On Thu, Jan 14, 2021 at 12:27 AM Nick Desaulniers
[off-list ref] wrote:

Sedat,
Thanks for testing, and congrats on https://lwn.net/Articles/839772/.
I always appreciate you taking the time to help test my work, and
other Clang+Linux kernel patches!

Hi Nick,

cool, again in the top 15 :-).

I should ask Mr. Corbet for a LWN subscription.

On Wed, Jan 13, 2021 at 1:24 PM Sedat Dilek [off-list ref] wrote:

quoted

On Wed, Jan 13, 2021 at 1:32 AM Nick Desaulniers
[off-list ref] wrote:

quoted

--- a/Makefile
+++ b/Makefile

@@ -826,12 +826,16 @@ else
 DEBUG_CFLAGS   += -g
 endif

-ifneq ($(LLVM_IAS),1)
-KBUILD_AFLAGS  += -Wa,-gdwarf-2
+dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2
+dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
+DEBUG_CFLAGS   += -gdwarf-$(dwarf-version-y)

^ DEBUG_CFLAGS are set for everyone (all toolchains) if
CONFIG_DEBUG_INFO is defined.

quoted

quoted

+ifneq ($(dwarf-version-y)$(LLVM_IAS),21)

^ "If not using dwarf 2 and LLVM_IAS=1", ie. CONFIG_DEBUG_INFO_DWARF5
&& CONFIG_CC_IS_GCC

OK, I know DWARF v2 and LLVM_IAS=1 is broken.

Looks like DWARF v5 with GCC v10.2.1 and binutils v2.35.1 is currently
(here) no good choice.

quoted

quoted

+# Binutils 2.35+ required for -gdwarf-4+ support.
+dwarf-aflag    := $(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y))
+ifdef CONFIG_CC_IS_CLANG

^ "if clang"

quoted

quoted

+DEBUG_CFLAGS   += $(dwarf-aflag)
 endif

Why is that "ifdef CONFIG_CC_IS_CLANG"?

That's what Arvind requested on v2, IIUC:
https://lore.kernel.org/lkml/X8psgMuL4jMjP%2FOy@rani.riverdale.lan/ (local)

quoted

When I use GCC v10.2.1 DEBUG_CFLAGS are not set.

You should have -gdwarf-4 (and not -Wa,-gwarf-4) set for DEBUG_CFLAGS
when compiling with GCC and enabling CONFIG_DEBUG_INFO_DWARF4. Can you
please confirm? (Perhaps you may have accidentally disabled
CONFIG_DEBUG_INFO by rerunning `make defconfig`?)

$ egrep 'CC_IS_|LD_IS|BTF|DWARF'
config-5.11.0-rc3-5-amd64-gcc10-llvm11 | grep ^CONFIG
CONFIG_CC_IS_GCC=y
CONFIG_LD_IS_LLD=y
CONFIG_DEBUG_INFO_DWARF4=y
CONFIG_DEBUG_INFO_BTF=y
CONFIG_DEBUG_INFO_BTF_MODULES=y

$ grep '\-Wa,-gdwarf-4' build-log_5.11.0-rc3-5-amd64-gcc10-llvm11.txt
| wc -l
156