On Tue, Nov 24, 2020 at 9:28 AM Arvind Sankar <nivedita@xxxxxxxxxxxx> wrote: > > On Tue, Nov 03, 2020 at 04:53:43PM -0800, Nick Desaulniers wrote: > > DWARF v5 is the latest standard of the DWARF debug info format. > > > > Feature detection of DWARF5 is onerous, especially given that we've > > removed $(AS), so we must query $(CC) for DWARF5 assembler directive > > support. GNU `as` only recently gained support for specifying > > -gdwarf-5. > > With gcc, using -gdwarf-5 even without -Wa,--gdwarf-5 results in > considerably smaller debug info. gcc does not seem to generate the .file 0 > directive that causes older GNU as to barf. > > Should the assembler support check be restricted to CC_IS_CLANG? No, because if LLVM_IAS=1 then the assembler support need not be checked. > > > /* Stabs debugging sections. */ > > #define STABS_DEBUG \ > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > index 03c494eefabd..c5b54ba51060 100644 > > --- a/lib/Kconfig.debug > > +++ b/lib/Kconfig.debug > > @@ -274,6 +274,14 @@ config DEBUG_INFO_DWARF4 > > It makes the debug information larger, but it significantly > > improves the success of resolving variables in gdb on optimized code. > > > > +config DEBUG_INFO_DWARF5 > > + bool "Generate DWARF5 debuginfo" > > + depends on $(cc-option,-gdwarf-5) > > + depends on $(success,$(srctree)/scripts/test_dwarf5_support.sh $(CC) $(CLANG_FLAGS)) > > + help > > + Genereate dwarf5 debug info. Requires binutils 2.35+, gcc 5.1+, and > > + gdb 8.0+. > > + > > endchoice # "DWARF version" > > Perhaps this can be expanded with some description of the advantages of > dwarf5 over dwarf4? Will do. > > > > > config DEBUG_INFO_BTF > > diff --git a/scripts/test_dwarf5_support.sh b/scripts/test_dwarf5_support.sh > > new file mode 100755 > > index 000000000000..156ad5ec4274 > > --- /dev/null > > +++ b/scripts/test_dwarf5_support.sh > > @@ -0,0 +1,9 @@ > > +#!/bin/sh > > +# SPDX-License-Identifier: GPL-2.0 > > + > > +# Test that assembler accepts -gdwarf-5 and .file 0 directives, which were bugs > > +# in binutils < 2.35. > > +# https://sourceware.org/bugzilla/show_bug.cgi?id=25612 > > +# https://sourceware.org/bugzilla/show_bug.cgi?id=25614 > > +set -e > > +echo '.file 0 "filename"' | $* -Wa,-gdwarf-5 -c -x assembler -o /dev/null - > > This also actually needs --gdwarf-5 to really check the support for the > option, but older versions should error on the .file 0 in any case. Based on Jakub's feedback on the earlier thread https://lore.kernel.org/lkml/20201104121934.GT3788@tucnak/ it sounds like the dwarf version also needs to be dumped since GCC 5 < x < 7 accepts --gdwarf-5, but did not produce DWARF Version 5 debug info. -- Thanks, ~Nick Desaulniers
