clang ias: fatal error: error in backend: Unknown Arch: xscale

[arndb]

I hit this bug when building arch/arm/mm/copypage-xscale.c with the integrated assembler:

fatal error: error in backend: Unknown Arch: xscale
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0. Program arguments: /usr/bin/clang-12 -mlittle-endian -fmacro-prefix-map=/git/arm-soc/= -Wall -Wundef -Werror=strict-prototypes -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE -Werror=implicit-function-declaration -Werror=implicit-int -Werror=return-type -std=gnu89 --target=arm-linux-gnueabi --prefix=/home/arnd/cross/x86_64/gcc-10.1.0-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi- --gcc-toolchain=/home/arnd/cross/x86_64/gcc-10.1.0-nolibc/arm-linux-gnueabi -Werror=unknown-warning-option -msoft-float -fno-dwarf2-cfi-asm -fno-omit-frame-pointer -mabi=aapcs-linux -mfpu=vfp -meabi gnu -marm -march=armv5te -mtune=xscale -fno-delete-null-pointer-checks -O2 -Wframe-larger-than=1024 -fstack-protector -mno-global-merge -fno-omit-frame-pointer -fno-optimize-sibling-calls -mno-omit-leaf-frame-pointer -ftrivial-auto-var-init=pattern -pg -Wdeclaration-after-statement -Wvla -fno-strict-overflow -fno-stack-check -Werror=date-time -Werror=incompatible-pointer-types -Wa,-W -Wa,-mcpu=xscale -Werror -nostdinc -isystem /usr/lib/llvm-12/lib/clang/12.0.0/include -I/git/arm-soc/arch/arm/include -I./arch/arm/include/generated -I/git/arm-soc/include -I./include -I/git/arm-soc/arch/arm/include/uapi -I./arch/arm/include/generated/uapi -I/git/arm-soc/include/uapi -I./include/generated/uapi -include /git/arm-soc/include/linux/kconfig.h -include /git/arm-soc/include/linux/compiler_types.h -D__KERNEL__ -I/git/arm-soc/arch/arm/mach-ixp4xx/include -DKBUILD_ERR0 -D__LINUX_ARM_ARCH__=5 -Uarm -I /git/arm-soc/arch/arm/mm -I ./arch/arm/mm -DKBUILD_MODFILE="arch/arm/mm/copypage-xscale" -DKBUILD_BASENAME="copypage_xscale" -DKBUILD_MODNAME="copypage_xscale" -D__KBUILD_MODNAME=kmod_copypage_xscale -c -o arch/arm/mm/copypage-xscale.o /git/arm-soc/arch/arm/mm/copypage-xscale.c

[nickdesaulniers]

CONFIG_CPU_XSCALE?

[arndb]

This is the patch I have applied locally:

index 8fc8f3b91197..3cc74a4862c5 100644
--- a/arch/arm/mm/copypage-xsc3.c
+++ b/arch/arm/mm/copypage-xsc3.c
@@ -29,7 +29,7 @@ static void xsc3_mc_copy_user_page(void *kto, const void *kfrom)
        int tmp;
 
        asm volatile ("\
-.arch  xscale                                  \n\
+.arch  armv5te                                 \n\
        pld     [%1, #0]                        \n\
        pld     [%1, #32]                       \n\
 1:     pld     [%1, #64]                       \n\
@@ -81,7 +81,7 @@ void xsc3_mc_clear_user_highpage(struct page *page, unsigned long vaddr)
 {
        void *ptr, *kaddr = kmap_atomic(page);
        asm volatile ("\
-.arch  xscale                                  \n\
+.arch  armv5te                                 \n\
        mov     r1, %2                          \n\
        mov     r2, #0                          \n\
        mov     r3, #0                          \n\
diff --git a/arch/arm/mm/copypage-xscale.c b/arch/arm/mm/copypage-xscale.c
index eb5d338657d1..c7461755082b 100644
--- a/arch/arm/mm/copypage-xscale.c
+++ b/arch/arm/mm/copypage-xscale.c
@@ -41,7 +41,7 @@ static void mc_copy_user_page(void *from, void *to)
         * when prefetching destination as well.  (NP)
         */
        asm volatile ("\
-.arch xscale                                   \n\
+.arch armv5te                                  \n\
        pld     [%0, #0]                        \n\
        pld     [%0, #32]                       \n\
        pld     [%1, #0]                        \n\
@@ -107,7 +107,7 @@ xscale_mc_clear_user_highpage(struct page *page, unsigned long vaddr)
 {
        void *ptr, *kaddr = kmap_atomic(page);
        asm volatile("\
-.arch xscale                                   \n\
+.arch armv5te                                  \n\
        mov     r1, %2                          \n\
        mov     r2, #0                          \n\
        mov     r3, #0                          \n\

[jcai19]

Shall we remove the integrated-as label since IAS probably won't support XScale any time soon (#975)?

[arndb]

It should be a trivial fix to either change the kernel with the patch I suggested above, or to have IAS treat XScale as an alias for armv5te.

I don't think there is anything the kernel cares about in what gas considers xscale as opposed to standard armv5te. The iwmmxt support mentioned in #975 is an optional feature of both xscale and pj4, but most xscale processors don't actually support it if I remember correctly.

[jcai19]

Thanks for the clarification. I could help patch IAS if that's preferred, but it seems fixing them in kernel might be easier if what we see in #1276 (comment) are the only uses?

[DavidSpickett]

Fixing llvm would be quite easy, assuming you know what "xscale"'s features should be.

In llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp ARMTargetELFStreamer::emitArchDefaultAttributes there is a switch case and the xscale case is missing.

[DavidSpickett]

Posted for review: https://reviews.llvm.org/D104776

[nickdesaulniers]

$ ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make LLVM=1 LLVM_IAS=1 -j72 iop32x_defconfig arch/arm/mm/copypage-xscale.o

[DavidSpickett]

Landed https://reviews.llvm.org/rG558d9e82283e6b053b18091de6e56a5e208b7036