Tag Archive for 'powerpc'

Cross-compiling a PowerPC64 LE kernel and hitting a GCC bug

Being new at OzLabs I’m dipping my toes into various projects and having a play with PowerPC and so I thought I’d cross-compile the Linux kernel on Fedora. Traditionally PowerPC has been big endian, however it also supports little endian so I wanted to build all the things.

Fedora uses a single cross toolchain that can build all four variants, whereas Debian/Ubuntu splits this out into two different toolchains (a BE and an LE one).

Install dependencies in Fedora:
$ sudo dnf install gcc make binutils-powerpc64-linux-gnu gcc-powerpc64-linux-gnu gcc-c++-powerpc64-linux-gnu bc ncurses-devel

Get the v4.2 kernel:
$ git clone https://github.com/torvalds/linux.git --branch v4.2 --depth 1 && cd linux

Successful big endian build of the kernel, using the default config for pseries:
$ ARCH=powerpc CROSS_COMPILE=powerpc64-linux-gnu- make pseries_defconfig
$ ARCH=powerpc CROSS_COMPILE=powerpc64-linux-gnu- make -j$(nproc)
# clean after success
$ ARCH=powerpc CROSS_COMPILE=powerpc64-linux-gnu- make clean
$ ARCH=powerpc CROSS_COMPILE=powerpc64-linux-gnu- make mrproper

Building a little endian kernel however, resulted in a linker problem:
$ ARCH=powerpc CROSS_COMPILE=powerpc64-linux-gnu- make pseries_defconfig
$ ARCH=powerpc CROSS_COMPILE=powerpc64-linux-gnu- make menuconfig
# change architecture to little endian:
# Endianness selection (Build big endian kernel) --->
# (X) Build little endian kernel
$ ARCH=powerpc CROSS_COMPILE=powerpc64-linux-gnu- make V=1

Here was the result:
powerpc64-linux-gnu-gcc -mlittle-endian -mno-strict-align -m64 -Wp,-MD,arch/powerpc/kernel/vdso64/.vdso64.so.dbg.d -nostdinc -isystem /usr/lib/gcc/powerpc64-linux-gnu/5.2.1/include -I./arch/powerpc/include -Iarch/powerpc/include/generated/uapi -Iarch/powerpc/include/generated -Iinclude -I./arch/powerpc/include/uapi -Iarch/powerpc/include/generated/uapi -I./include/uapi -Iinclude/generated/uapi -include ./include/linux/kconfig.h -D__KERNEL__ -Iarch/powerpc -DHAVE_AS_ATHIGH=1 -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -Werror-implicit-function-declaration -Wno-format-security -std=gnu89 -msoft-float -pipe -Iarch/powerpc -mtraceback=no -mabi=elfv2 -mcmodel=medium -mno-pointers-to-nested-functions -mcpu=power7 -mno-altivec -mno-vsx -mno-spe -mspe=no -funit-at-a-time -fno-dwarf2-cfi-asm -mno-string -Wa,-maltivec -fno-delete-null-pointer-checks -O2 --param=allow-store-data-races=0 -Wframe-larger-than=2048 -fno-stack-protector -Wno-unused-but-set-variable -fomit-frame-pointer -fno-var-tracking-assignments -Wdeclaration-after-statement -Wno-pointer-sign -fno-strict-overflow -fconserve-stack -Werror=implicit-int -Werror=strict-prototypes -Werror=date-time -DCC_HAVE_ASM_GOTO -Werror -shared -fno-common -fno-builtin -nostdlib -Wl,-soname=linux-vdso64.so.1 -Wl,--hash-style=sysv -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(vdso64.so)" -D"KBUILD_MODNAME=KBUILD_STR(vdso64.so)" -Wl,-T arch/powerpc/kernel/vdso64/vdso64.lds arch/powerpc/kernel/vdso64/sigtramp.o arch/powerpc/kernel/vdso64/gettimeofday.o arch/powerpc/kernel/vdso64/datapage.o arch/powerpc/kernel/vdso64/cacheflush.o arch/powerpc/kernel/vdso64/note.o arch/powerpc/kernel/vdso64/getcpu.o -o arch/powerpc/kernel/vdso64/vdso64.so.dbg
/usr/bin/powerpc64-linux-gnu-ld: arch/powerpc/kernel/vdso64/sigtramp.o: file class ELFCLASS64 incompatible with ELFCLASS32
/usr/bin/powerpc64-linux-gnu-ld: final link failed: File in wrong format
collect2: error: ld returned 1 exit status
arch/powerpc/kernel/vdso64/Makefile:26: recipe for target 'arch/powerpc/kernel/vdso64/vdso64.so.dbg' failed
make[2]: *** [arch/powerpc/kernel/vdso64/vdso64.so.dbg] Error 1
scripts/Makefile.build:403: recipe for target 'arch/powerpc/kernel/vdso64' failed
make[1]: *** [arch/powerpc/kernel/vdso64] Error 2
Makefile:949: recipe for target 'arch/powerpc/kernel' failed
make: *** [arch/powerpc/kernel] Error 2

All those files were 64bit, however:
arch/powerpc/kernel/vdso64/cacheflush.o: ELF 64-bit LSB relocatable, 64-bit PowerPC or cisco 7500, version 1 (SYSV), not stripped
arch/powerpc/kernel/vdso64/datapage.o: ELF 64-bit LSB relocatable, 64-bit PowerPC or cisco 7500, version 1 (SYSV), not stripped
arch/powerpc/kernel/vdso64/getcpu.o: ELF 64-bit LSB relocatable, 64-bit PowerPC or cisco 7500, version 1 (SYSV), not stripped
arch/powerpc/kernel/vdso64/gettimeofday.o: ELF 64-bit LSB relocatable, 64-bit PowerPC or cisco 7500, version 1 (SYSV), not stripped
arch/powerpc/kernel/vdso64/note.o: ELF 64-bit LSB relocatable, 64-bit PowerPC or cisco 7500, version 1 (SYSV), not stripped
arch/powerpc/kernel/vdso64/sigtramp.o: ELF 64-bit LSB relocatable, 64-bit PowerPC or cisco 7500, version 1 (SYSV), not stripped

An strace of the failing powerpc64-linux-gnu-gcc command above showed that collect2 (and ld) were being called with an option setting the format to 32bit:
24904 execve("/usr/libexec/gcc/powerpc64-linux-gnu/5.2.1/collect2", ["/usr/libexec/gcc/powerpc64-linux"..., "-plugin", "/usr/libexec/gcc/powerpc64-linux"..., "-plugin-opt=/usr/libexec/gcc/pow"..., "-plugin-opt=-fresolution=/tmp/cc"..., "--sysroot=/usr/powerpc64-linux-g"..., "--build-id", "--no-add-needed", "--eh-frame-hdr", "--hash-style=gnu", "-shared", "--oformat", "elf32-powerpcle", "-m", "elf64lppc", "-o", ...], [/* 66 vars */]

Alan Modra tracked it down to some 32bit hard-coded entries in GCC sysv4.h and sysv4le.h and submitted a patch to the GCC mailing list (Red Hat bug).

I re-built the Fedora cross-gcc package with his patch and it solved the linker problem for me. Hurrah!