Hello Masahiro, On Wed, 2 Nov 2022 at 10:13, Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > This is an experimental patch, driven by the feedback from Jiri Slaby > and Michael Matz. [1] > > Michael Matz says: > "I know of no linker (outside LTO-like modes) that processes > archives in a different order than first-to-last-member (under > whole-archive), but that's not guaranteed anywhere. So relying on > member-order within archives is always brittle." > > It is pretty easy to pass the list of objects instead of a thin archive > because the linker supports the '@file' syntax, where command line > arguments are read from 'file'. > Can you explain which problem is solved by doing this? If we can only produce a working kernel if each object is linked in the order it appears in the archive, I think we have bigger problems that need solving regardless. And for the .head.text objects that need to appear at the start of the binary image, I think the reported issue with __head annotated C functions on x86 needs to be addressed by getting rid of __head entirely (which seems to have been introduced without proper justification) > Without this patch, the linker receives > > --whole-archive vmlinux.a --no-whole-archive > > With this patch, the linker will receive > > @vmlinux.order > > Here, vmlinux.order is a text file that lists built-in objects in the > correct link order. > > I am not a toolchain expert. I just want to know if this makes any > difference from the linker perspective and from (non-upstreamed) GCC-LTO > perspective. > > (I know this patch does not work for Clang LTO because I did not touch > scripts/generate_initcall_order.pl) > > This patch may be unneeded because more correct patches were submitted [2] > but I am still curious about "thin archive vs direct object list". > > [1]: https://lore.kernel.org/linux-kbuild/alpine.LSU.2.20.2210251210140.29399@xxxxxxxxxxxxx/ > [2]: https://lore.kernel.org/all/20221101161529.1634188-1-alexandr.lobakin@xxxxxxxxx/ > > Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> > --- > > Makefile | 21 ++++++++++----------- > scripts/Makefile.modpost | 5 +++-- > scripts/Makefile.vmlinux_o | 6 +++--- > scripts/clang-tools/gen_compile_commands.py | 21 ++++++++++++++++++++- > scripts/link-vmlinux.sh | 8 ++++---- > 5 files changed, 40 insertions(+), 21 deletions(-) > > diff --git a/Makefile b/Makefile > index e9e7eff906a5..511484a3dacb 100644 > --- a/Makefile > +++ b/Makefile > @@ -1213,19 +1213,18 @@ quiet_cmd_autoksyms_h = GEN $@ > $(autoksyms_h): > $(call cmd,autoksyms_h) > > -# '$(AR) mPi' needs 'T' to workaround the bug of llvm-ar <= 14 > -quiet_cmd_ar_vmlinux.a = AR $@ > - cmd_ar_vmlinux.a = \ > - rm -f $@; \ > - $(AR) cDPrST $@ $(KBUILD_VMLINUX_OBJS); \ > - $(AR) mPiT $$($(AR) t $@ | sed -n 1p) $@ $$($(AR) t $@ | grep -F -f $(srctree)/scripts/head-object-list.txt) > +quiet_cmd_vmlinux_order = GEN $@ > + cmd_vmlinux_order = \ > + { $(foreach m, $(KBUILD_VMLINUX_OBJS), $(AR) t $m;) :; } > $(tmp-target) ; \ > + grep -F -f $(srctree)/scripts/head-object-list.txt $(tmp-target) > $@; \ > + grep -F -f $(srctree)/scripts/head-object-list.txt $(tmp-target) -v >> $@ > > -targets += vmlinux.a > -vmlinux.a: $(KBUILD_VMLINUX_OBJS) scripts/head-object-list.txt autoksyms_recursive FORCE > - $(call if_changed,ar_vmlinux.a) > +targets += vmlinux.order > +vmlinux.order: $(KBUILD_VMLINUX_OBJS) scripts/head-object-list.txt autoksyms_recursive FORCE > + $(call if_changed,vmlinux_order) > > PHONY += vmlinux_o > -vmlinux_o: vmlinux.a $(KBUILD_VMLINUX_LIBS) > +vmlinux_o: vmlinux.order $(KBUILD_VMLINUX_LIBS) > $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.vmlinux_o > > vmlinux.o modules.builtin.modinfo modules.builtin: vmlinux_o > @@ -2037,7 +2036,7 @@ quiet_cmd_gen_compile_commands = GEN $@ > cmd_gen_compile_commands = $(PYTHON3) $< -a $(AR) -o $@ $(filter-out $<, $(real-prereqs)) > > $(extmod_prefix)compile_commands.json: scripts/clang-tools/gen_compile_commands.py \ > - $(if $(KBUILD_EXTMOD),, vmlinux.a $(KBUILD_VMLINUX_LIBS)) \ > + $(if $(KBUILD_EXTMOD),, vmlinux.order $(KBUILD_VMLINUX_LIBS)) \ > $(if $(CONFIG_MODULES), $(MODORDER)) FORCE > $(call if_changed,gen_compile_commands) > > diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost > index e41dee64d429..1d6847da39bd 100644 > --- a/scripts/Makefile.modpost > +++ b/scripts/Makefile.modpost > @@ -70,12 +70,13 @@ quiet_cmd_vmlinux_objs = GEN $@ > for f in $(real-prereqs); do \ > case $${f} in \ > *libgcc.a) ;; \ > - *) $(AR) t $${f} ;; \ > + *.a) $(AR) t $${f} ;; \ > + *) cat $${f} ;; \ > esac \ > done > $@ > > targets += .vmlinux.objs > -.vmlinux.objs: vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE > +.vmlinux.objs: vmlinux.order $(KBUILD_VMLINUX_LIBS) FORCE > $(call if_changed,vmlinux_objs) > > vmlinux.o-if-present := $(wildcard vmlinux.o) > diff --git a/scripts/Makefile.vmlinux_o b/scripts/Makefile.vmlinux_o > index 0edfdb40364b..6eb07f2bb39f 100644 > --- a/scripts/Makefile.vmlinux_o > +++ b/scripts/Makefile.vmlinux_o > @@ -18,7 +18,7 @@ quiet_cmd_gen_initcalls_lds = GEN $@ > $(PERL) $(real-prereqs) > $@ > > .tmp_initcalls.lds: $(srctree)/scripts/generate_initcall_order.pl \ > - vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE > + vmlinux.order $(KBUILD_VMLINUX_LIBS) FORCE > $(call if_changed,gen_initcalls_lds) > > targets := .tmp_initcalls.lds > @@ -48,7 +48,7 @@ quiet_cmd_ld_vmlinux.o = LD $@ > cmd_ld_vmlinux.o = \ > $(LD) ${KBUILD_LDFLAGS} -r -o $@ \ > $(addprefix -T , $(initcalls-lds)) \ > - --whole-archive vmlinux.a --no-whole-archive \ > + @vmlinux.order \ > --start-group $(KBUILD_VMLINUX_LIBS) --end-group \ > $(cmd_objtool) > > @@ -57,7 +57,7 @@ define rule_ld_vmlinux.o > $(call cmd,gen_objtooldep) > endef > > -vmlinux.o: $(initcalls-lds) vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE > +vmlinux.o: $(initcalls-lds) vmlinux.order $(KBUILD_VMLINUX_LIBS) FORCE > $(call if_changed_rule,ld_vmlinux.o) > > targets += vmlinux.o > diff --git a/scripts/clang-tools/gen_compile_commands.py b/scripts/clang-tools/gen_compile_commands.py > index d800b2c0af97..c8ba9f084bd0 100755 > --- a/scripts/clang-tools/gen_compile_commands.py > +++ b/scripts/clang-tools/gen_compile_commands.py > @@ -57,7 +57,7 @@ def parse_arguments(): > parser.add_argument('-a', '--ar', type=str, default='llvm-ar', help=ar_help) > > paths_help = ('directories to search or files to parse ' > - '(files should be *.o, *.a, or modules.order). ' > + '(files should be *.o, *.a, or *.order). ' > 'If nothing is specified, the current directory is searched') > parser.add_argument('paths', type=str, nargs='*', help=paths_help) > > @@ -124,6 +124,23 @@ def cmdfiles_for_a(archive, ar): > yield to_cmdfile(obj) > > > +def cmdfiles_for_vmlinux_order(vmlinux_order): > + """Generate the iterator of .cmd files associated with the vmlinux.order. > + > + Parse the given vmlinux.order, and yield every .cmd file used to build the > + contained modules. > + > + Args: > + vmlinux_order: The vmlinux.order file to parse > + > + Yields: > + The path to every .cmd file found > + """ > + with open(vmlinux_order) as f: > + for line in f: > + yield to_cmdfile(line.rstrip()) > + > + > def cmdfiles_for_modorder(modorder): > """Generate the iterator of .cmd files associated with the modules.order. > > @@ -203,6 +220,8 @@ def main(): > cmdfiles = cmdfiles_in_dir(path) > elif path.endswith('.a'): > cmdfiles = cmdfiles_for_a(path, ar) > + elif path.endswith('vmlinux.order'): > + cmdfiles = cmdfiles_for_vmlinux_order(path) > elif path.endswith('modules.order'): > cmdfiles = cmdfiles_for_modorder(path) > else: > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh > index 918470d768e9..617ed443e377 100755 > --- a/scripts/link-vmlinux.sh > +++ b/scripts/link-vmlinux.sh > @@ -3,15 +3,15 @@ > # > # link vmlinux > # > -# vmlinux is linked from the objects in vmlinux.a and $(KBUILD_VMLINUX_LIBS). > -# vmlinux.a contains objects that are linked unconditionally. > +# vmlinux is linked from the objects in vmlinux.order and $(KBUILD_VMLINUX_LIBS). > +# vmlinux.order is a text file that contains objects that are linked unconditionally. > # $(KBUILD_VMLINUX_LIBS) are archives which are linked conditionally > # (not within --whole-archive), and do not require symbol indexes added. > # > # vmlinux > # ^ > # | > -# +--< vmlinux.a > +# +--< vmlinux.order > # | > # +--< $(KBUILD_VMLINUX_LIBS) > # | +--< lib/lib.a + more > @@ -65,7 +65,7 @@ vmlinux_link() > objs=vmlinux.o > libs= > else > - objs=vmlinux.a > + objs=@vmlinux.order > libs="${KBUILD_VMLINUX_LIBS}" > fi > > -- > 2.34.1 >
