With CONFIG_LTO_CLANG, we currently link modules into native
code just before modpost, which means with TRIM_UNUSED_KSYMS
enabled, we still look at the LLVM bitcode in the .o files when
generating the list of used symbols. As the bitcode doesn't
yet have calls to compiler intrinsics and llvm-nm doesn't see
function references that only exist in function-level inline
assembly, we currently need a whitelist for TRIM_UNUSED_KSYMS to
work with LTO.
This change moves module LTO linking to happen earlier, and
thus avoids the issue with LLVM bitcode and TRIM_UNUSED_KSYMS
entirely, allowing us to also drop the whitelist from
gen_autoksyms.sh.
Link: https://github.com/ClangBuiltLinux/linux/issues/1369
Signed-off-by: Sami Tolvanen <[email protected]>
---
scripts/Makefile.build | 25 ++++++++++++++++++++++++-
scripts/Makefile.lib | 7 +++++++
scripts/Makefile.modfinal | 21 ++-------------------
scripts/Makefile.modpost | 22 +++-------------------
scripts/gen_autoksyms.sh | 12 ------------
5 files changed, 36 insertions(+), 51 deletions(-)
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 10b2f2380d6f..80e0fa810870 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -202,6 +202,7 @@ sub_cmd_record_mcount = \
if [ $(@) != "scripts/mod/empty.o" ]; then \
$(objtree)/scripts/recordmcount $(RECORDMCOUNT_FLAGS) "$(@)"; \
fi;
+/
recordmcount_source := $(srctree)/scripts/recordmcount.c \
$(srctree)/scripts/recordmcount.h
else
@@ -271,12 +272,34 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) $$(objtool_dep) FORCE
$(call if_changed_rule,cc_o_c)
$(call cmd,force_checksrc)
+ifdef CONFIG_LTO_CLANG
+# 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 = \
+ $(LD) $(ld_flags) -r -o $@ \
+ $(shell [ -s $(@:.lto.o=.o.symversions) ] && \
+ echo -T $(@:.lto.o=.o.symversions)) \
+ --whole-archive $^
+
+ifdef CONFIG_STACK_VALIDATION
+# objtool was skipped for LLVM bitcode, run it now that we have compiled
+# modules into native code
+cmd_cc_lto_link_modules += ; \
+ $(objtree)/tools/objtool/objtool $(objtool_args) \
+ $(@:.ko=$(mod-prelink-ext).o)
+endif
+
+$(obj)/%.lto.o: $(obj)/%.o
+ $(call if_changed,cc_lto_link_modules)
+endif
+
cmd_mod = { \
echo $(if $($*-objs)$($*-y)$($*-m), $(addprefix $(obj)/, $($*-objs) $($*-y) $($*-m)), $(@:.mod=.o)); \
$(undefined_syms) echo; \
} > $@
-$(obj)/%.mod: $(obj)/%.o FORCE
+$(obj)/%.mod: $(obj)/%$(mod-prelink-ext).o FORCE
$(call if_changed,mod)
quiet_cmd_cc_lst_c = MKLST $@
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 10950559b223..ee985366dddf 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -225,6 +225,13 @@ dtc_cpp_flags = -Wp,-MMD,$(depfile).pre.tmp -nostdinc \
$(addprefix -I,$(DTC_INCLUDE)) \
-undef -D__DTS__
+ifeq ($(CONFIG_LTO_CLANG),y)
+# 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
+endif
+
# Objtool arguments are also needed for modfinal with LTO, so we define
# then here to avoid duplication.
objtool_args = \
diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
index 5e9b8057fb24..ff805777431c 100644
--- a/scripts/Makefile.modfinal
+++ b/scripts/Makefile.modfinal
@@ -9,7 +9,7 @@ __modfinal:
include include/config/auto.conf
include $(srctree)/scripts/Kbuild.include
-# for c_flags and objtool_args
+# for c_flags and mod-prelink-ext
include $(srctree)/scripts/Makefile.lib
# find all modules listed in modules.order
@@ -30,23 +30,6 @@ quiet_cmd_cc_o_c = CC [M] $@
ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
-ifdef CONFIG_LTO_CLANG
-# With CONFIG_LTO_CLANG, reuse the object file we compiled for modpost to
-# avoid a second slow LTO link
-prelink-ext := .lto
-
-# ELF processing was skipped earlier because we didn't have native code,
-# so let's now process the prelinked binary before we link the module.
-
-ifdef CONFIG_STACK_VALIDATION
-cmd_ld_ko_o += \
- $(objtree)/tools/objtool/objtool $(objtool_args) \
- $(@:.ko=$(prelink-ext).o);
-
-endif # CONFIG_STACK_VALIDATION
-
-endif # CONFIG_LTO_CLANG
-
quiet_cmd_ld_ko_o = LD [M] $@
cmd_ld_ko_o += \
$(LD) -r $(KBUILD_LDFLAGS) \
@@ -72,7 +55,7 @@ if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check), \
# Re-generate module BTFs if either module's .ko or vmlinux changed
-$(modules): %.ko: %$(prelink-ext).o %.mod.o scripts/module.lds $(if $(KBUILD_BUILTIN),vmlinux) FORCE
+$(modules): %.ko: %$(mod-prelink-ext).o %.mod.o scripts/module.lds $(if $(KBUILD_BUILTIN),vmlinux) FORCE
+$(call if_changed_except,ld_ko_o,vmlinux)
ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+$(if $(newer-prereqs),$(call cmd,btf_ko))
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index c383ba33d837..eef56d629799 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -41,7 +41,7 @@ __modpost:
include include/config/auto.conf
include $(srctree)/scripts/Kbuild.include
-# for ld_flags
+# for mod-prelink-ext
include $(srctree)/scripts/Makefile.lib
MODPOST = scripts/mod/modpost \
@@ -118,22 +118,6 @@ $(input-symdump):
@echo >&2 ' Modules may not have dependencies or modversions.'
@echo >&2 ' You may get many unresolved symbol warnings.'
-ifdef CONFIG_LTO_CLANG
-# With CONFIG_LTO_CLANG, .o files might be LLVM bitcode, so we need to run
-# LTO to compile them into native code before running modpost
-prelink-ext := .lto
-
-quiet_cmd_cc_lto_link_modules = LTO [M] $@
-cmd_cc_lto_link_modules = \
- $(LD) $(ld_flags) -r -o $@ \
- $(shell [ -s $(@:.lto.o=.o.symversions) ] && \
- echo -T $(@:.lto.o=.o.symversions)) \
- --whole-archive $^
-
-%.lto.o: %.o
- $(call if_changed,cc_lto_link_modules)
-endif
-
modules := $(sort $(shell cat $(MODORDER)))
# KBUILD_MODPOST_WARN can be set to avoid error out in case of undefined symbols
@@ -144,9 +128,9 @@ endif
# Read out modules.order to pass in modpost.
# Otherwise, allmodconfig would fail with "Argument list too long".
quiet_cmd_modpost = MODPOST $@
- cmd_modpost = sed 's/\.ko$$/$(prelink-ext)\.o/' $< | $(MODPOST) -T -
+ cmd_modpost = sed 's/\.ko$$/$(mod-prelink-ext)\.o/' $< | $(MODPOST) -T -
-$(output-symdump): $(MODORDER) $(input-symdump) $(modules:.ko=$(prelink-ext).o) FORCE
+$(output-symdump): $(MODORDER) $(input-symdump) $(modules:.ko=$(mod-prelink-ext).o) FORCE
$(call if_changed,modpost)
targets += $(output-symdump)
diff --git a/scripts/gen_autoksyms.sh b/scripts/gen_autoksyms.sh
index da320151e7c3..6ed0d225c8b1 100755
--- a/scripts/gen_autoksyms.sh
+++ b/scripts/gen_autoksyms.sh
@@ -26,18 +26,6 @@ if [ -n "$CONFIG_MODVERSIONS" ]; then
needed_symbols="$needed_symbols module_layout"
fi
-# With CONFIG_LTO_CLANG, LLVM bitcode has not yet been compiled into a binary
-# when the .mod files are generated, which means they don't yet contain
-# references to certain symbols that will be present in the final binaries.
-if [ -n "$CONFIG_LTO_CLANG" ]; then
- # intrinsic functions
- needed_symbols="$needed_symbols memcpy memmove memset"
- # ftrace
- needed_symbols="$needed_symbols _mcount"
- # stack protector symbols
- needed_symbols="$needed_symbols __stack_chk_fail __stack_chk_guard"
-fi
-
ksym_wl=
if [ -n "$CONFIG_UNUSED_KSYMS_WHITELIST" ]; then
# Use 'eval' to expand the whitelist path and check if it is relative
--
2.32.0.402.g57bb445576-goog
From: Sami Tolvanen <[email protected]>
Date: Fri, 16 Jul 2021 13:45:45 -0700
> With CONFIG_LTO_CLANG, we currently link modules into native
> code just before modpost, which means with TRIM_UNUSED_KSYMS
> enabled, we still look at the LLVM bitcode in the .o files when
> generating the list of used symbols. As the bitcode doesn't
> yet have calls to compiler intrinsics and llvm-nm doesn't see
> function references that only exist in function-level inline
> assembly, we currently need a whitelist for TRIM_UNUSED_KSYMS to
> work with LTO.
>
> This change moves module LTO linking to happen earlier, and
> thus avoids the issue with LLVM bitcode and TRIM_UNUSED_KSYMS
> entirely, allowing us to also drop the whitelist from
> gen_autoksyms.sh.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1369
> Signed-off-by: Sami Tolvanen <[email protected]>
> ---
> scripts/Makefile.build | 25 ++++++++++++++++++++++++-
> scripts/Makefile.lib | 7 +++++++
> scripts/Makefile.modfinal | 21 ++-------------------
> scripts/Makefile.modpost | 22 +++-------------------
> scripts/gen_autoksyms.sh | 12 ------------
> 5 files changed, 36 insertions(+), 51 deletions(-)
>
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 10b2f2380d6f..80e0fa810870 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -202,6 +202,7 @@ sub_cmd_record_mcount = \
> if [ $(@) != "scripts/mod/empty.o" ]; then \
> $(objtree)/scripts/recordmcount $(RECORDMCOUNT_FLAGS) "$(@)"; \
> fi;
> +/
Seems like a leftover or a random typo here.
> recordmcount_source := $(srctree)/scripts/recordmcount.c \
> $(srctree)/scripts/recordmcount.h
> else
> @@ -271,12 +272,34 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) $$(objtool_dep) FORCE
> $(call if_changed_rule,cc_o_c)
> $(call cmd,force_checksrc)
>
> +ifdef CONFIG_LTO_CLANG
> +# 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 = \
> + $(LD) $(ld_flags) -r -o $@ \
> + $(shell [ -s $(@:.lto.o=.o.symversions) ] && \
> + echo -T $(@:.lto.o=.o.symversions)) \
> + --whole-archive $^
> +
> +ifdef CONFIG_STACK_VALIDATION
> +# objtool was skipped for LLVM bitcode, run it now that we have compiled
> +# modules into native code
> +cmd_cc_lto_link_modules += ; \
> + $(objtree)/tools/objtool/objtool $(objtool_args) \
Now $(part-of-module) inside $(objtool_args) doesn't get expanded
properly, because previously it was being called on x.ko, and now
it's being called on x.lto.o. $(basename $@) returns "x.lto" instead
of "x", and Make doesn't find "x.lto.o" in $(real-objs-m).
An example of objtool args dump:
LTO [M] fs/btrfs/btrfs.lto.o
Call: ./tools/objtool/objtool orc generate --no-fp --no-unreachable --retpoline --uaccess fs/btrfs/btrfs.lto.o
fs/btrfs/btrfs.lto.o: warning: objtool: static_call: can't find static_call_key symbol: __SCK__might_resched
As can be seen, objtools command line no longer contains "--module".
And this warning about "can't find static_call_key" can appear only
in case of !module -> no -m|--module param was given.
As a result, modules get broken and the kernel panics after loading
initramfs.
> + $(@:.ko=$(mod-prelink-ext).o)
> +endif
> +
> +$(obj)/%.lto.o: $(obj)/%.o
> + $(call if_changed,cc_lto_link_modules)
> +endif
> +
> cmd_mod = { \
> echo $(if $($*-objs)$($*-y)$($*-m), $(addprefix $(obj)/, $($*-objs) $($*-y) $($*-m)), $(@:.mod=.o)); \
> $(undefined_syms) echo; \
> } > $@
>
> -$(obj)/%.mod: $(obj)/%.o FORCE
> +$(obj)/%.mod: $(obj)/%$(mod-prelink-ext).o FORCE
> $(call if_changed,mod)
>
> quiet_cmd_cc_lst_c = MKLST $@
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 10950559b223..ee985366dddf 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -225,6 +225,13 @@ dtc_cpp_flags = -Wp,-MMD,$(depfile).pre.tmp -nostdinc \
> $(addprefix -I,$(DTC_INCLUDE)) \
> -undef -D__DTS__
>
> +ifeq ($(CONFIG_LTO_CLANG),y)
> +# 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
> +endif
> +
> # Objtool arguments are also needed for modfinal with LTO, so we define
> # then here to avoid duplication.
> objtool_args = \
> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> index 5e9b8057fb24..ff805777431c 100644
> --- a/scripts/Makefile.modfinal
> +++ b/scripts/Makefile.modfinal
> @@ -9,7 +9,7 @@ __modfinal:
> include include/config/auto.conf
> include $(srctree)/scripts/Kbuild.include
>
> -# for c_flags and objtool_args
> +# for c_flags and mod-prelink-ext
> include $(srctree)/scripts/Makefile.lib
>
> # find all modules listed in modules.order
> @@ -30,23 +30,6 @@ quiet_cmd_cc_o_c = CC [M] $@
>
> ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
>
> -ifdef CONFIG_LTO_CLANG
> -# With CONFIG_LTO_CLANG, reuse the object file we compiled for modpost to
> -# avoid a second slow LTO link
> -prelink-ext := .lto
> -
> -# ELF processing was skipped earlier because we didn't have native code,
> -# so let's now process the prelinked binary before we link the module.
> -
> -ifdef CONFIG_STACK_VALIDATION
> -cmd_ld_ko_o += \
> - $(objtree)/tools/objtool/objtool $(objtool_args) \
> - $(@:.ko=$(prelink-ext).o);
> -
> -endif # CONFIG_STACK_VALIDATION
> -
> -endif # CONFIG_LTO_CLANG
> -
> quiet_cmd_ld_ko_o = LD [M] $@
> cmd_ld_ko_o += \
> $(LD) -r $(KBUILD_LDFLAGS) \
> @@ -72,7 +55,7 @@ if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check), \
>
>
> # Re-generate module BTFs if either module's .ko or vmlinux changed
> -$(modules): %.ko: %$(prelink-ext).o %.mod.o scripts/module.lds $(if $(KBUILD_BUILTIN),vmlinux) FORCE
> +$(modules): %.ko: %$(mod-prelink-ext).o %.mod.o scripts/module.lds $(if $(KBUILD_BUILTIN),vmlinux) FORCE
> +$(call if_changed_except,ld_ko_o,vmlinux)
> ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +$(if $(newer-prereqs),$(call cmd,btf_ko))
> diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
> index c383ba33d837..eef56d629799 100644
> --- a/scripts/Makefile.modpost
> +++ b/scripts/Makefile.modpost
> @@ -41,7 +41,7 @@ __modpost:
> include include/config/auto.conf
> include $(srctree)/scripts/Kbuild.include
>
> -# for ld_flags
> +# for mod-prelink-ext
> include $(srctree)/scripts/Makefile.lib
>
> MODPOST = scripts/mod/modpost \
> @@ -118,22 +118,6 @@ $(input-symdump):
> @echo >&2 ' Modules may not have dependencies or modversions.'
> @echo >&2 ' You may get many unresolved symbol warnings.'
>
> -ifdef CONFIG_LTO_CLANG
> -# With CONFIG_LTO_CLANG, .o files might be LLVM bitcode, so we need to run
> -# LTO to compile them into native code before running modpost
> -prelink-ext := .lto
> -
> -quiet_cmd_cc_lto_link_modules = LTO [M] $@
> -cmd_cc_lto_link_modules = \
> - $(LD) $(ld_flags) -r -o $@ \
> - $(shell [ -s $(@:.lto.o=.o.symversions) ] && \
> - echo -T $(@:.lto.o=.o.symversions)) \
> - --whole-archive $^
> -
> -%.lto.o: %.o
> - $(call if_changed,cc_lto_link_modules)
> -endif
> -
> modules := $(sort $(shell cat $(MODORDER)))
>
> # KBUILD_MODPOST_WARN can be set to avoid error out in case of undefined symbols
> @@ -144,9 +128,9 @@ endif
> # Read out modules.order to pass in modpost.
> # Otherwise, allmodconfig would fail with "Argument list too long".
> quiet_cmd_modpost = MODPOST $@
> - cmd_modpost = sed 's/\.ko$$/$(prelink-ext)\.o/' $< | $(MODPOST) -T -
> + cmd_modpost = sed 's/\.ko$$/$(mod-prelink-ext)\.o/' $< | $(MODPOST) -T -
>
> -$(output-symdump): $(MODORDER) $(input-symdump) $(modules:.ko=$(prelink-ext).o) FORCE
> +$(output-symdump): $(MODORDER) $(input-symdump) $(modules:.ko=$(mod-prelink-ext).o) FORCE
> $(call if_changed,modpost)
>
> targets += $(output-symdump)
> diff --git a/scripts/gen_autoksyms.sh b/scripts/gen_autoksyms.sh
> index da320151e7c3..6ed0d225c8b1 100755
> --- a/scripts/gen_autoksyms.sh
> +++ b/scripts/gen_autoksyms.sh
> @@ -26,18 +26,6 @@ if [ -n "$CONFIG_MODVERSIONS" ]; then
> needed_symbols="$needed_symbols module_layout"
> fi
>
> -# With CONFIG_LTO_CLANG, LLVM bitcode has not yet been compiled into a binary
> -# when the .mod files are generated, which means they don't yet contain
> -# references to certain symbols that will be present in the final binaries.
> -if [ -n "$CONFIG_LTO_CLANG" ]; then
> - # intrinsic functions
> - needed_symbols="$needed_symbols memcpy memmove memset"
> - # ftrace
> - needed_symbols="$needed_symbols _mcount"
> - # stack protector symbols
> - needed_symbols="$needed_symbols __stack_chk_fail __stack_chk_guard"
> -fi
> -
> ksym_wl=
> if [ -n "$CONFIG_UNUSED_KSYMS_WHITELIST" ]; then
> # Use 'eval' to expand the whitelist path and check if it is relative
> --
> 2.32.0.402.g57bb445576-goog
>
>
Thanks,
Al
Hi Al,
On Fri, Jul 16, 2021 at 4:00 PM Alexander Lobakin <[email protected]> wrote:
>
> From: Sami Tolvanen <[email protected]>
> Date: Fri, 16 Jul 2021 13:45:45 -0700
>
> > With CONFIG_LTO_CLANG, we currently link modules into native
> > code just before modpost, which means with TRIM_UNUSED_KSYMS
> > enabled, we still look at the LLVM bitcode in the .o files when
> > generating the list of used symbols. As the bitcode doesn't
> > yet have calls to compiler intrinsics and llvm-nm doesn't see
> > function references that only exist in function-level inline
> > assembly, we currently need a whitelist for TRIM_UNUSED_KSYMS to
> > work with LTO.
> >
> > This change moves module LTO linking to happen earlier, and
> > thus avoids the issue with LLVM bitcode and TRIM_UNUSED_KSYMS
> > entirely, allowing us to also drop the whitelist from
> > gen_autoksyms.sh.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1369
> > Signed-off-by: Sami Tolvanen <[email protected]>
> > ---
> > scripts/Makefile.build | 25 ++++++++++++++++++++++++-
> > scripts/Makefile.lib | 7 +++++++
> > scripts/Makefile.modfinal | 21 ++-------------------
> > scripts/Makefile.modpost | 22 +++-------------------
> > scripts/gen_autoksyms.sh | 12 ------------
> > 5 files changed, 36 insertions(+), 51 deletions(-)
> >
> > diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> > index 10b2f2380d6f..80e0fa810870 100644
> > --- a/scripts/Makefile.build
> > +++ b/scripts/Makefile.build
> > @@ -202,6 +202,7 @@ sub_cmd_record_mcount = \
> > if [ $(@) != "scripts/mod/empty.o" ]; then \
> > $(objtree)/scripts/recordmcount $(RECORDMCOUNT_FLAGS) "$(@)"; \
> > fi;
> > +/
>
> Seems like a leftover or a random typo here.
Oops, indeed.
> > recordmcount_source := $(srctree)/scripts/recordmcount.c \
> > $(srctree)/scripts/recordmcount.h
> > else
> > @@ -271,12 +272,34 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) $$(objtool_dep) FORCE
> > $(call if_changed_rule,cc_o_c)
> > $(call cmd,force_checksrc)
> >
> > +ifdef CONFIG_LTO_CLANG
> > +# 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 = \
> > + $(LD) $(ld_flags) -r -o $@ \
> > + $(shell [ -s $(@:.lto.o=.o.symversions) ] && \
> > + echo -T $(@:.lto.o=.o.symversions)) \
> > + --whole-archive $^
> > +
> > +ifdef CONFIG_STACK_VALIDATION
> > +# objtool was skipped for LLVM bitcode, run it now that we have compiled
> > +# modules into native code
> > +cmd_cc_lto_link_modules += ; \
> > + $(objtree)/tools/objtool/objtool $(objtool_args) \
>
> Now $(part-of-module) inside $(objtool_args) doesn't get expanded
> properly, because previously it was being called on x.ko, and now
> it's being called on x.lto.o. $(basename $@) returns "x.lto" instead
> of "x", and Make doesn't find "x.lto.o" in $(real-objs-m).
>
> An example of objtool args dump:
>
> LTO [M] fs/btrfs/btrfs.lto.o
> Call: ./tools/objtool/objtool orc generate --no-fp --no-unreachable --retpoline --uaccess fs/btrfs/btrfs.lto.o
> fs/btrfs/btrfs.lto.o: warning: objtool: static_call: can't find static_call_key symbol: __SCK__might_resched
Curiously I didn't see objtool warnings when building allmodconfig,
but you're obviously correct here. I'll fix this in v2.
> As can be seen, objtools command line no longer contains "--module".
> And this warning about "can't find static_call_key" can appear only
> in case of !module -> no -m|--module param was given.
>
> As a result, modules get broken and the kernel panics after loading
> initramfs.
Thanks for taking a look!
Sami
From: Sami Tolvanen <[email protected]>
Date: Fri, 16 Jul 2021 16:18:42 -0700
> Hi Al,
>
> On Fri, Jul 16, 2021 at 4:00 PM Alexander Lobakin <[email protected]> wrote:
> >
> > From: Sami Tolvanen <[email protected]>
> > Date: Fri, 16 Jul 2021 13:45:45 -0700
> >
> > > With CONFIG_LTO_CLANG, we currently link modules into native
> > > code just before modpost, which means with TRIM_UNUSED_KSYMS
> > > enabled, we still look at the LLVM bitcode in the .o files when
> > > generating the list of used symbols. As the bitcode doesn't
> > > yet have calls to compiler intrinsics and llvm-nm doesn't see
> > > function references that only exist in function-level inline
> > > assembly, we currently need a whitelist for TRIM_UNUSED_KSYMS to
> > > work with LTO.
> > >
> > > This change moves module LTO linking to happen earlier, and
> > > thus avoids the issue with LLVM bitcode and TRIM_UNUSED_KSYMS
> > > entirely, allowing us to also drop the whitelist from
> > > gen_autoksyms.sh.
> > >
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/1369
> > > Signed-off-by: Sami Tolvanen <[email protected]>
> > > ---
> > > scripts/Makefile.build | 25 ++++++++++++++++++++++++-
> > > scripts/Makefile.lib | 7 +++++++
> > > scripts/Makefile.modfinal | 21 ++-------------------
> > > scripts/Makefile.modpost | 22 +++-------------------
> > > scripts/gen_autoksyms.sh | 12 ------------
> > > 5 files changed, 36 insertions(+), 51 deletions(-)
> > >
> > > diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> > > index 10b2f2380d6f..80e0fa810870 100644
> > > --- a/scripts/Makefile.build
> > > +++ b/scripts/Makefile.build
> > > @@ -202,6 +202,7 @@ sub_cmd_record_mcount = \
> > > if [ $(@) != "scripts/mod/empty.o" ]; then \
> > > $(objtree)/scripts/recordmcount $(RECORDMCOUNT_FLAGS) "$(@)"; \
> > > fi;
> > > +/
> >
> > Seems like a leftover or a random typo here.
>
> Oops, indeed.
>
> > > recordmcount_source := $(srctree)/scripts/recordmcount.c \
> > > $(srctree)/scripts/recordmcount.h
> > > else
> > > @@ -271,12 +272,34 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) $$(objtool_dep) FORCE
> > > $(call if_changed_rule,cc_o_c)
> > > $(call cmd,force_checksrc)
> > >
> > > +ifdef CONFIG_LTO_CLANG
> > > +# 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 = \
> > > + $(LD) $(ld_flags) -r -o $@ \
> > > + $(shell [ -s $(@:.lto.o=.o.symversions) ] && \
> > > + echo -T $(@:.lto.o=.o.symversions)) \
> > > + --whole-archive $^
> > > +
> > > +ifdef CONFIG_STACK_VALIDATION
> > > +# objtool was skipped for LLVM bitcode, run it now that we have compiled
> > > +# modules into native code
> > > +cmd_cc_lto_link_modules += ; \
> > > + $(objtree)/tools/objtool/objtool $(objtool_args) \
> >
> > Now $(part-of-module) inside $(objtool_args) doesn't get expanded
> > properly, because previously it was being called on x.ko, and now
> > it's being called on x.lto.o. $(basename $@) returns "x.lto" instead
> > of "x", and Make doesn't find "x.lto.o" in $(real-objs-m).
To be more precise:
Previously, objtool was being called from Makefile.modfinal, where
part-of-module is hardcoded to 'y'. Now it's being called from
Makefile.build, and part-of-module is being calculated the same
way as for non-LTO build (when objtool is being called on each
object file rather than final composite object).
So, part-of-module and objtool invocation is now correct for modules
with single source file, but wrong for multi-object modules.
The simplest fix is to append '--module' to objtool args
unconditionally when we're trying to process .lto.o file.
> > An example of objtool args dump:
> >
> > LTO [M] fs/btrfs/btrfs.lto.o
> > Call: ./tools/objtool/objtool orc generate --no-fp --no-unreachable --retpoline --uaccess fs/btrfs/btrfs.lto.o
> > fs/btrfs/btrfs.lto.o: warning: objtool: static_call: can't find static_call_key symbol: __SCK__might_resched
>
> Curiously I didn't see objtool warnings when building allmodconfig,
> but you're obviously correct here. I'll fix this in v2.
>
> > As can be seen, objtools command line no longer contains "--module".
> > And this warning about "can't find static_call_key" can appear only
> > in case of !module -> no -m|--module param was given.
> >
> > As a result, modules get broken and the kernel panics after loading
> > initramfs.
>
> Thanks for taking a look!
>
> Sami
Thanks for working on ClangLTO/CFI!
Al