Re: error: gendwarfksyms: process_module: dwarf_get_units failed: no debugging information?

[Sami Tolvanen <samitolvanen@google.com>]

On Wed, Feb 12, 2025 at 07:55:45AM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   09fbf3d502050282bf47ab3babe1d4ed54dd1fd8
> commit: 9c3681f9b9fd12cdbc4a542df599f1837512f3d5 kbuild: Add gendwarfksyms as an alternative to genksyms
> date:   5 weeks ago
> config: s390-randconfig-002-20250212 (https://download.01.org/0day-ci/archive/20250212/202502120752.U3fOKScQ-lkp@intel.com/config)
> compiler: clang version 17.0.6 (https://github.com/llvm/llvm-project 6009708b4367171ccdbf4b5905cb6a803753fe18)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250212/202502120752.U3fOKScQ-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202502120752.U3fOKScQ-lkp@intel.com/
> 
> All error/warnings (new ones prefixed by >>):
> 
> >> error: gendwarfksyms: process_module: dwarf_get_units failed: no debugging information?
> --
>    In file included from <stdin>:3:
>    In file included from arch/s390/include/asm/asm-prototypes.h:4:
> >> include/linux/kvm_host.h:1908:24: warning: field 'desc' with variable sized type 'struct kvm_stats_desc' not at the end of a struct or class is a GNU extension [-Wgnu-variable-sized-type-not-at-end]
>     1908 |         struct kvm_stats_desc desc;
>          |                               ^
>    1 warning generated.
> >> error: gendwarfksyms: process_module: dwarf_get_units failed: no debugging information?

The issue appears to be that the files in arch/s390/purgatory are
always built without debugging information, even though they include
code that uses EXPORT_SYMBOL.

I suspect the correct solution here is to ignore the object files in
this directory when calculating modversions. The quick patch below
fixes the build issue for me. Masahiro, does this look reasonable to
you?

Sami


diff --git a/arch/s390/purgatory/Makefile b/arch/s390/purgatory/Makefile
index bdcf2a3b6c41..bdcecc19441d 100644
--- a/arch/s390/purgatory/Makefile
+++ b/arch/s390/purgatory/Makefile
@@ -28,6 +28,8 @@ KBUILD_AFLAGS := $(filter-out -DCC_USING_EXPOLINE,$(KBUILD_AFLAGS))
 PURGATORY_LDFLAGS := -nostdlib -z nodefaultlib
 LDFLAGS_purgatory := -r $(PURGATORY_LDFLAGS) -T
 LDFLAGS_purgatory.chk := -e purgatory_start $(PURGATORY_LDFLAGS)
+# Purgatory doesn't export symbols, so disable symbol versioning.
+$(obj)/purgatory: skip_gendwarfksyms = 1
 $(obj)/purgatory: $(obj)/purgatory.lds $(PURGATORY_OBJS) FORCE
 		$(call if_changed,ld)
 
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 993708d11874..cfb4b57ff617 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -309,11 +309,11 @@ getasmexports =								\
      $(call getexportsymbols,EXPORT_SYMBOL(\1);) ; }
 
 ifdef CONFIG_GENDWARFKSYMS
-cmd_gensymtypes_S =							\
+cmd_gensymtypes_S = $(if $(skip_gendwarfksyms),,			\
 	$(getasmexports) |						\
 	$(CC) $(c_flags) -c -o $(@:.o=.gendwarfksyms.o) -xc -;		\
 	$(call getexportsymbols,\1) |					\
-	$(gendwarfksyms) $(@:.o=.gendwarfksyms.o)
+	$(gendwarfksyms) $(@:.o=.gendwarfksyms.o))
 else
 cmd_gensymtypes_S =							\
 	$(getasmexports) |						\