Re: [PATCH v4 00/45] x86: Kernel IBT

[Peter Zijlstra]

On Sun, Mar 13, 2022 at 09:52:14AM +0100, Peter Zijlstra wrote:
> On Sat, Mar 12, 2022 at 05:33:39PM -0800, Alexei Starovoitov wrote:
> > During the build with gcc 8.5 I see:
> > 
> > arch/x86/crypto/crc32c-intel.o: warning: objtool: file already has
> > .ibt_endbr_seal, skipping
> > arch/x86/crypto/crc32c-intel.o: warning: objtool: file already has
> > .orc_unwind section, skipping
> >   LD [M]  crypto/async_tx/async_xor.ko
> >   LD [M]  crypto/authenc.ko
> > make[3]: *** [../scripts/Makefile.modfinal:61:
> > arch/x86/crypto/crc32c-intel.ko] Error 255
> > make[3]: *** Waiting for unfinished jobs....
> > 
> > but make clean cures it.
> > I suspect it's some missing makefile dependency.
> 
> Yes, I recently ran into it; I've been trying to kick Makefile into
> submission but have not had success yet. Will try again on Monday.
> 
> Problem appears to be that it will re-link .ko even though .o hasn't
> changed, resulting in duplicate objtool runs. I've been trying to have
> makefile generate .o.objtool empty file to serve as dependency marker to
> avoid doing second objtool run, but like said, no luck yet.

Masahiro-san, I'm trying the below, but afaict it's not working because
the rule for the .o file itself:

$(multi-obj-m): FORCE
	$(call if_changed,link_multi-m)

will in fact update the timestamp of the .o file, even if if_changed
nops out the cmd. Concequently all rules that try to use if_changed with
this .o file as a dependency will find it newer and run anyway.


remake -x output of a fs/f2fs/ module (re)build:

     Prerequisite 'FORCE' of target 'fs/f2fs/f2fs.o' does not exist.
    Must remake target 'fs/f2fs/f2fs.o'.
../scripts/Makefile.build:454: target 'fs/f2fs/f2fs.o' does not exist
##>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
:
##<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
    Successfully remade target file 'fs/f2fs/f2fs.o'.
   Prerequisite 'fs/f2fs/f2fs.o' is newer than target 'fs/f2fs/f2fs.mod'.
   Prerequisite 'FORCE' of target 'fs/f2fs/f2fs.mod' does not exist.
  Must remake target 'fs/f2fs/f2fs.mod'.
../scripts/Makefile.build:281: update target 'fs/f2fs/f2fs.mod' due to: fs/f2fs/f2fs.o
##>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
set -e;   { echo  fs/f2fs/dir.o fs/f2fs/file.o fs/f2fs/inode.o fs/f2fs/namei.o fs/f2fs/hash.o fs/f2fs/super.o fs/f2fs/inline.o fs/f2fs/checkpoint.o fs/f2fs/gc.o fs/f2fs/data.o fs/f2fs/node.o fs/f2fs/segment.o fs/f2fs/recovery.o fs/f2fs/shrinker.o fs/f2fs/extent_cache.o fs/f2fs/sysfs.o fs/f2fs/debug.o fs/f2fs/xattr.o fs/f2fs/acl.o fs/f2fs/iostat.o;  echo; } > fs/f2fs/f2fs.mod; printf '%s\n' 'cmd_fs/f2fs/f2fs.mod := { echo  fs/f2fs/dir.o fs/f2fs/file.o fs/f2fs/inode.o fs/f2fs/namei.o fs/f2fs/hash.o fs/f2fs/super.o fs/f2fs/inline.o fs/f2fs/checkpoint.o fs/f2fs/gc.o fs/f2fs/data.o fs/f2fs/node.o fs/f2fs/segment.o fs/f2fs/recovery.o fs/f2fs/shrinker.o fs/f2fs/extent_cache.o fs/f2fs/sysfs.o fs/f2fs/debug.o fs/f2fs/xattr.o fs/f2fs/acl.o fs/f2fs/iostat.o;  echo; } > fs/f2fs/f2fs.mod' > fs/f2fs/.f2fs.mod.cmd
##<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
  Successfully remade target file 'fs/f2fs/f2fs.mod'.
   Prerequisite 'fs/f2fs/f2fs.o' is newer than target 'fs/f2fs/f2fs.objtool'.
   Prerequisite 'FORCE' of target 'fs/f2fs/f2fs.objtool' does not exist.
  Must remake target 'fs/f2fs/f2fs.objtool'.
../scripts/Makefile.build:287: update target 'fs/f2fs/f2fs.objtool' due to: fs/f2fs/f2fs.o
##>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
set -e;   { echo fs/f2fs/f2fs.o  ; ./tools/objtool/objtool orc generate  --module  --lto --ibt  --no-fp    --uaccess   fs/f2fs/f2fs.o ; } > fs/f2fs/f2fs.objtool; printf '%s\n' 'cmd_fs/f2fs/f2fs.objtool := { echo fs/f2fs/f2fs.o  ; ./tools/objtool/objtool orc generate  --module  --lto --ibt  --no-fp    --uaccess   fs/f2fs/f2fs.o ; } > fs/f2fs/f2fs.objtool' > fs/f2fs/.f2fs.objtool.cmd
##<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
fs/f2fs/f2fs.o: warning: objtool: file already has .static_call_sites section, skipping
fs/f2fs/f2fs.o: warning: objtool: file already has .ibt_endbr_seal, skipping
fs/f2fs/f2fs.o: warning: objtool: file already has .orc_unwind section, skipping
../scripts/Makefile.build:286: *** [fs/f2fs/f2fs.objtool] error 255


Where we can see that we don't re-generate f2fs.o (empty command), but
then we do re-generate f2fs.mod because f2fs.o is newer and the same
happens for the new f2fs.objtool.

Help?

---
Index: linux-2.6/scripts/Makefile.build
===================================================================
--- linux-2.6.orig/scripts/Makefile.build
+++ linux-2.6/scripts/Makefile.build
@@ -92,6 +92,10 @@ ifdef CONFIG_LTO_CLANG
 targets-for-modules += $(patsubst %.o, %.lto.o, $(filter %.o, $(obj-m)))
 endif
 
+ifdef CONFIG_X86_KERNEL_IBT
+targets-for-modules += $(patsubst %.o, %.objtool, $(filter %.o, $(obj-m)))
+endif
+
 ifdef need-modorder
 targets-for-modules += $(obj)/modules.order
 endif
@@ -276,6 +280,12 @@ cmd_mod = { \
 $(obj)/%.mod: $(obj)/%$(mod-prelink-ext).o FORCE
 	$(call if_changed,mod)
 
+cmd_objtool_mod =							\
+	{ echo $< $(cmd_objtool) ; } > $@
+
+$(obj)/%.objtool: $(obj)/%$(mod-prelink-ext).o FORCE
+	$(call if_changed,objtool_mod)
+
 quiet_cmd_cc_lst_c = MKLST   $@
       cmd_cc_lst_c = $(CC) $(c_flags) -g -c -o $*.o $< && \
 		     $(CONFIG_SHELL) $(srctree)/scripts/makelst $*.o \
Index: linux-2.6/scripts/Makefile.lib
===================================================================
--- linux-2.6.orig/scripts/Makefile.lib
+++ linux-2.6/scripts/Makefile.lib
@@ -552,9 +552,8 @@ objtool_args =								\
 	$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)		\
 	$(if $(CONFIG_SLS), --sls)
 
-cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool_args) $@)
-cmd_objtool_mod = $(if $(objtool-enabled), $(objtool) $(objtool_args) $(@:.ko=.o) ; )
-cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)
+cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool_args) $(@:.objtool=.o))
+cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$(@:.objtool=.o): $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)
 
 endif # CONFIG_STACK_VALIDATION
 
@@ -575,8 +574,8 @@ $(obj)/%.o: objtool-enabled :=
 
 # instead run objtool on the module as a whole, right before
 # the final link pass with the linker script.
-%.ko: objtool-enabled = y
-%.ko: part-of-module := y
+$(obj)/%.objtool: objtool-enabled = y
+$(obj)/%.objtool: part-of-module := y
 
 else
 
Index: linux-2.6/scripts/Makefile.modfinal
===================================================================
--- linux-2.6.orig/scripts/Makefile.modfinal
+++ linux-2.6/scripts/Makefile.modfinal
@@ -32,7 +32,6 @@ ARCH_POSTLINK := $(wildcard $(srctree)/a
 
 quiet_cmd_ld_ko_o = LD [M]  $@
       cmd_ld_ko_o +=							\
-	$(cmd_objtool_mod)						\
 	$(LD) -r $(KBUILD_LDFLAGS)					\
 		$(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE)		\
 		-T scripts/module.lds -o $@ $(filter %.o, $^);		\