[PATCH 4/4] x86: Add an option to compile with -ffunction-sections -fdata-sections

Tim Abbott
2009-03-24T05:30:33Z

From: Waseem Daher <wdaher@mit.edu>

This patch makes it possible to link and boot an x86 kernel with
-ffunction-sections and -fdata-sections enabled.

Modpost currently warns whenever it sees a section with a name
matching [.][0-9]+$ because they are often caused by section flag
mismatch errors. When compiling with -ffunction-sections
-fdata-sections, gcc places various classes of local symbols in
sections with names such as .rodata.__func__.12345, causing these
warnings to be printed spuriously. The simplest fix is to disable the
warning when CONFIG_FUNCTION_DATA_SECTIONS is enabled.

Signed-off-by: Waseem Daher <wdaher@mit.edu>
[tabbott@mit.edu: modpost support]
Signed-off-by: Tim Abbott <tabbott@mit.edu>
[andersk@mit.edu: depend on x86, update CONFIG_FUNCTION_TRACER conflict]
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
---
Makefile | 4 ++++
arch/x86/Kconfig | 1 +
arch/x86/kernel/vmlinux_32.lds.S | 1 +
arch/x86/kernel/vmlinux_64.lds.S | 1 +
include/asm-generic/vmlinux.lds.h | 5 ++++-
lib/Kconfig.debug | 18 ++++++++++++++++++
6 files changed, 29 insertions(+), 1 deletions(-)

diff --git a/Makefile b/Makefile
index 1ab3ebf..6fe291a 100644
--- a/Makefile
+++ b/Makefile
@@ -551,6 +551,10 @@ ifdef CONFIG_FUNCTION_TRACER
KBUILD_CFLAGS += -pg
endif

+ifdef CONFIG_FUNCTION_DATA_SECTIONS
+KBUILD_CFLAGS += -ffunction-sections -fdata-sections
+endif
+
# We trigger additional mismatches with less inlining
ifdef CONFIG_DEBUG_SECTION_MISMATCH
KBUILD_CFLAGS += $(call cc-option, -fno-inline-functions-called-once)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index bc2fbad..0af2ace 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -28,6 +28,7 @@ config X86
select HAVE_KPROBES
select ARCH_WANT_OPTIONAL_GPIOLIB
select ARCH_WANT_FRAME_POINTERS
+ select HAVE_FUNCTION_DATA_SECTIONS
select HAVE_KRETPROBES
select HAVE_FTRACE_MCOUNT_RECORD
select HAVE_DYNAMIC_FTRACE
diff --git a/arch/x86/kernel/vmlinux_32.lds.S b/arch/x86/kernel/vmlinux_32.lds.S
index 31c131a..fbc5c3f 100644
--- a/arch/x86/kernel/vmlinux_32.lds.S
+++ b/arch/x86/kernel/vmlinux_32.lds.S
@@ -194,6 +194,7 @@ SECTIONS
__bss_start = .; /* BSS */
*(.bss..page_aligned)
*(.bss)
+ *(.bss.[A-Za-z$_]*) /* handle -fdata-sections */
. = ALIGN(4);
__bss_stop = .;
_end = . ;
diff --git a/arch/x86/kernel/vmlinux_64.lds.S b/arch/x86/kernel/vmlinux_64.lds.S
index 56ed592..6e03cb2 100644
--- a/arch/x86/kernel/vmlinux_64.lds.S
+++ b/arch/x86/kernel/vmlinux_64.lds.S
@@ -223,6 +223,7 @@ SECTIONS
.bss : AT(ADDR(.bss) - LOAD_OFFSET) {
*(.bss..page_aligned)
*(.bss)
+ *(.bss.[A-Za-z$_]*) /* handle -fdata-sections */
}
__bss_stop = .;

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 0485f0b..2b31598 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -64,6 +64,7 @@
/* .data section */
#define DATA_DATA \
*(.data) \
+ *(.data.[A-Za-z$_]*) /* handle -fdata-sections */ \
*(.data..init.refok) \
*(.ref.data) \
DEV_KEEP(init.data) \
@@ -87,7 +88,8 @@
. = ALIGN((align)); \
.rodata : AT(ADDR(.rodata) - LOAD_OFFSET) { \
VMLINUX_SYMBOL(__start_rodata) = .; \
- *(.rodata) *(.rodata.*) \
+ *(.rodata) \
+ *(.rodata.[A-Za-z$_]*) /* handle -fdata-sections */ \
*(__vermagic) /* Kernel version magic */ \
*(__markers_strings) /* Markers: strings */ \
*(__tracepoints_strings)/* Tracepoints: strings */ \
@@ -254,6 +256,7 @@
ALIGN_FUNCTION(); \
*(.text.hot) \
*(.text) \
+ *(.text.[A-Za-z$_]*) /* handle -ffunction-sections */\
*(.ref.text) \
*(.text..init.refok) \
*(.text..exit.refok) \
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 1bcf9cd..d2f7427 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -591,6 +591,24 @@ config FRAME_POINTER
larger and slower, but it gives very useful debugging information
in case of kernel bugs. (precise oopses/stacktraces/warnings)

+config HAVE_FUNCTION_DATA_SECTIONS
+ bool
+
+config FUNCTION_DATA_SECTIONS
+ bool "Compile with -ffunction-sections -fdata-sections"
+ depends on HAVE_FUNCTION_DATA_SECTIONS
+ depends on !FUNCTION_TRACER
+ help
+ If you say Y here the compiler will give each function
+ and data structure its own ELF section.
+
+ This option conflicts with CONFIG_FUNCTION_TRACER, which
+ enables profiling code generation, because current GCC does
+ not support compiling with -ffunction-sections -pg (see
+ <http://gcc.gnu.org/ml/gcc-help/2008-11/msg00128.html>).
+
+ If unsure, say N.
+
config BOOT_PRINTK_DELAY
bool "Delay each boot printk message by N milliseconds"
depends on DEBUG_KERNEL && PRINTK && GENERIC_CALIBRATE_DELAY
--
1.6.2