On Fri, Jan 29, 2021 at 12:57 PM Jakub Jelinek [off-list ref] wrote:

On Fri, Jan 29, 2021 at 12:48:11PM -0800, Nick Desaulniers wrote:

quoted

quoted

Should this be...?

KBUILD_AFLAGS += -Wa,-gdwarf-5

No; under the set of conditions Clang is compiling .c to .S with DWARF
v5 assembler directives. GAS will choke unless told -gdwarf-5 via
-Wa,-gdwarf-5 for .c source files, hence it is a C flag, not an A

Wasn't that fixed in GAS?
https://sourceware.org/bugzilla/show_bug.cgi?id=27195

diff --git a/Makefile b/Makefile
index bed8b3b180b8..de616e584706 100644
--- a/Makefile
+++ b/Makefile
@@ -835,17 +835,6 @@ dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
 dwarf-version-$(CONFIG_DEBUG_INFO_DWARF5) := 5
 DEBUG_CFLAGS   += -gdwarf-$(dwarf-version-y)

-# If using clang without the integrated assembler, we need to explicitly tell
-# GAS that we will be feeding it DWARF v5 assembler directives. Kconfig should
-# detect whether the version of GAS supports DWARF v5.
-ifdef CONFIG_CC_IS_CLANG
-ifneq ($(LLVM_IAS),1)
-ifeq ($(dwarf-version-y),5)
-DEBUG_CFLAGS   += -Wa,-gdwarf-5
-endif
-endif
-endif
-
 ifdef CONFIG_DEBUG_INFO_REDUCED
 DEBUG_CFLAGS   += $(call cc-option, -femit-struct-debug-baseonly) \
                   $(call cc-option,-fno-var-tracking)

$ make LLVM=1 -j72 defconfig
$ ./scripts/config -e DEBUG_INFO -e DEBUG_INFO_DWARF5
$ make LLVM=1 -j72
...
/tmp/init-d50d89.s: Assembler messages:
/tmp/init-d50d89.s:10: Error: file number less than one
/tmp/init-d50d89.s:11: Error: junk at end of line, first unrecognized
character is `m'

which is https://sourceware.org/bugzilla/show_bug.cgi?id=25611.

$ as --version | head -n1
GNU assembler (GNU Binutils for Debian) 2.35.1

Maybe GAS should not need to be told -gdwarf-5 to parse these?  Then
we would not need to pass -Wa,-gdwarf-5 via clang with
-no-integrated-as.
-- 
Thanks,
~Nick Desaulniers