[PATCH 1/2] kbuild: remove incremental linking option

Nicholas Piggin
2018-02-10T14:25:19Z

This removes the old `ld -r` incremental link option, which has not
been selected by any architecture since June 2017.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
Documentation/kbuild/makefiles.txt | 10 ++++-
arch/Kconfig | 6 ---
scripts/Makefile.build | 32 +++++---------
scripts/link-vmlinux.sh | 91 ++++++++++++++------------------------
4 files changed, 51 insertions(+), 88 deletions(-)

diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index 71e9feefb63c..750aea9edd35 100644
--- a/Documentation/kbuild/makefiles.txt
+++ b/Documentation/kbuild/makefiles.txt
@@ -153,8 +153,14 @@ more details, with real examples.
configuration.

Kbuild compiles all the $(obj-y) files. It then calls
- "$(LD) -r" to merge these files into one built-in.o file.
- built-in.o is later linked into vmlinux by the parent Makefile.
+ "$(AR) rcSTP" to merge these files into one built-in.o file.
+ This is a thin archive without a symbol table, which makes it
+ unsuitable as a linker input.
+
+ The scripts/link-vmlinux.sh script later makes an aggregate
+ built-in.o with "${AR} rcsTP", which creates the thin archive
+ with a symbol table and an index, making it a valid input for
+ the final vmlinux link passes.

The order of files in $(obj-y) is significant. Duplicates in
the lists are allowed: the first instance will be linked into
diff --git a/arch/Kconfig b/arch/Kconfig
index 76c0b54443b1..8e0d665c8d53 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -596,12 +596,6 @@ config CC_STACKPROTECTOR_AUTO

endchoice

-config THIN_ARCHIVES
- def_bool y
- help
- Select this if the architecture wants to use thin archives
- instead of ld -r to create the built-in.o files.
-
config LD_DEAD_CODE_DATA_ELIMINATION
bool
help
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 47cddf32aeba..c43df53c7cce 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -450,15 +450,13 @@ $(sort $(subdir-obj-y)): $(subdir-ym) ;
#
ifdef builtin-target

-ifdef CONFIG_THIN_ARCHIVES
- cmd_make_builtin = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS)
- cmd_make_empty_builtin = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS)
- quiet_cmd_link_o_target = AR $@
-else
- cmd_make_builtin = $(LD) $(ld_flags) -r -o
- cmd_make_empty_builtin = rm -f $@; $(AR) rcs$(KBUILD_ARFLAGS)
- quiet_cmd_link_o_target = LD $@
-endif
+# built-in.o archives are made with no symbol table or index which
+# makes them small and fast, but unable to be used by the linker.
+# scripts/link-vmlinux.sh builds an aggregate built-in.o with a symbol
+# table and index.
+cmd_make_builtin = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS)
+cmd_make_empty_builtin = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS)
+quiet_cmd_link_o_target = AR $@

# If the list of objects to link is empty, just create an empty built-in.o
cmd_link_o_target = $(if $(strip $(obj-y)),\
@@ -491,11 +489,8 @@ $(modorder-target): $(subdir-ym) FORCE
ifdef lib-target
quiet_cmd_link_l_target = AR $@

-ifdef CONFIG_THIN_ARCHIVES
- cmd_link_l_target = rm -f $@; $(AR) rcsTP$(KBUILD_ARFLAGS) $@ $(lib-y)
-else
- cmd_link_l_target = rm -f $@; $(AR) rcs$(KBUILD_ARFLAGS) $@ $(lib-y)
-endif
+# lib target archives do get a symbol table and index
+cmd_link_l_target = rm -f $@; $(AR) rcsTP$(KBUILD_ARFLAGS) $@ $(lib-y)

$(lib-target): $(lib-y) FORCE
$(call if_changed,link_l_target)
@@ -543,13 +538,8 @@ $($(subst $(obj)/,,$(@:.o=-m)))), $^)

cmd_link_multi-link = $(LD) $(ld_flags) -r -o $@ $(link_multi_deps) $(cmd_secanalysis)

-ifdef CONFIG_THIN_ARCHIVES
- quiet_cmd_link_multi-y = AR $@
- cmd_link_multi-y = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS) $@ $(link_multi_deps)
-else
- quiet_cmd_link_multi-y = LD $@
- cmd_link_multi-y = $(cmd_link_multi-link)
-endif
+quiet_cmd_link_multi-y = AR $@
+cmd_link_multi-y = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS) $@ $(link_multi_deps)

quiet_cmd_link_multi-m = LD [M] $@
cmd_link_multi-m = $(cmd_link_multi-link)
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index c0d129d7f430..a55c24a86133 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -55,13 +55,11 @@ info()
#
archive_builtin()
{
- if [ -n "${CONFIG_THIN_ARCHIVES}" ]; then
- info AR built-in.o
- rm -f built-in.o;
- ${AR} rcsTP${KBUILD_ARFLAGS} built-in.o \
- ${KBUILD_VMLINUX_INIT} \
- ${KBUILD_VMLINUX_MAIN}
- fi
+ info AR built-in.o
+ rm -f built-in.o;
+ ${AR} rcsTP${KBUILD_ARFLAGS} built-in.o \
+ ${KBUILD_VMLINUX_INIT} \
+ ${KBUILD_VMLINUX_MAIN}
}

# Link of vmlinux.o used for section mismatch analysis
@@ -70,20 +68,13 @@ modpost_link()
{
local objects

- if [ -n "${CONFIG_THIN_ARCHIVES}" ]; then
- objects="--whole-archive \
- built-in.o \
- --no-whole-archive \
- --start-group \
- ${KBUILD_VMLINUX_LIBS} \
- --end-group"
- else
- objects="${KBUILD_VMLINUX_INIT} \
- --start-group \
- ${KBUILD_VMLINUX_MAIN} \
- ${KBUILD_VMLINUX_LIBS} \
- --end-group"
- fi
+ objects="--whole-archive \
+ built-in.o \
+ --no-whole-archive \
+ --start-group \
+ ${KBUILD_VMLINUX_LIBS} \
+ --end-group"
+
${LD} ${LDFLAGS} -r -o ${1} ${objects}
}

@@ -96,46 +87,28 @@ vmlinux_link()
local objects

if [ "${SRCARCH}" != "um" ]; then
- if [ -n "${CONFIG_THIN_ARCHIVES}" ]; then
- objects="--whole-archive \
- built-in.o \
- --no-whole-archive \
- --start-group \
- ${KBUILD_VMLINUX_LIBS} \
- --end-group \
- ${1}"
- else
- objects="${KBUILD_VMLINUX_INIT} \
- --start-group \
- ${KBUILD_VMLINUX_MAIN} \
- ${KBUILD_VMLINUX_LIBS} \
- --end-group \
- ${1}"
- fi
-
- ${LD} ${LDFLAGS} ${LDFLAGS_vmlinux} -o ${2} \
+ objects="--whole-archive \
+ built-in.o \
+ --no-whole-archive \
+ --start-group \
+ ${KBUILD_VMLINUX_LIBS} \
+ --end-group \
+ ${1}"
+
+ ${LD} ${LDFLAGS} ${LDFLAGS_vmlinux} -o ${2} \
-T ${lds} ${objects}
else
- if [ -n "${CONFIG_THIN_ARCHIVES}" ]; then
- objects="-Wl,--whole-archive \
- built-in.o \
- -Wl,--no-whole-archive \
- -Wl,--start-group \
- ${KBUILD_VMLINUX_LIBS} \
- -Wl,--end-group \
- ${1}"
- else
- objects="${KBUILD_VMLINUX_INIT} \
- -Wl,--start-group \
- ${KBUILD_VMLINUX_MAIN} \
- ${KBUILD_VMLINUX_LIBS} \
- -Wl,--end-group \
- ${1}"
- fi
-
- ${CC} ${CFLAGS_vmlinux} -o ${2} \
- -Wl,-T,${lds} \
- ${objects} \
+ objects="-Wl,--whole-archive \
+ built-in.o \
+ -Wl,--no-whole-archive \
+ -Wl,--start-group \
+ ${KBUILD_VMLINUX_LIBS} \
+ -Wl,--end-group \
+ ${1}"
+
+ ${CC} ${CFLAGS_vmlinux} -o ${2} \
+ -Wl,-T,${lds} \
+ ${objects} \
-lutil -lrt -lpthread
rm -f linux
fi
--
2.15.1