kernel/vmlinux_64.lds.S
@@ -155,12 +155,16 @@ SECTIONS
__init_begin = .;
.init.text : AT(ADDR(.init.text) - LOAD_OFFSET) {
_sinittext = .;
+ INIT_TEXT
*(.init.text)
_einittext = .;
}
- __initdata_begin = .;
- .init.data : AT(ADDR(.init.data) - LOAD_OFFSET) { *(.init.data) }
- __initdata_end = .;
+ .init.data : AT(ADDR(.init.data) - LOAD_OFFSET) {
+ __initdata_begin = .;
+ INIT_DATA
+ __initdata_end = .;
+ }
+
. = ALIGN(16);
__setup_start = .;
.init.setup : AT(ADDR(.init.setup) - LOAD_OFFSET) { *(.init.setup) }
@@ -187,8 +191,12 @@ SECTIONS
}
/* .exit.text is discard at runtime, not link time, to deal with references
from .altinstructions and .eh_frame */
- .exit.text : AT(ADDR(.exit.text) - LOAD_OFFSET) { *(.exit.text) }
- .exit.data : AT(ADDR(.exit.data) - LOAD_OFFSET) { *(.exit.data) }
+ .exit.text : AT(ADDR(.exit.text) - LOAD_OFFSET) {
+ EXIT_TEXT
+ }
+ .exit.data : AT(ADDR(.exit.data) - LOAD_OFFSET) {
+ EXIT_DATA
+ }

/* vdso blob that is mapped into user space */
vdso_start = . ;
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 9f584cc..2f359d9 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -9,10 +9,48 @@
/* Align . to a 8 byte boundary equals to maximum function alignment. */
#define ALIGN_FUNCTION() . = ALIGN(8)

+#ifdef CONFIG_HOTPLUG
+#define DEV_KEEP(sec)
+#define DEV_DISCARD(sec) *(.dev##sec)
+#else
+#define DEV_KEEP(sec) *(.dev##sec)
+#define DEV_DISCARD(sec)
+#endif
+
+#ifdef CONFIG_HOTPLUG_CPU
+#define CPU_KEEP(sec)
+#define CPU_DISCARD(sec) *(.cpu##sec)
+#else
+#define CPU_KEEP(sec) *(.cpu##sec)
+#define CPU_DISCARD(sec)
+#endif
+
+#if defined(CONFIG_MEMORY_HOTPLUG) || defined(CONFIG_ACPI_HOTPLUG_MEMORY) \
+ || defined(CONFIG_ACPI_HOTPLUG_MEMORY_MODULE)
+#define MEM_KEEP(sec)
+#define MEM_DISCARD(sec) *(.mem##sec)
+#else
+#define MEM_KEEP(sec) *(.mem##sec)
+#define MEM_DISCARD(sec)
+#endif
+
+
/* .data section */
#define DATA_DATA \
*(.data) \
*(.data.init.refok) \
+ DEV_KEEP(init.data) \
+ DEV_KEEP(init.data.const) \
+ DEV_KEEP(exit.data) \
+ DEV_KEEP(exit.data.const) \
+ CPU_KEEP(init.data) \
+ CPU_KEEP(init.data.const) \
+ CPU_KEEP(exit.data) \
+ CPU_KEEP(exit.data.const) \
+ MEM_KEEP(init.data) \
+ MEM_KEEP(init.data.const) \
+ MEM_KEEP(exit.data) \
+ MEM_KEEP(exit.data.const) \
. = ALIGN(8); \
VMLINUX_SYMBOL(__start___markers) = .; \
*(__markers) \
@@ -159,7 +197,14 @@
ALIGN_FUNCTION(); \
*(.text) \
*(.text.init.refok) \
- *(.exit.text.refok)
+ *(.exit.text.refok) \
+ DEV_KEEP(init.text) \
+ DEV_KEEP(exit.text) \
+ CPU_KEEP(init.text) \
+ CPU_KEEP(exit.text) \
+ MEM_KEEP(init.text) \
+ MEM_KEEP(exit.text)
+

/* sched.text is aling to function alignment to secure we have same
* address even at second ld pass when generating System.map */
@@ -255,6 +300,36 @@
*(.initcall7.init) \
*(.initcall7s.init)

+#define INIT_DATA \
+ *(.init.data) \
+ DEV_DISCARD(init.data) \
+ DEV_DISCARD(init.data.const) \
+ CPU_DISCARD(init.data) \
+ CPU_DISCARD(init.data.const) \
+ MEM_DISCARD(init.data) \
+ MEM_DISCARD(init.data.const)
+
+#define INIT_TEXT \
+ *(.init.text) \
+ DEV_DISCARD(init.text) \
+ CPU_DISCARD(init.text) \
+ MEM_DISCARD(init.text)
+
+#define EXIT_DATA \
+ *(.exit.data) \
+ DEV_DISCARD(exit.data) \
+ DEV_DISCARD(exit.data.const) \
+ CPU_DISCARD(exit.data) \
+ CPU_DISCARD(exit.data.const) \
+ MEM_DISCARD(exit.data) \
+ MEM_DISCARD(exit.data.const)
+
+#define EXIT_TEXT \
+ *(.exit.text) \
+ DEV_DISCARD(exit.text) \
+ CPU_DISCARD(exit.text) \
+ MEM_DISCARD(exit.text)
+
#define PERCPU(align) \
. = ALIGN(align); \
__per_cpu_start = .; \
diff --git a/include/linux/init.h b/include/linux/init.h
index 86e7e94..b72897d 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -254,42 +254,26 @@ void __init parse_early_param(void);
#define __initdata_or_module __initdata
#endif /*CONFIG_MODULES*/

-#ifdef CONFIG_HOTPLUG
-#define __devinit
-#define __devinitdata
-#define __devexit
-#define __devexitdata
-#else
-#define __devinit __init
-#define __devinitdata __initdata
-#define __devexit __exit
-#define __devexitdata __exitdata
-#endif
-
-#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_PM_CPUINIT)
-#define __cpuinit
-#define __cpuinitdata
-#define __cpuexit
-#define __cpuexitdata
-#else
-#define __cpuinit __init
-#define __cpuinitdata __initdata
-#define __cpuexit __exit
-#define __cpuexitdata __exitdata
-#endif
-
-#if defined(CONFIG_MEMORY_HOTPLUG) || defined(CONFIG_ACPI_HOTPLUG_MEMORY) \
- || defined(CONFIG_ACPI_HOTPLUG_MEMORY_MODULE)
-#define __meminit
-#define __meminitdata
-#define __memexit
-#define __memexitdata
-#else
-#define __meminit __init
-#define __meminitdata __initdata
-#define __memexit __exit
-#define __memexitdata __exitdata
-#endif
+#define __devinit __attribute__ ((__section__ (".devinit.text")))
+#define __devinitdata __attribute__ ((__section__ (".devinit.data")))
+#define __devinitcdata __attribute__ ((__section__ (".devinit.data.const")))
+#define __devexit __attribute__ ((__section__ (".devexit.text")))
+#define __devexitdata __attribute__ ((__section__ (".devexit.data")))
+#define __devexitcdata __attribute__ ((__section__ (".devexit.data.const")))
+
+#define __cpuinit __attribute__ ((__section__ (".cpuinit.text")))
+#define __cpuinitdata __attribute__ ((__section__ (".cpuinit.data")))
+#define __cpuinitcdata __attribute__ ((__section__ (".cpuinit.data.const")))
+#define __cpuexit __attribute__ ((__section__ (".cpuexit.text")))
+#define __cpuexitdata __attribute__ ((__section__ (".cpuexit.data")))
+#define __cpuexitcdata __attribute__ ((__section__ (".cpuexit.data.const")))
+
+#define __meminit __attribute__ ((__section__ (".meminit.text")))
+#define __meminitdata __attribute__ ((__section__ (".meminit.data")))
+#define __meminitcdata __attribute__ ((__section__ (".meminit.data.const")))
+#define __memexit __attribute__ ((__section__ (".memexit.text")))
+#define __memexitdata __attribute__ ((__section__ (".memexit.data")))
+#define __memexitcdata __attribute__ ((__section__ (".memexit.data.const")))

/* Functions marked as __devexit may be discarded at kernel link time, depending
on config options. Newer versions of binutils detect references from
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