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Message-ID: <CAK7LNASnp4DA9AADx4Nj9b_h6r5wfPFUaonfmOfaHaSizpyfgg@mail.gmail.com> Date: Tue, 4 Oct 2022 05:18:49 +0900 From: Masahiro Yamada <masahiroy@...nel.org> To: Nathan Chancellor <nathan@...nel.org> Cc: linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>, llvm@...ts.linux.dev Subject: Re: [PATCH 2/3] Kconfig.debug: add toolchain checks for DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT On Tue, Oct 4, 2022 at 2:10 AM Nathan Chancellor <nathan@...nel.org> wrote: > > On Mon, Oct 03, 2022 at 03:11:06AM +0900, Masahiro Yamada wrote: > > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT passes the -g option to the > > command line. The actual DWARF version is up to the toolchain. > > > > The combination of GCC and GAS works fine, and Clang with the integrated > > assembler is good too. > > > > The combination of Clang and GAS is a bit tricky, but at least, the > > default -g flag worked until LLVM 14 was released because Clang <=13 > > defaults to DWARF v4. > > > > Clang 14 switched to DWARF v5 by default. > > > > Now, CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT has the same issue as > > addressed by commit 98cd6f521f10 ("Kconfig: allow explicit opt in to > > DWARF v5"). > > > > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y for Clang >= 14 and > > GAS < 2.35 produces a ton of errors like follows: > > > > /tmp/main-c2741c.s: Assembler messages: > > /tmp/main-c2741c.s:109: Error: junk at end of line, first unrecognized character is `"' > > /tmp/main-c2741c.s:109: Error: file number less than one > > > > Add 'depends on' to check toolchains. > > > > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org> > > --- > > > > lib/Kconfig.debug | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > index f4b2165f24db..cc90414d492e 100644 > > --- a/lib/Kconfig.debug > > +++ b/lib/Kconfig.debug > > @@ -253,6 +253,7 @@ config DEBUG_INFO_NONE > > config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT > > bool "Rely on the toolchain's implicit default DWARF version" > > select DEBUG_INFO > > + depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502) > > help > > The implicit default version of DWARF debug info produced by a > > toolchain changes over time. > > -- > > 2.34.1 > > > > > > Could we do something like this instead? Bikeshed the configuration > names as much as you want but we are duplicating most of this > conditional in a few different places so it would be good to consolidate > those in my opinion. Even though the DWARF4 and DWARF5 conditions are > the same, they might diverge so I think it makes sense to keep them > separate. > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index cc90414d492e..8e34a639cd40 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -231,6 +231,17 @@ config DEBUG_INFO > in the "Debug information" choice below, indicating that debug > information will be generated for build targets. > > +config CC_AND_AS_SUPPORT_DWARF4 > + def_bool !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502) > + > +config CC_AND_AS_SUPPORT_DWARF5 > + def_bool !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502) > + > +config CC_AND_AS_SUPPORT_DWARF_DEFAULT > + bool > + default y if CC_AND_AS_SUPPORT_DWARF5 && (CLANG_VERSION >= 140000 || GCC_VERSION >= 110000) > + default y if CC_AND_AS_SUPPORT_DWARF4 && (CLANG_VERSION < 140000 || GCC_VERSION < 110000) No, this is an overkill. In my patch, you can enable DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT for the combination of: CC_IS_CLANG=y CLANG_VERSION < 140000 AS_IS_GNU=y AS_VERSION < 23502 But, your code disallows it. You are requiring binutils 2.35.2 for Clang+GAS, but it is not necessary. > choice > prompt "Debug information" > depends on DEBUG_KERNEL > @@ -253,7 +264,7 @@ config DEBUG_INFO_NONE > config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT > bool "Rely on the toolchain's implicit default DWARF version" > select DEBUG_INFO > - depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502) > + depends on CC_AND_AS_SUPPORT_DWARF_DEFAULT > help > The implicit default version of DWARF debug info produced by a > toolchain changes over time. > @@ -265,7 +276,7 @@ config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT > config DEBUG_INFO_DWARF4 > bool "Generate DWARF Version 4 debuginfo" > select DEBUG_INFO > - depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502) > + depends on CC_AND_AS_SUPPORT_DWARF4 > help > Generate DWARF v4 debug info. This requires gcc 4.5+, binutils 2.35.2 > if using clang without clang's integrated assembler, and gdb 7.0+. > @@ -277,7 +288,7 @@ config DEBUG_INFO_DWARF4 > config DEBUG_INFO_DWARF5 > bool "Generate DWARF Version 5 debuginfo" > select DEBUG_INFO > - depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502) > + depends on CC_AND_AS_SUPPORT_DWARF5 > help > Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc > 5.0+ accepts the -gdwarf-5 flag but only had partial support for some -- Best Regards Masahiro Yamada
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