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Subject[PATCH] Improve vmlinux.lds.h support for arch specific linker scripts
Please review and comment..
It will be part of kbuild-next.git

Sam

commit 59d59d97e34c6593bec43666679b28da5d583958
Author: Sam Ravnborg <sam@ravnborg.org>
Date: Sun Jun 7 20:46:37 2009 +0200

Improve vmlinux.lds.h support for arch specific linker scripts

To support alingment of the individual architecture specific linker scripts
provide a set of general definitions in vmlinux.lds.h

With these definitions applied the diverse linekr scripts can be reduced
in line count and their readability are improved - IMO.

A sample linker script is included to give the preferred
order of the sections for the architectures that do not
have any special requirments.

These definitions are also a first step towards eventual
support for -ffunction-sections.
The definitions makes it much easier to do a global
renaming of section names - but the main purpose is
to clean up the linker scripts.

Tim Aboot has provided a lot of inputs to improve
the definitions - all faults are mine.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Tim Abbott <tabbott@mit.edu>

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 3edb114..d61058e 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -1,4 +1,58 @@
-#include <linux/section-names.h>
+/*
+ * Helper macros to support writing architecture specific
+ * linker scripts.
+ *
+ * A minimal linker scripts has following content:
+ * [This is a sample, architectures may have special requiriements]
+ *
+ * OUTPUT_FORMAT(...)
+ * OUTPUT_ARCH(...)
+ * ENTRY(...)
+ * SECTIONS
+ * {
+ * . = START;
+ * __init_begin = .;
+ * HEAD_SECTION
+ * INIT_TEXT_SECTION(PAGE_SIZE)
+ * INIT_DATA_SECTION(...)
+ * PERCPU(PAGE_SIZE)
+ * __init_end = .;
+ *
+ * _stext = .;
+ * TEXT_SECTION = 0
+ * _etext = .;
+ *
+ * _sdata = .;
+ * RO_DATA_SECTION(PAGE_SIZE)
+ * RW_DATA_SECTION(...)
+ * _edata = .;
+ *
+ * EXCEPTION_TABLE(...)
+ * NOTES
+ *
+ * __bss_start = .;
+ * BSS_SECTION(0, 0)
+ * __bss_stop = .;
+ * _end = .;
+ *
+ * /DISCARD/ : {
+ * EXIT_TEXT
+ * EXIT_DATA
+ * *(.exitcall.exit)
+ * }
+ * STABS_DEBUG
+ * DWARF_DEBUG
+ * }
+ *
+ * [__init_begin, __init_end] is the init section that may be freed after init
+ * [_stext, _etext] is the text section
+ * [_sdata, _edata] is the data section
+ *
+ * Some of the included output section have their own set of constants.
+ * Examples are: [__initramfs_start, __initramfs_end] for initramfs and
+ * [__nosave_begin, __nosave_end] for the nosave data
+ */
+ #include <linux/section-names.h>

#ifndef LOAD_OFFSET
#define LOAD_OFFSET 0
@@ -116,7 +170,36 @@
FTRACE_EVENTS() \
TRACE_SYSCALLS()

-#define RO_DATA(align) \
+/*
+ * Data section helpers
+ */
+#define NOSAVE_DATA \
+ . = ALIGN(PAGE_SIZE); \
+ VMLINUX_SYMBOL(__nosave_begin) = .; \
+ *(.data.nosave) \
+ . = ALIGN(PAGE_SIZE); \
+ VMLINUX_SYMBOL(__nosave_end) = .;
+
+#define PAGE_ALIGNED_DATA(page_align) \
+ . = ALIGN(page_align); \
+ *(.data.page_aligned)
+
+#define READ_MOSTLY_DATA(align) \
+ . = ALIGN(align); \
+ *(.data.read_mostly)
+
+#define CACHELINE_ALIGNED_DATA(align) \
+ . = ALIGN(align); \
+ *(.data.cacheline_aligned)
+
+#define INIT_TASK(align) \
+ . = ALIGN(align); \
+ *(.data.init_task)
+
+/*
+ * Read only Data
+ */
+#define RO_DATA_SECTION(align) \
. = ALIGN((align)); \
.rodata : AT(ADDR(.rodata) - LOAD_OFFSET) { \
VMLINUX_SYMBOL(__start_rodata) = .; \
@@ -270,9 +353,10 @@
} \
. = ALIGN((align));

-/* RODATA provided for backward compatibility.
+/* RODATA & RO_DATA provided for backward compatibility.
* All archs are supposed to use RO_DATA() */
-#define RODATA RO_DATA(4096)
+#define RODATA RO_DATA_SECTION(4096)
+#define RO_DATA(align) RO_DATA_SECTION(align)

#define SECURITY_INIT \
.security_initcall.init : AT(ADDR(.security_initcall.init) - LOAD_OFFSET) { \
@@ -332,6 +416,31 @@
/* Section used for early init (in .S files) */
#define HEAD_TEXT *(HEAD_TEXT_SECTION)

+#define HEAD_SECTION \
+ .head.text : AT(ADDR(.head.text) - LOAD_OFFSET) { \
+ HEAD_TEXT
+ }
+
+/*
+ * Exception table
+ */
+#define EXCEPTION_TABLE(align) \
+ . = ALIGN(align); \
+ __ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) { \
+ VMLINUX_SYMBOL(__start___ex_table) = .; \
+ *(__ex_table) \
+ VMLINUX_SYMBOL(__stop___ex_table) = .; \
+ }
+
+/*
+ * Init task
+ */
+#define INIT_TASK_DATA(align) \
+ . = ALIGN(align); \
+ .data.init_task : { \
+ INIT_TASK \
+ }
+
/* init and exit section handling */
#define INIT_DATA \
*(.init.data) \
@@ -364,9 +473,32 @@
CPU_DISCARD(exit.text) \
MEM_DISCARD(exit.text)

- /* DWARF debug sections.
- Symbols in the DWARF debugging sections are relative to
- the beginning of the section so we begin them at 0. */
+/*
+ * bss (Block Started by Symbol) - uninitialized data
+ * zeroed during startup
+ */
+#define SBSS \
+ .sbss : AT(ADDR(.sbss) - LOAD_OFFSET) { \
+ *(.sbss) \
+ *(.scommon) \
+ }
+
+#define BSS(bss_align) \
+ . = ALIGN(bss_align); \
+ .bss : AT(ADDR(.bss) - LOAD_OFFSET) { \
+ VMLINUX_SYMBOL(__bss_start) = .; \
+ *(.bss.page_aligned) \
+ *(.dynbss) \
+ *(.bss) \
+ *(COMMON) \
+ VMLINUX_SYMBOL(__bss_stop) = .; \
+ }
+
+/*
+ * DWARF debug sections.
+ * Symbols in the DWARF debugging sections are relative to
+ * the beginning of the section so we begin them at 0.
+ */
#define DWARF_DEBUG \
/* DWARF 1 */ \
.debug 0 : { *(.debug) } \
@@ -433,6 +565,12 @@
VMLINUX_SYMBOL(__stop_notes) = .; \
}

+#define INIT_SETUP(initsetup_align) \
+ . = ALIGN(initsetup_align); \
+ VMLINUX_SYMBOL(__setup_start) = .; \
+ *(.init.setup) \
+ VMLINUX_SYMBOL(__setup_end) = .;
+
#define INITCALLS \
*(.initcallearly.init) \
VMLINUX_SYMBOL(__early_initcall_end) = .; \
@@ -454,6 +592,31 @@
*(.initcall7.init) \
*(.initcall7s.init)

+#define INIT_CALLS \
+ VMLINUX_SYMBOL(__initcall_start) = .; \
+ INITCALLS \
+ VMLINUX_SYMBOL(__initcall_end) = .;
+
+#define CON_INITCALL \
+ VMLINUX_SYMBOL(__con_initcall_start) = .; \
+ *(.con_initcall.init) \
+ VMLINUX_SYMBOL(__con_initcall_end) = .;
+
+#define SECURITY_INITCALL \
+ VMLINUX_SYMBOL(__security_initcall_start) = .; \
+ *(.security_initcall.init) \
+ VMLINUX_SYMBOL(__security_initcall_end) = .;
+
+#ifdef CONFIG_BLK_DEV_INITRD
+#define INIT_RAM_FS \
+ . = ALIGN(PAGE_SIZE); \
+ VMLINUX_SYMBOL(__initramfs_start) = .; \
+ *(.init.ramfs) \
+ VMLINUX_SYMBOL(__initramfs_end) = .;
+#else
+#define INITRAMFS
+#endif
+
/**
* PERCPU_VADDR - define output section for percpu area
* @vaddr: explicit base address (optional)
@@ -510,3 +673,57 @@
*(.data.percpu.shared_aligned) \
VMLINUX_SYMBOL(__per_cpu_end) = .; \
}
+
+
+/*
+ * Definition of the high level *_SECTION macros
+ * They will fit only a subset of the architectures
+ */
+
+
+/*
+ * Writeable data.
+ * All sections are combined in a single .data section.
+ * The sections following CONSTRUCTORS are arranged so their
+ * typical alignment matches.
+ * A cacheline is typical/always less than a PAGE_SIZE so
+ * the sections that has this restriction (or similar)
+ * is located before the ones requiring PAGE_SIZE alignment.
+ * NOSAVE_DATA starts and ends with a PAGE_SIZE alignment which
+ * matches the requirment of PAGE_ALIGNED_DATA.
+ *
+/* use 0 as page_align if page_aligned data is not used */
+#define RW_DATA_SECTION(cacheline, nosave, pagealigned, inittask) \
+ . = ALIGN(PAGE_SIZE); \
+ .data : AT(ADDR(.data) - LOAD_OFFSET) { \
+ INIT_TASK(inittask) \
+ CACHELINE_ALIGNED_DATA(cacheline) \
+ READ_MOSTLY_DATA(cacheline) \
+ DATA_DATA \
+ CONSTRUCTORS \
+ NOSAVE_DATA(nosave) \
+ PAGE_ALIGNED_DATA(pagealigned) \
+ }
+
+#define INIT_TEXT_SECTION(inittext_align) \
+ . = ALIGN(inittext_align); \
+ .init.text : AT(ADDR(.init.text) - LOAD_OFFSET) { \
+ VMLINUX_SYMBOL(_sinittext) = .; \
+ INIT_TEXT \
+ VMLINUX_SYMBOL(_einittext) = .; \
+ }
+
+#define INIT_DATA_SECTION(initsetup_align) \
+ .init.data : AT(ADDR(.init.data) - LOAD_OFFSET) { \
+ INIT_DATA \
+ INIT_SETUP(initsetup_align) \
+ INIT_CALLS \
+ CON_INITCALL \
+ SECURITY_INITCALL \
+ INIT_RAM_FS \
+ }
+
+#define BSS_SECTION(sbss_align, bss_align) \
+ SBSS \
+ BSS(bss_align) \
+ . = ALIGN(4); \

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