kbuild: introduce new option to enhance section mismatch analysis

Setting the option DEBUG_SECTION_MISMATCH will
report additional section mismatch'es but this
should in the end makes it possible to get rid of
all of them.

See help text in lib/Kconfig.debug for details.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

1 files changed, 30 insertions, 0 deletions

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 14fb355e3caa..748e72be6e68 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -79,6 +79,36 @@ config HEADERS_CHECK
           exported to $(INSTALL_HDR_PATH) (usually 'usr/include' in
           your build tree), to make sure they're suitable.
 
+config DEBUG_SECTION_MISMATCH
+        bool "Enable full Section mismatch analysis"
+        default n
+        help
+          The section mismatch analysis checks if there are illegal
+          references from one section to another section.
+          Linux will during link or during runtime drop some sections
+          and any use of code/data previously in these sections will
+          most likely result in an oops.
+          In the code functions and variables are annotated with
+          __init, __devinit etc. (see full list in include/linux/init.h)
+          which result in the code/data being placed in specific sections.
+          The section mismatch anaylsis are always done after a full
+          kernel build but enabling this options will in addition
+          do the following:
+          - Add the option -fno-inline-functions-called-once to gcc
+            When inlining a function annotated __init in a non-init
+            function we would loose the section information and thus
+            the analysis would not catch the illegal reference.
+            This options tell gcc to inline less but will also
+            result in a larger kernel.
+          - Run the section mismatch analysis for each module/built-in.o
+            When we run the section mismatch analysis on vmlinux.o we
+            looses valueable information about where the mismatch was
+            introduced.
+            Running the analysis for each module/built-in.o file
+            will tell where the mismatch happens much closer to the
+            source. The drawback is that we will report the same
+            mismatch at least twice.
+
 config DEBUG_KERNEL
         bool "Kernel debugging"
         help