genksyms: track symbol checksum changes

Sometimes it is preferable to avoid changes of exported symbol checksums
(to avoid breaking externally provided modules).  When a checksum change
occurs, it can be hard to figure out what caused this change: underlying
types may have changed, or additional type information may simply have
become available at the point where a symbol is exported.

Add a new --reference option to genksyms which allows it to report why
checksums change, based on the type information dumps it creates with the
--dump-types flag.  Genksyms will read in such a dump from a previous run,
and report which symbols have changed (and why).

The behavior can be controlled for an entire build as follows: If
KBUILD_SYMTYPES is set, genksyms uses --dump-types to produce *.symtypes
dump files.  If any *.symref files exist, those will be used as the
reference to check against.  If KBUILD_PRESERVE is set, checksum changes
will fail the build.

Signed-off-by: Andreas Gruenbacher <agruen@suse.de>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

1 files changed, 13 insertions, 3 deletions

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 468fbc9016c..d21f0eac2e5 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -153,12 +153,18 @@ $(obj)/%.i: $(src)/%.c FORCE
 
 quiet_cmd_cc_symtypes_c = SYM $(quiet_modtag) $@
 cmd_cc_symtypes_c          = \
+                set -e;                                                 \
                 $(CPP) -D__GENKSYMS__ $(c_flags) $<                     \
-                | $(GENKSYMS) -T $@ >/dev/null;                         \
+                | $(GENKSYMS) -T $@                                     \
+                              -r $(firstword $(wildcard                 \
+                                     $(@:.symtypes=.symref) /dev/null)) \
+                              $(if $(KBUILD_PRESERVE),-p)               \
+                              -a $(ARCH)                                \
+                  >/dev/null;                                           \
                 test -s $@ || rm -f $@
 
 $(obj)/%.symtypes : $(src)/%.c FORCE
-        $(call if_changed_dep,cc_symtypes_c)
+        $(call cmd,cc_symtypes_c)
 
 # C (.c) files
 # The C file is compiled and updated dependency information is generated.
@@ -187,7 +193,11 @@ cmd_modversions =							\
         if $(OBJDUMP) -h $(@D)/.tmp_$(@F) | grep -q __ksymtab; then     \
                 $(CPP) -D__GENKSYMS__ $(c_flags) $<                     \
                 | $(GENKSYMS) $(if $(KBUILD_SYMTYPES),                  \
-                              -T $(@D)/$(@F:.o=.symtypes)) -a $(ARCH)   \
+                                   -T $(@:.o=.symtypes))                \
+                              -r $(firstword $(wildcard                 \
+                                     $(@:.o=.symref) /dev/null))        \
+                              $(if $(KBUILD_PRESERVE),-p)               \
+                              -a $(ARCH)                                \
                 > $(@D)/.tmp_$(@F:.o=.ver);                             \
                                                                         \
                 $(LD) $(LDFLAGS) -r -o $@ $(@D)/.tmp_$(@F)              \