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Subject[PATCH 2/7] x86: Add an option to compile with -ffunction-sections -fdata-sections
Date
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>
---
Makefile | 4 ++++
arch/x86/kernel/vmlinux_32.lds.S | 1 +
arch/x86/kernel/vmlinux_64.lds.S | 1 +
include/asm-generic/vmlinux.lds.h | 2 ++
lib/Kconfig.debug | 9 +++++++++
scripts/Makefile.modpost | 1 +
scripts/mod/modpost.c | 10 ++++++++--
7 files changed, 26 insertions(+), 2 deletions(-)
diff --git a/Makefile b/Makefile
index 9a49960..d3d6fa4 100644
--- a/Makefile
+++ b/Makefile
@@ -540,6 +540,10 @@ 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/kernel/vmlinux_32.lds.S b/arch/x86/kernel/vmlinux_32.lds.S
index 454ab4c..c0c4323 100644
--- a/arch/x86/kernel/vmlinux_32.lds.S
+++ b/arch/x86/kernel/vmlinux_32.lds.S
@@ -193,6 +193,7 @@ SECTIONS
__bss_start = .; /* BSS */
*(.bss.kernel.page_aligned)
*(.bss)
+ *(.bss.*)
. = ALIGN(4);
__bss_stop = .;
_end = . ;
diff --git a/arch/x86/kernel/vmlinux_64.lds.S b/arch/x86/kernel/vmlinux_64.lds.S
index 6fd4547..ccb74b0 100644
--- a/arch/x86/kernel/vmlinux_64.lds.S
+++ b/arch/x86/kernel/vmlinux_64.lds.S
@@ -222,6 +222,7 @@ SECTIONS
.bss : AT(ADDR(.bss) - LOAD_OFFSET) {
*(.bss.kernel.page_aligned)
*(.bss)
+ *(.bss.*)
}
__bss_stop = .;

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index e8d1bdd..4b5aea8 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -48,6 +48,7 @@
/* .data section */
#define DATA_DATA \
*(.data) \
+ *(.data.*) \
*(.kernel.data.init.refok) \
*(.ref.data) \
DEV_KEEP(init.data) \
@@ -235,6 +236,7 @@
ALIGN_FUNCTION(); \
*(.text.hot) \
*(.text) \
+ *(.text.*) \
*(.ref.text) \
*(.kernel.text.init.refok) \
*(.kernel.text.exit.refok) \
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index b0f239e..e121ab7 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -557,6 +557,15 @@ config FRAME_POINTER
some architectures or if you use external debuggers.
If you don't debug the kernel, you can say N.

+config FUNCTION_DATA_SECTIONS
+ bool "Compile with -ffunction-sections -fdata-sections"
+ depends on !FTRACE
+ help
+ If you say Y here the compiler will give each function
+ and data structure its own ELF section.
+
+ 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
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index f4053dc..a712bb2 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -87,6 +87,7 @@ modpost = scripts/mod/modpost \
$(if $(CONFIG_DEBUG_SECTION_MISMATCH),,-S) \
$(if $(CONFIG_MARKERS),-K $(kernelmarkersfile)) \
$(if $(CONFIG_MARKERS),-M $(markersfile)) \
+ $(if $(filter -ffunction-sections -fdata-sections,$(KBUILD_CFLAGS) $(CFLAGS_KERNEL)),-F) \
$(if $(KBUILD_EXTMOD)$(KBUILD_MODPOST_WARN),-w) \
$(if $(cross_build),-c)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index afe9408..68d9e95 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -32,6 +32,8 @@ static int warn_unresolved = 0;
/* How a symbol is exported */
static int sec_mismatch_count = 0;
static int sec_mismatch_verbose = 1;
+/* Are we using CONFIG_FUNCTION_DATA_SECTIONS? */
+static int function_data_sections = 0;

enum export {
export_plain, export_unused, export_gpl,
@@ -736,7 +738,8 @@ static int check_section(const char *modname, const char *sec)
/* consume all digits */
while (*e && e != sec && isdigit(*e))
e--;
- if (*e == '.' && !strstr(sec, ".linkonce")) {
+ if (*e == '.' && !strstr(sec, ".linkonce") &&
+ !function_data_sections) {
warn("%s (%s): unexpected section name.\n"
"The (.[number]+) following section name are "
"ld generated and not expected.\n"
@@ -2063,7 +2066,7 @@ int main(int argc, char **argv)
struct ext_sym_list *extsym_iter;
struct ext_sym_list *extsym_start = NULL;

- while ((opt = getopt(argc, argv, "i:I:e:cmsSo:awM:K:")) != -1) {
+ while ((opt = getopt(argc, argv, "i:I:e:cFmsSo:awM:K:")) != -1) {
switch (opt) {
case 'i':
kernel_read = optarg;
@@ -2083,6 +2086,9 @@ int main(int argc, char **argv)
extsym_iter->file = optarg;
extsym_start = extsym_iter;
break;
+ case 'F':
+ function_data_sections = 1;
+ break;
case 'm':
modversions = 1;
break;
--
1.5.6.3


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