Re: [tip: x86/core] kbuild: Fixup the IBT kbuild changes

[Masahiro Yamada <masahiroy@kernel.org>]

On Sat, Mar 19, 2022 at 12:36 AM tip-bot2 for Peter Zijlstra
<tip-bot2@linutronix.de> wrote:
>
> The following commit has been merged into the x86/core branch of tip:
>
> Commit-ID:     2f35e67f621fffc636cb802a4f93fd168cf38274
> Gitweb:        https://git.kernel.org/tip/2f35e67f621fffc636cb802a4f93fd168cf38274
> Author:        Peter Zijlstra <peterz@infradead.org>
> AuthorDate:    Fri, 18 Mar 2022 12:19:27 +01:00
> Committer:     Peter Zijlstra <peterz@infradead.org>
> CommitterDate: Fri, 18 Mar 2022 12:43:44 +01:00
>
> kbuild: Fixup the IBT kbuild changes
>
> Masahiro-san deemed my kbuild changes to support whole module objtool
> runs too terrible to live and gracefully provided an alternative.
>
> Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Link: https://lkml.kernel.org/r/CAK7LNAQ2mYMnOKMQheVi+6byUFE3KEkjm1zcndNUfe0tORGvug@mail.gmail.com


Hmm, I did not realize that
   ed53a0d971926 ("x86/alternative: Use .ibt_endbr_seal to seal indirect calls")
was already queued up.

In that commit, you introduced  *.objtool  timestamp files
(but did not  add "*.objtool" to .gitignore or "make clean" rules)

If somebody does allmodconfig tests
between the two commits,
"git status" may give a big surprise.

Let's hope nobody would do that...







> ---
>  scripts/Makefile.build | 68 ++++++++++++-----------------------------
>  scripts/Makefile.lib   |  4 +-
>  scripts/mod/modpost.c  | 12 +++----
>  3 files changed, 28 insertions(+), 56 deletions(-)
>
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 926d254..abf93d1 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -86,18 +86,12 @@ ifdef need-builtin
>  targets-for-builtin += $(obj)/built-in.a
>  endif
>
> -targets-for-modules :=
> +targets-for-modules := $(patsubst %.o, %.mod, $(filter %.o, $(obj-m)))
>
> -ifdef CONFIG_LTO_CLANG
> -targets-for-modules += $(patsubst %.o, %.lto.o, $(filter %.o, $(obj-m)))
> +ifneq ($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT),)
> +targets-for-modules += $(patsubst %.o, %.prelink.o, $(filter %.o, $(obj-m)))
>  endif
>
> -ifdef CONFIG_X86_KERNEL_IBT
> -targets-for-modules += $(patsubst %.o, %.objtool, $(filter %.o, $(obj-m)))
> -endif
> -
> -targets-for-modules += $(patsubst %.o, %.mod, $(filter %.o, $(obj-m)))
> -
>  ifdef need-modorder
>  targets-for-modules += $(obj)/modules.order
>  endif
> @@ -176,7 +170,7 @@ ifdef CONFIG_MODVERSIONS
>  #   the actual value of the checksum generated by genksyms
>  # o remove .tmp_<file>.o to <file>.o
>
> -ifdef CONFIG_LTO_CLANG
> +ifneq ($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT),)
>  # Generate .o.symversions files for each .o with exported symbols, and link these
>  # to the kernel and/or modules at the end.
>  cmd_modversions_c =                                                            \
> @@ -244,31 +238,16 @@ objtool_args =                                                            \
>         $(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)             \
>         $(if $(CONFIG_SLS), --sls)
>
> -cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool_args) $(@:.objtool=.o))
> -cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$(@:.objtool=.o): $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)
> +cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool_args) $@)
> +cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)
>
>  endif # CONFIG_STACK_VALIDATION
>
> -ifdef CONFIG_LTO_CLANG
> +ifneq ($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT),)
>
>  # Skip objtool for LLVM bitcode
>  $(obj)/%.o: objtool-enabled :=
>
> -# objtool was skipped for LLVM bitcode, run it now that we have compiled
> -# modules into native code
> -$(obj)/%.lto.o: objtool-enabled = y
> -$(obj)/%.lto.o: part-of-module := y
> -
> -else ifdef CONFIG_X86_KERNEL_IBT
> -
> -# Skip objtool on individual files
> -$(obj)/%.o: objtool-enabled :=
> -
> -# instead run objtool on the module as a whole, right before
> -# the final link pass with the linker script.
> -$(obj)/%.objtool: objtool-enabled = y
> -$(obj)/%.objtool: part-of-module := y
> -
>  else
>
>  # 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory
> @@ -310,19 +289,24 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
>         $(call if_changed_rule,cc_o_c)
>         $(call cmd,force_checksrc)
>
> -ifdef CONFIG_LTO_CLANG
> +ifneq ($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT),)
>  # Module .o files may contain LLVM bitcode, compile them into native code
>  # before ELF processing
> -quiet_cmd_cc_lto_link_modules = LTO [M] $@
> -      cmd_cc_lto_link_modules =                                                \
> +quiet_cmd_cc_prelink_modules = LD [M]  $@
> +      cmd_cc_prelink_modules =                                         \
>         $(LD) $(ld_flags) -r -o $@                                      \
> -               $(shell [ -s $(@:.lto.o=.o.symversions) ] &&            \
> -                       echo -T $(@:.lto.o=.o.symversions))             \
> +               $(shell [ -s $(@:.prelink.o=.o.symversions) ] &&                \
> +                       echo -T $(@:.prelink.o=.o.symversions))         \
>                 --whole-archive $(filter-out FORCE,$^)                  \
>                 $(cmd_objtool)
>
> -$(obj)/%.lto.o: $(obj)/%.o FORCE
> -       $(call if_changed,cc_lto_link_modules)
> +# objtool was skipped for LLVM bitcode, run it now that we have compiled
> +# modules into native code
> +$(obj)/%.prelink.o: objtool-enabled = y
> +$(obj)/%.prelink.o: part-of-module := y
> +
> +$(obj)/%.prelink.o: $(obj)/%.o FORCE
> +       $(call if_changed,cc_prelink_modules)
>  endif
>
>  cmd_mod = { \
> @@ -333,18 +317,6 @@ cmd_mod = { \
>  $(obj)/%.mod: $(obj)/%$(mod-prelink-ext).o FORCE
>         $(call if_changed,mod)
>
> -#
> -# Since objtool will re-write the file it will change the timestamps, therefore
> -# it is critical that the %.objtool file gets a timestamp *after* objtool runs.
> -#
> -# Additionally, care must be had with ordering this rule against the other rules
> -# that take %.o as a dependency.
> -#
> -cmd_objtool_mod = true $(cmd_objtool) ; touch $@
> -
> -$(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 \
> @@ -498,7 +470,7 @@ $(obj)/lib.a: $(lib-y) FORCE
>  # Do not replace $(filter %.o,^) with $(real-prereqs). When a single object
>  # module is turned into a multi object module, $^ will contain header file
>  # dependencies recorded in the .*.cmd file.
> -ifdef CONFIG_LTO_CLANG
> +ifneq ($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT),)
>  quiet_cmd_link_multi-m = AR [M]  $@
>  cmd_link_multi-m =                                             \
>         $(cmd_update_lto_symversions);                          \
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 79be57f..8bfc923 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -230,11 +230,11 @@ dtc_cpp_flags  = -Wp,-MMD,$(depfile).pre.tmp -nostdinc                    \
>                  $(addprefix -I,$(DTC_INCLUDE))                          \
>                  -undef -D__DTS__
>
> -ifeq ($(CONFIG_LTO_CLANG),y)
> +ifneq ($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT),)
>  # With CONFIG_LTO_CLANG, .o files in modules might be LLVM bitcode, so we
>  # need to run LTO to compile them into native code (.lto.o) before further
>  # processing.
> -mod-prelink-ext := .lto
> +mod-prelink-ext := .prelink
>  endif
>
>  # Useful for describing the dependency of composite objects
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 6bfa332..09c3ab0 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1989,9 +1989,9 @@ static char *remove_dot(char *s)
>                 if (m && (s[n + m] == '.' || s[n + m] == 0))
>                         s[n] = 0;
>
> -               /* strip trailing .lto */
> -               if (strends(s, ".lto"))
> -                       s[strlen(s) - 4] = '\0';
> +               /* strip trailing .prelink */
> +               if (strends(s, ".prelink"))
> +                       s[strlen(s) - 8] = '\0';
>         }
>         return s;
>  }
> @@ -2015,9 +2015,9 @@ static void read_symbols(const char *modname)
>                 /* strip trailing .o */
>                 tmp = NOFAIL(strdup(modname));
>                 tmp[strlen(tmp) - 2] = '\0';
> -               /* strip trailing .lto */
> -               if (strends(tmp, ".lto"))
> -                       tmp[strlen(tmp) - 4] = '\0';
> +               /* strip trailing .prelink */
> +               if (strends(tmp, ".prelink"))
> +                       tmp[strlen(tmp) - 8] = '\0';
>                 mod = new_module(tmp);
>                 free(tmp);
>         }



-- 
Best Regards
Masahiro Yamada