bootstrapping arm64

I'm still working on perl-cross-debian (just uploaded 0.0.2) and there's more to do on that with upstream but part of the reason to work on perl cross-building is to do what I can to help with the ARM64 port.

So, I went back to Wookey's talk at DebConf12 which leads to the current list of cross-build results for arm64 and started through the list.

coreutils is listed as failing but that was an archive error (MD5sum hash mismatch), so that just needs a retry. I don't have access to that buildd, yet, so nothing I can do there.

Next on the list (excluding those just waiting for build-deps) was klibc.

  aarch64-linux-gnu-gcc -Wp,-MD,usr/klibc/.__static_init.o.d  -nostdinc -iwithprefix 

include -I/«PKGBUILDDIR»/usr/include/arch/x86_64 -Iusr/include/arch/x86_64 

-I/«PKGBUILDDIR»/usr/include/bits64 

-Iusr/include/bits64 -I/«PKGBUILDDIR»/usr/klibc/../include 

-Iusr/klibc/../include -I/«PKGBUILDDIR»/usr/include -Iusr/include 

-I/«PKGBUILDDIR»/linux/include -Ilinux/include 

-I/«PKGBUILDDIR»/linux/arch/x86/include -Ilinux/arch/x86/include 

-D__KLIBC__=2 -D__KLIBC_MINOR__=0 -D_BITSIZE=64 -fno-stack-protector -fwrapv -m64 -Os 

-fno-asynchronous-unwind-tables -fomit-frame-pointer -falign-functions=1 -falign-jumps=1 -falign-loops=1 

-W -Wall -Wno-sign-compare -Wno-unused-parameter -c -o usr/klibc/__static_init.o usr/klibc/__static_init.c

aarch64-linux-gnu-gcc: error: unrecognized command line option '-m64'

make[4]: *** [usr/klibc/__static_init.o] Error 1

Turns out that this is a build failure I understood, at least initially. A little digging and a trivial patch was begun:

--- a/usr/klibc/arch/arm/MCONFIG

+++ b/usr/klibc/arch/arm/MCONFIG

@@ -30,6 +30,13 @@

 ifeq ($(CONFIG_AEABI),y)

 KLIBCREQFLAGS += -mabi=aapcs-linux -mno-thumb-interwork

 else

+# aarch64

+ifeq ($(CONFIG_AARCH64),y)

+KLIBCREQFLAGS +=

+KLIBCOPTFLAGS += -mgeneral-regs-only

+else

 KLIBCREQFLAGS += -mabi=apcs-gnu -mno-thumb-interwork

 endif

 endif

+endif

+

Alongside a trivial change to debian/rules

ifeq ($(DEB_HOST_ARCH),arm64)

DEB_MAKE_ENVVARS := ARCH=arm CONFIG_AARCH64=y CPU_ARCH=armv8-a CPU_TUNE=generic

endif

OK, then things get a bit more awkward,

....

code/debian/cross/klibc/klibc-2.0.1/linux/arch/arm/include -Ilinux/arch/arm/include -D__KLIBC__=2 

-D__KLIBC_MINOR__=0 -D_BITSIZE=32 -fno-stack-protector -fwrapv -fno-exceptions -Os 

-march=armv8-a -mtune=generic -mgeneral-regs-only -W -Wall -Wno-sign-compare -Wno-unused-parameter 

-c -o ../foo.o usr/klibc/arch/arm/crt0.S

usr/klibc/arch/arm/crt0.S: Assembler messages:

usr/klibc/arch/arm/crt0.S:19: Error: operand 1 should be an integer register -- `mov r0,sp'

usr/klibc/arch/arm/crt0.S:20: Error: operand 1 should be an integer register -- `mov r1,#0'

Hmm. Assembly, well, yes, I've done assembly before, I know what mov should normally do, sp is likely to be the stack pointer .... where's my AARCH64 assembly PDF again... PRD03-GENC-010197 ...

OK, so maybe the r0 and r1 should be x0 and x1, hmm, that at least doesn't raise assembly errors. So a tentative change:

--- a/usr/klibc/arch/arm/crt0.S

+++ b/usr/klibc/arch/arm/crt0.S

@@ -15,9 +15,13 @@

 #ifdef __thumb__

 	.thumb_func

 #endif

-

+#ifdef __aarch64__

+_start: mov x0, sp

+	mov x1, #0

+	bl __libc_init

+#else

 _start:	mov	r0, sp

 	mov	r1, #0

 	bl	__libc_init

-

+#endif

 	.size _start,.-_start

Next stage, however, leaves me quite a bit more lost:

....

klibc-2.0.1/linux/arch/arm/include -Ilinux/arch/arm/include 

-D__KLIBC__=2 -D__KLIBC_MINOR__=0 -D_BITSIZE=32 -fno-stack-protector -fwrapv -fno-exceptions -Os 

-march=armv8-a -mtune=generic -mgeneral-regs-only -W -Wall -Wno-sign-compare -Wno-unused-parameter 

-c -o usr/klibc/arch/arm/setjmp.o usr/klibc/arch/arm/setjmp.S

usr/klibc/arch/arm/setjmp.S: Assembler messages:

usr/klibc/arch/arm/setjmp.S:32: Error: unknown mnemonic `stmia' -- `stmia r0,{r4,r5,r6,r7,r8,r9,r10,fp,sp,lr}'

usr/klibc/arch/arm/setjmp.S:33: Error: operand 1 should be an integer register -- `mov r0,#0'

usr/klibc/arch/arm/setjmp.S:34: Error: operand 1 should be an integer register -- `mov pc,lr'

usr/klibc/arch/arm/setjmp.S:42: Error: unknown mnemonic `ldmia' -- `ldmia r0,{r4,r5,r6,r7,r8,r9,r10,fp,sp,lr}'

usr/klibc/arch/arm/setjmp.S:43: Error: unknown mnemonic `movs' -- `movs r0,r1'

usr/klibc/arch/arm/setjmp.S:44: Error: unknown mnemonic `moveq' -- `moveq r0,#1'

usr/klibc/arch/arm/setjmp.S:45: Error: operand 1 should be an integer register -- `mov pc,lr'

make[5]: *** [usr/klibc/arch/arm/setjmp.o] Error 1

So now I'm out of my depth of AARCH64 assembly (apart from the recurrence of mov r0 vs mov x0 etc.). If the above is useful then maybe someone can work out what is wrong with setjmp.S or whether AARCH64 just means that klibc needs to gain a arch/arm64/ directory and not try to duplicate each entire assembly block within #ifdef clauses.

I don't really know where else to put an incomplete investigation like this, so it's here for anyone to find.

(Oh, and if you're reading those arm64 cross-build logs, then a few hundred occurrences of ldconfig: /usr/lib/aarch64-linux-gnu/*.so is for unknown machine 183. in every build log (success or fail) is apparently entirely normal until more packages get fixed. Really slows down scanning the build log.

I may try busybox or libusb next. libusb looks like a classic "you might have told me to cross-compile but I'm going to use g++ anyway because I know best" cross-building problem, indicative of yet another BDBS. sigh.

Resources:
Getting started with 64-bit ARM development
ARMv8 images for developers
AArch64 for everyone, Marcin Juszkiewicz
Howto/HelloAarch64 - Linaro wiki
AArch64 gcc options