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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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