Alexey reported that the fraction of unknown filename instances in
kallsyms grew from ~0.3% to ~10% recently; Bill and Greg tracked it down
to assembler defined symbols, which regressed as a result of:
commit b8a9092330da ("Kbuild: do not emit debug info for assembly with LLVM_IAS=1")
In that commit, I allude to restoring debug info for assembler defined
symbols in a follow up patch, but it seems I forgot to do so in
commit a66049e2cf0e ("Kbuild: make DWARF version a choice")
This patch does a few things:
1. Add -g to KBUILD_AFLAGS. This will instruct the compiler to instruct
the assembler to emit debug info. But this can cause an issue for
folks using a newer compiler but older assembler, because the
implicit default DWARF version changed from v4 to v5 in gcc-11 and
clang-14.
2. If the user is using CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT, use a
version check to explicitly set -Wa,-gdwarf-<version> for the
assembler. There's another problem with this; GAS only gained support
for explicit DWARF versions 3-5 in the 2.36 GNU binutils release.
3. Wrap -Wa,-gdwarf-<version> in as-option call to test whether the
assembler supports that explicit DWARF version.
Link: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=31bf18645d98b4d3d7357353be840e320649a67d
Fixes: b8a9092330da ("Kbuild: do not emit debug info for assembly with LLVM_IAS=1")
Reported-by: Alexey Alexandrov <aalexand@xxxxxxxxxx>
Reported-by: Bill Wendling <morbo@xxxxxxxxxx>
Reported-by: Greg Thelen <gthelen@xxxxxxxxxx>
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
---
Changes v1 -> v2:
* Use newly added compiler-specific macros, as per Bill.
scripts/Makefile.debug | 22 ++++++++++++++++++----
1 file changed, 18 insertions(+), 4 deletions(-)
diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug
index 9f39b0130551..46e88f0ca998 100644
--- a/scripts/Makefile.debug
+++ b/scripts/Makefile.debug
@@ -4,18 +4,32 @@ ifdef CONFIG_DEBUG_INFO_SPLIT
DEBUG_CFLAGS += -gsplit-dwarf
else
DEBUG_CFLAGS += -g
+KBUILD_AFLAGS += -g
endif
-ifndef CONFIG_AS_IS_LLVM
-KBUILD_AFLAGS += -Wa,-gdwarf-2
+ifdef CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
+# gcc-11+, clang-14+
+ifeq ($(call cc-min-version, 110000, 140000),y)
+dwarf-version-y := 5
+else
+dwarf-version-y := 4
endif
-
-ifndef CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
+else # !CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
dwarf-version-$(CONFIG_DEBUG_INFO_DWARF5) := 5
DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y)
endif
+# Binutils 2.35+ (or clang) required for -gdwarf-{4|5}.
+# https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=31bf18645d98b4d3d7357353be840e320649a67d
+ifneq ($(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y)),)
+KBUILD_AFLAGS += -Wa,-gdwarf-$(dwarf-version-y)
+else
+ifndef CONFIG_AS_IS_LLVM
+KBUILD_AFLAGS += -Wa,-gdwarf-2
+endif
+endif
+
ifdef CONFIG_DEBUG_INFO_REDUCED
DEBUG_CFLAGS += -fno-var-tracking
ifdef CONFIG_CC_IS_GCC
--
2.37.2.672.g94769d06f0-goog
