[*] XUANTIE ISA in AFLAGS with -march=_xtheadc 打开这个选项编译最后链接会找不到一些东西，why ?

[280185386]

ubuntu 18.04
Xuantie-900-gcc-linux-6.6.0-glibc-x86_64-V2.10.0
linux-xuantie-kernel 6.36 11eb4c8178644b373fe50a7b583942a036a3429

AR built-in.a
AR vmlinux.a
LD vmlinux.o
OBJCOPY modules.builtin.modinfo
GEN modules.builtin
MODPOST Module.symvers
CC .vmlinux.export.o
UPD include/generated/utsversion.h
CC init/version-timestamp.o
LD .tmp_vmlinux.kallsyms1
riscv64-unknown-linux-gnu-ld: ./drivers/firmware/efi/libstub/fdt.stub.o: in function fdt32_ld': /home/eda/linux/linux-xuantie-kernel/./include/linux/../../scripts/dtc/libfdt/libfdt.h:145: undefined reference to __efistub___thead_uread4'
riscv64-unknown-linux-gnu-ld: ./drivers/firmware/efi/libstub/gop.stub.o: in function setup_gop': /home/eda/linux/linux-xuantie-kernel/drivers/firmware/efi/libstub/gop.c:542: undefined reference to __efistub___thead_uread4'
riscv64-unknown-linux-gnu-ld: /home/eda/linux/linux-xuantie-kernel/drivers/firmware/efi/libstub/gop.c:542: undefined reference to __efistub___thead_uwrite4' riscv64-unknown-linux-gnu-ld: /home/eda/linux/linux-xuantie-kernel/drivers/firmware/efi/libstub/gop.c:549: undefined reference to __efistub___thead_uwrite4'
riscv64-unknown-linux-gnu-ld: /home/eda/linux/linux-xuantie-kernel/drivers/firmware/efi/libstub/gop.c:551: undefined reference to __efistub___thead_uread4' riscv64-unknown-linux-gnu-ld: /home/eda/linux/linux-xuantie-kernel/drivers/firmware/efi/libstub/gop.c:551: undefined reference to __efistub___thead_uwrite4'
riscv64-unknown-linux-gnu-ld: ./drivers/firmware/efi/libstub/lib-fdt.stub.o: in function fdt32_ld': /home/eda/linux/linux-xuantie-kernel/./scripts/dtc/libfdt/libfdt.h:145: undefined reference to __efistub___thead_uread4'
riscv64-unknown-linux-gnu-ld: ./drivers/firmware/efi/libstub/lib-fdt_ro.stub.o: in function fdt32_ld': /home/eda/linux/linux-xuantie-kernel/./scripts/dtc/libfdt/libfdt.h:145: undefined reference to __efistub___thead_uread4'
riscv64-unknown-linux-gnu-ld: ./drivers/firmware/efi/libstub/lib-fdt_rw.stub.o: in function fdt32_ld': /home/eda/linux/linux-xuantie-kernel/./scripts/dtc/libfdt/libfdt.h:145: undefined reference to __efistub___thead_uread4'
riscv64-unknown-linux-gnu-ld: ./drivers/firmware/efi/libstub/lib-fdt_sw.stub.o: in function fdt32_ld': /home/eda/linux/linux-xuantie-kernel/./scripts/dtc/libfdt/libfdt.h:145: undefined reference to __efistub___thead_uread4'
riscv64-unknown-linux-gnu-ld: ./drivers/firmware/efi/libstub/riscv.stub.o: in function get_boot_hartid_from_fdt': /home/eda/linux/linux-xuantie-kernel/drivers/firmware/efi/libstub/riscv.c:39: undefined reference to __efistub___thead_uread8'
riscv64-unknown-linux-gnu-ld: ./drivers/firmware/efi/libstub/tpm.stub.o: in function __calc_tpm2_event_size': /home/eda/linux/linux-xuantie-kernel/./include/linux/tpm_eventlog.h:205: undefined reference to __efistub___thead_uread4'
riscv64-unknown-linux-gnu-ld: /home/eda/linux/linux-xuantie-kernel/./include/linux/tpm_eventlog.h:206: undefined reference to __efistub___thead_uread4' riscv64-unknown-linux-gnu-ld: /home/eda/linux/linux-xuantie-kernel/./include/linux/tpm_eventlog.h:201: undefined reference to __efistub___thead_uread4'
riscv64-unknown-linux-gnu-ld: /home/eda/linux/linux-xuantie-kernel/./include/linux/tpm_eventlog.h:202: undefined reference to __efistub___thead_uread4' riscv64-unknown-linux-gnu-ld: /home/eda/linux/linux-xuantie-kernel/./include/linux/tpm_eventlog.h:223: undefined reference to __efistub___thead_uread4'
riscv64-unknown-linux-gnu-ld: ./drivers/firmware/efi/libstub/tpm.stub.o:/home/eda/linux/linux-xuantie-kernel/./include/linux/tpm_eventlog.h:248: more undefined references to __efistub___thead_uread4' follow riscv64-unknown-linux-gnu-ld: ./drivers/firmware/efi/libstub/efi-stub-helper.stub.o: in function efi_measure_tagged_event':
/home/eda/linux/linux-xuantie-kernel/drivers/firmware/efi/libstub/efi-stub-helper.c:252: undefined reference to __efistub___thead_uwrite4' riscv64-unknown-linux-gnu-ld: /home/eda/linux/linux-xuantie-kernel/drivers/firmware/efi/libstub/efi-stub-helper.c:252: undefined reference to __efistub___thead_uwrite4'
riscv64-unknown-linux-gnu-ld: /home/eda/linux/linux-xuantie-kernel/drivers/firmware/efi/libstub/efi-stub-helper.c:252: undefined reference to __efistub___thead_uwrite4' riscv64-unknown-linux-gnu-ld: /home/eda/linux/linux-xuantie-kernel/drivers/firmware/efi/libstub/efi-stub-helper.c:252: undefined reference to __efistub___thead_uwrite4'
riscv64-unknown-linux-gnu-ld: /home/eda/linux/linux-xuantie-kernel/drivers/firmware/efi/libstub/efi-stub-helper.c:260: undefined reference to __efistub___thead_uwrite4' riscv64-unknown-linux-gnu-ld: ./drivers/firmware/efi/libstub/efi-stub-helper.stub.o:/home/eda/linux/linux-xuantie-kernel/drivers/firmware/efi/libstub/efi-stub-helper.c:260: more undefined references to __efistub___thead_uwrite4' follow
riscv64-unknown-linux-gnu-ld: arch/riscv/kernel/pi/lib-fdt.pi.o: in function fdt32_ld': /home/eda/linux/linux-xuantie-kernel/./scripts/dtc/libfdt/libfdt.h:145: undefined reference to __pi___thead_uread4'
riscv64-unknown-linux-gnu-ld: arch/riscv/kernel/pi/lib-fdt_ro.pi.o: in function fdt32_ld': /home/eda/linux/linux-xuantie-kernel/./scripts/dtc/libfdt/libfdt.h:145: undefined reference to __pi___thead_uread4'
scripts/Makefile.vmlinux:37: recipe for target 'vmlinux' failed
make[2]: *** [vmlinux] Error 1
/home/eda/linux/linux-xuantie-kernel/Makefile:1164: recipe for target 'vmlinux' failed
make[1]: *** [vmlinux] Error 2
Makefile:234: recipe for target '__sub-make' failed