[M68k] error: unknown register name 'sp' in asm when trying to build Linux kernel

[glaubitz]

Trying to build the Linux/m68k kernel with clang has improved quite a bit, but unfortunately still fails early:

glaubitz@node54:/data/home/glaubitz/linux> make CC=clang -j32
  SYNC    include/config/auto.conf.cmd
*
* Restart config...
*
*
* Memory initialization
*
Initialize kernel stack variables at function entry
> 1. no automatic stack variable initialization (weakest) (INIT_STACK_NONE)
  2. pattern-init everything (strongest) (INIT_STACK_ALL_PATTERN) (NEW)
  3. zero-init everything (strongest and safest) (INIT_STACK_ALL_ZERO) (NEW)
choice[1-3?]: 
Enable heap memory zeroing on allocation by default (INIT_ON_ALLOC_DEFAULT_ON) [N/y/?] n
Enable heap memory zeroing on free by default (INIT_ON_FREE_DEFAULT_ON) [N/y/?] n
*
* Kernel hardening options
*
Randomize layout of sensitive kernel structures
> 1. Disable structure layout randomization (RANDSTRUCT_NONE)
  2. Fully randomize structure layout (RANDSTRUCT_FULL) (NEW)
choice[1-2?]: 
  SYSHDR  arch/m68k/include/generated/uapi/asm/unistd_32.h
  SYSTBL  arch/m68k/include/generated/asm/syscall_table.h
  UPD     include/generated/compile.h
  HOSTCC  scripts/asn1_compiler
  HOSTCC  scripts/kallsyms
  UPD     include/config/kernel.release
  UPD     include/generated/utsrelease.h
  HOSTCC  scripts/mod/mk_elfconfig
  CC      scripts/mod/empty.o
  CC      scripts/mod/devicetable-offsets.s
  MKELF   scripts/mod/elfconfig.h
  HOSTCC  scripts/mod/modpost.o
  HOSTCC  scripts/mod/file2alias.o
  HOSTCC  scripts/mod/sumversion.o
  HOSTLD  scripts/mod/modpost
  CC      kernel/bounds.s
  CHKSHA1 include/linux/atomic/atomic-arch-fallback.h
  CHKSHA1 include/linux/atomic/atomic-long.h
  CHKSHA1 include/linux/atomic/atomic-instrumented.h
  CC      arch/m68k/kernel/asm-offsets.s
In file included from arch/m68k/kernel/asm-offsets.c:15:
In file included from ./include/linux/sched.h:12:
./arch/m68k/include/asm/current.h:29:54: error: unknown register name 'sp' in asm
   29 | register unsigned long current_stack_pointer __asm__("sp");
      |                                                      ^
1 error generated.
make[2]: *** [scripts/Makefile.build:116: arch/m68k/kernel/asm-offsets.s] Error 1
make[1]: *** [/data/home/glaubitz/linux/Makefile:1287: prepare0] Error 2
make: *** [Makefile:234: __sub-make] Error 2
glaubitz@node54:/data/home/glaubitz/linux>

It seems that that the m68k backend needs to learn about register names or at least the SP register.

CC @mshockwave @0x59616e

[llvmbot]

@llvm/issue-subscribers-backend-m68k

Author: John Paul Adrian Glaubitz (glaubitz)

Trying to build the Linux/m68k kernel with clang has improved quite a bit, but unfortunately still fails early:

glaubitz@<!-- -->node54:/data/home/glaubitz/linux&gt; make CC=clang -j32
  SYNC    include/config/auto.conf.cmd
*
* Restart config...
*
*
* Memory initialization
*
Initialize kernel stack variables at function entry
&gt; 1. no automatic stack variable initialization (weakest) (INIT_STACK_NONE)
  2. pattern-init everything (strongest) (INIT_STACK_ALL_PATTERN) (NEW)
  3. zero-init everything (strongest and safest) (INIT_STACK_ALL_ZERO) (NEW)
choice[1-3?]: 
Enable heap memory zeroing on allocation by default (INIT_ON_ALLOC_DEFAULT_ON) [N/y/?] n
Enable heap memory zeroing on free by default (INIT_ON_FREE_DEFAULT_ON) [N/y/?] n
*
* Kernel hardening options
*
Randomize layout of sensitive kernel structures
&gt; 1. Disable structure layout randomization (RANDSTRUCT_NONE)
  2. Fully randomize structure layout (RANDSTRUCT_FULL) (NEW)
choice[1-2?]: 
  SYSHDR  arch/m68k/include/generated/uapi/asm/unistd_32.h
  SYSTBL  arch/m68k/include/generated/asm/syscall_table.h
  UPD     include/generated/compile.h
  HOSTCC  scripts/asn1_compiler
  HOSTCC  scripts/kallsyms
  UPD     include/config/kernel.release
  UPD     include/generated/utsrelease.h
  HOSTCC  scripts/mod/mk_elfconfig
  CC      scripts/mod/empty.o
  CC      scripts/mod/devicetable-offsets.s
  MKELF   scripts/mod/elfconfig.h
  HOSTCC  scripts/mod/modpost.o
  HOSTCC  scripts/mod/file2alias.o
  HOSTCC  scripts/mod/sumversion.o
  HOSTLD  scripts/mod/modpost
  CC      kernel/bounds.s
  CHKSHA1 include/linux/atomic/atomic-arch-fallback.h
  CHKSHA1 include/linux/atomic/atomic-long.h
  CHKSHA1 include/linux/atomic/atomic-instrumented.h
  CC      arch/m68k/kernel/asm-offsets.s
In file included from arch/m68k/kernel/asm-offsets.c:15:
In file included from ./include/linux/sched.h:12:
./arch/m68k/include/asm/current.h:29:54: error: unknown register name 'sp' in asm
   29 | register unsigned long current_stack_pointer __asm__("sp");
      |                                                      ^
1 error generated.
make[2]: *** [scripts/Makefile.build:116: arch/m68k/kernel/asm-offsets.s] Error 1
make[1]: *** [/data/home/glaubitz/linux/Makefile:1287: prepare0] Error 2
make: *** [Makefile:234: __sub-make] Error 2
glaubitz@<!-- -->node54:/data/home/glaubitz/linux&gt;

It seems that that the m68k backend needs to learn about register names or at least the SP register.

CC @mshockwave @0x59616e