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Message-ID: <YztG0rb+cgf0IfPo@dev-arch.thelio-3990X> Date: Mon, 3 Oct 2022 13:32:18 -0700 From: Nathan Chancellor <nathan@...nel.org> To: Masahiro Yamada <masahiroy@...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 04, 2022 at 05:18:49AM +0900, Masahiro Yamada wrote: > 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. Ah, I figured that part was necessary because of the condition added to CONFIG_DEBUG_INFO_DWARF4 by commit 32ef9e5054ec ("Makefile.debug: re-enable debug info for .S files") but I see now that was because of some binutils behavior that you pointed out on Nick's v2 of that change, which I failed to pay attention to because I had already reviewed the change and did not read subsequent reviews/revisions as I should have, so my apologies. https://lore.kernel.org/CAK7LNATWDH01=ZKLnsxc0vcib1zGDbEq8jLQwhWP7HkkmSb_Mw@mail.gmail.com/ Regardless, I still think the duplication in these conditions is unfortunate and I would like to see it cleaned up in some way but I don't have a strong opinion on the matter. To the original change: Reviewed-by: Nathan Chancellor <nathan@...nel.org> Once these are applied to linux-kbuild, I will send a v2 of my RISC-V fix. > > 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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