Makefile没有针对目标的规则

Question

Make complains that there is no rule for target 'build/libc/string/strlen.c' when it's clearly defined. Weirdly, it successfully compiled all but one dependency for 'build/libc/libc.a'. I had, or at least attempted to, disabled the builtin implicit rules and variables to avoid spending hours debugging while pulling my hair out but it doesn't seem to help because I'm completely lost.

Makefile:

.SUFFIXES:

MAKEFLAGS += -rR

STD = gnu11
CFLAGS = -O2 -g -ffreestanding -fbuiltin -Wall -Wno-div-by-zero -D__is_vos_kernel__ -Iinclude
LFLAGS = -O2 -g -ffreestanding -fbuiltin -Wall -Wextra
LIBC_FLAGS = -O2 -g -D__is_vos_libc__ -Iinclude
LIBK_FLAGS = -O2 -g -ffreestanding -fbuiltin -D__is_vos_libc__ -Iinclude -D__is_vos_kernel__

CC = i386-elf-gcc
LD = i386-elf-ld
AR = i386-elf-ar
AS = /usr/local/bin/nasm

SYSROOT = sysroot
BUILDDIR = builddir

SYSARG = --sysroot=sysroot -isystem=/usr/include

LIBC_OBJECTS = $(wildcard libc/*.c)
LIBC_HEADERS = $(wildcard libc/*.h)
LLIBC_HEADERS = $(wildcard sysroot/usr/include/*.h)

header:=$(shell find libc -type f -name "*.h")

prepare-dir:
    mkdir -p sysroot/usr/include sysroot/usr/lib build

sysroot/usr/include/%.h: libc/%.h prepare-dir
    cd libc; rsync -R $(<:libc/%=%) ../sysroot/usr/include

prepare-headers: $(addprefix sysroot/usr/include/, $(header:libc/%=%))
    @echo $^

prepare: prepare-dir prepare-headers

build/libc/%.o: libc/%.c prepare
    $(CC) $(SYSARG) -c $< -o $@ -std=$(STD) $(LIBC_FLAGS)

libc_objects = $(shell find libc -type f -name "*.c")
libco_pre = $(addprefix build/, $(libc_objects)))

build/libc/libc.a: $(libco_pre:.c=.o)
    $(AR) rcs $@ $^

clean:
    find . -type f -name "*.o" -delete
    find sysroot -type f -name "*" -delete
    # find sysroot -type d -name "*" -delete
    find build -type f -name "*" -delete
    # find build -type d -name "*" -delete

Command log:

G16-MACBOOKPRO:VioletOS ghifari160$ make -rR build/libc/libc.a
mkdir -p sysroot/usr/include sysroot/usr/lib build
cd libc; rsync -R stdbool.h ../sysroot/usr/include
cd libc; rsync -R stdint.h ../sysroot/usr/include
cd libc; rsync -R stdlib.h ../sysroot/usr/include
cd libc; rsync -R string.h ../sysroot/usr/include
cd libc; rsync -R sys/cdefs.h ../sysroot/usr/include
sysroot/usr/include/stdbool.h sysroot/usr/include/stdint.h sysroot/usr/include/stdlib.h sysroot/usr/include/string.h sysroot/usr/include/sys/cdefs.h
i386-elf-gcc --sysroot=sysroot -isystem=/usr/include -c libc/stdlib/abort.c -o build/libc/stdlib/abort.o -std=gnu11 -O2 -g -D__is_vos_libc__ -Iinclude
i386-elf-gcc --sysroot=sysroot -isystem=/usr/include -c libc/string/malloc.c -o build/libc/string/malloc.o -std=gnu11 -O2 -g -D__is_vos_libc__ -Iinclude
i386-elf-gcc --sysroot=sysroot -isystem=/usr/include -c libc/string/memcmp.c -o build/libc/string/memcmp.o -std=gnu11 -O2 -g -D__is_vos_libc__ -Iinclude
i386-elf-gcc --sysroot=sysroot -isystem=/usr/include -c libc/string/memcpy.c -o build/libc/string/memcpy.o -std=gnu11 -O2 -g -D__is_vos_libc__ -Iinclude
i386-elf-gcc --sysroot=sysroot -isystem=/usr/include -c libc/string/memmove.c -o build/libc/string/memmove.o -std=gnu11 -O2 -g -D__is_vos_libc__ -Iinclude
i386-elf-gcc --sysroot=sysroot -isystem=/usr/include -c libc/string/memset.c -o build/libc/string/memset.o -std=gnu11 -O2 -g -D__is_vos_libc__ -Iinclude
i386-elf-gcc --sysroot=sysroot -isystem=/usr/include -c libc/string/strcat.c -o build/libc/string/strcat.o -std=gnu11 -O2 -g -D__is_vos_libc__ -Iinclude
make: *** No rule to make target `build/libc/string/strlen.c)', needed by `build/libc/libc.a'.  Stop.

Answer 1

notice the closing parenthesis at the end of build/libc/string/strlen.c) - it prevents your :.c=.o substitution from functioning properly, so make tries to look for a source file in the build directory, which does of course not exist.

the root cause is likely that this line has one closing parenthesis too many:

libco_pre = $(addprefix build/, $(libc_objects)))
                                      here -----^

which adds a closing parenthesis to the last target in the list. This is why all of the previous targets had been built correctly.