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'. 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
