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>

3 files changed, 42 insertions, 2 deletions

diff --git a/Makefile b/Makefile
index 6847464402aa..8533f258c0e4 100644
--- a/Makefile
+++ b/Makefile
@@ -520,6 +520,11 @@ KBUILD_CFLAGS	+= -g
 KBUILD_AFLAGS   += -gdwarf-2
 endif
 
+# We trigger additional mismatches with less inlining
+ifdef CONFIG_DEBUG_SECTION_MISMATCH
+KBUILD_CFLAGS += $(call cc-option, -fno-inline-functions-called-once)
+endif
+
 # Force gcc to behave correct even for buggy distributions
 KBUILD_CFLAGS         += $(call cc-option, -fno-stack-protector)
 
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
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index db38ef465a63..67fb4530a6ff 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -103,6 +103,10 @@ ifneq ($(KBUILD_CHECKSRC),0)
   endif
 endif
 
+# Do section mismatch analysis for each module/built-in.o
+ifdef CONFIG_DEBUG_SECTION_MISMATCH
+  cmd_secanalysis = ; scripts/mod/modpost $@
+endif
 
 # Compile C sources (.c)
 # ---------------------------------------------------------------------------
@@ -268,7 +272,8 @@ ifdef builtin-target
 quiet_cmd_link_o_target = LD      $@
 # If the list of objects to link is empty, just create an empty built-in.o
 cmd_link_o_target = $(if $(strip $(obj-y)),\
-                      $(LD) $(ld_flags) -r -o $@ $(filter $(obj-y), $^),\
+                      $(LD) $(ld_flags) -r -o $@ $(filter $(obj-y), $^) \
+                      $(cmd_secanalysis),\
                       rm -f $@; $(AR) rcs $@)
 
 $(builtin-target): $(obj-y) FORCE
@@ -316,7 +321,7 @@ $($(subst $(obj)/,,$(@:.o=-objs)))    \
 $($(subst $(obj)/,,$(@:.o=-y)))), $^)
  
 quiet_cmd_link_multi-y = LD      $@
-cmd_link_multi-y = $(LD) $(ld_flags) -r -o $@ $(link_multi_deps)
+cmd_link_multi-y = $(LD) $(ld_flags) -r -o $@ $(link_multi_deps) $(cmd_secanalysis)
 
 quiet_cmd_link_multi-m = LD [M]  $@
 cmd_link_multi-m = $(cmd_link_multi-y)