diff mbox series

[v2] lib/Kconfig.debug: Add check for non-constant .{s,u}leb128 support to DWARF5

Message ID 20221014204210.383380-1-nathan@kernel.org
State New
Headers
Series [v2] lib/Kconfig.debug: Add check for non-constant .{s,u}leb128 support to DWARF5 |

Commit Message

Nathan Chancellor Oct. 14, 2022, 8:42 p.m. UTC 
  When building with a RISC-V kernel with DWARF5 debug info using clang
and the GNU assembler, several instances of the following error appear:

  /tmp/vgettimeofday-48aa35.s:2963: Error: non-constant .uleb128 is not supported

Dumping the .s file reveals these .uleb128 directives come from
.debug_loc and .debug_ranges:

  .Ldebug_loc0:
          .byte   4                               # DW_LLE_offset_pair
          .uleb128 .Lfunc_begin0-.Lfunc_begin0    #   starting offset
          .uleb128 .Ltmp1-.Lfunc_begin0           #   ending offset
          .byte   1                               # Loc expr size
          .byte   90                              # DW_OP_reg10
          .byte   0                               # DW_LLE_end_of_list

  .Ldebug_ranges0:
          .byte   4                               # DW_RLE_offset_pair
          .uleb128 .Ltmp6-.Lfunc_begin0           #   starting offset
          .uleb128 .Ltmp27-.Lfunc_begin0          #   ending offset
          .byte   4                               # DW_RLE_offset_pair
          .uleb128 .Ltmp28-.Lfunc_begin0          #   starting offset
          .uleb128 .Ltmp30-.Lfunc_begin0          #   ending offset
          .byte   0                               # DW_RLE_end_of_list

There is an outstanding binutils issue to support a non-constant operand
to .sleb128 and .uleb128 in GAS for RISC-V but there does not appear to
be any movement on it, due to concerns over how it would work with
linker relaxation.

To avoid these build errors, prevent DWARF5 from being selected when
using clang and an assembler that does not have support for these symbol
deltas, which can be easily checked in Kconfig with as-instr plus the
small test program from the dwz test suite from the binutils issue.

Link: https://sourceware.org/bugzilla/show_bug.cgi?id=27215
Link: https://github.com/ClangBuiltLinux/linux/issues/1719
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---

v2:
    - Rebase on commit bb1435f3f575 ("Kconfig.debug: add toolchain
      checks for DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT") from the kbuild
      tree.
    - Limit CONFIG_AS_HAS_NON_CONST_LEB128 dependency to GNU as. There
      is no point to applying this dependency to the integrated
      assembler because it will always pass.
    - Apply the CONFIG_AS_HAS_NON_CONST_LEB128 dependency to
      CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT as well, due to the
      aforementioned kbuild change.
    - Move comment block to above CONFIG_AS_HAS_NON_CONST_LEB128, as the
      configuration is now used in two places.
    - Drop Conor's tested by, as the patch is different enough to
      potentially require new testing.

v1: https://lore.kernel.org/20220928182523.3105953-1-nathan@kernel.org/

 lib/Kconfig.debug | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)


base-commit: bb1435f3f575b5213eaf27434efa3971f51c01de

Comments

Nick Desaulniers Oct. 14, 2022, 9:51 p.m. UTC | #1 
On Fri, Oct 14, 2022 at 1:48 PM Nathan Chancellor <nathan@kernel.org> wrote:
>
> When building with a RISC-V kernel with DWARF5 debug info using clang
> and the GNU assembler, several instances of the following error appear:
>
>   /tmp/vgettimeofday-48aa35.s:2963: Error: non-constant .uleb128 is not supported
>
> Dumping the .s file reveals these .uleb128 directives come from
> .debug_loc and .debug_ranges:
>
>   .Ldebug_loc0:
>           .byte   4                               # DW_LLE_offset_pair
>           .uleb128 .Lfunc_begin0-.Lfunc_begin0    #   starting offset
>           .uleb128 .Ltmp1-.Lfunc_begin0           #   ending offset
>           .byte   1                               # Loc expr size
>           .byte   90                              # DW_OP_reg10
>           .byte   0                               # DW_LLE_end_of_list
>
>   .Ldebug_ranges0:
>           .byte   4                               # DW_RLE_offset_pair
>           .uleb128 .Ltmp6-.Lfunc_begin0           #   starting offset
>           .uleb128 .Ltmp27-.Lfunc_begin0          #   ending offset
>           .byte   4                               # DW_RLE_offset_pair
>           .uleb128 .Ltmp28-.Lfunc_begin0          #   starting offset
>           .uleb128 .Ltmp30-.Lfunc_begin0          #   ending offset
>           .byte   0                               # DW_RLE_end_of_list
>
> There is an outstanding binutils issue to support a non-constant operand
> to .sleb128 and .uleb128 in GAS for RISC-V but there does not appear to
> be any movement on it, due to concerns over how it would work with
> linker relaxation.
>
> To avoid these build errors, prevent DWARF5 from being selected when
> using clang and an assembler that does not have support for these symbol
> deltas, which can be easily checked in Kconfig with as-instr plus the
> small test program from the dwz test suite from the binutils issue.
>
> Link: https://sourceware.org/bugzilla/show_bug.cgi?id=27215
> Link: https://github.com/ClangBuiltLinux/linux/issues/1719
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Thanks for keeping these LLVM_IAS=0 builds alive a little longer.  My
hope is the GNU binutils can relax their requirement for debug info
sections to improve support for DWARF v5.

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>


> ---
>
> v2:
>     - Rebase on commit bb1435f3f575 ("Kconfig.debug: add toolchain
>       checks for DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT") from the kbuild
>       tree.
>     - Limit CONFIG_AS_HAS_NON_CONST_LEB128 dependency to GNU as. There
>       is no point to applying this dependency to the integrated
>       assembler because it will always pass.
>     - Apply the CONFIG_AS_HAS_NON_CONST_LEB128 dependency to
>       CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT as well, due to the
>       aforementioned kbuild change.
>     - Move comment block to above CONFIG_AS_HAS_NON_CONST_LEB128, as the
>       configuration is now used in two places.
>     - Drop Conor's tested by, as the patch is different enough to
>       potentially require new testing.
>
> v1: https://lore.kernel.org/20220928182523.3105953-1-nathan@kernel.org/
>
>  lib/Kconfig.debug | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index db8d9271cabf..5c1c63575895 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -231,6 +231,11 @@ config DEBUG_INFO
>           in the "Debug information" choice below, indicating that debug
>           information will be generated for build targets.
>
> +# Clang is known to generate .{s,u}leb128 with symbol deltas with DWARF5, which
> +# some targets may not support: https://sourceware.org/bugzilla/show_bug.cgi?id=27215
> +config AS_HAS_NON_CONST_LEB128
> +       def_bool $(as-instr,.uleb128 .Lexpr_end4 - .Lexpr_start3\n.Lexpr_start3:\n.Lexpr_end4:)
> +
>  choice
>         prompt "Debug information"
>         depends on DEBUG_KERNEL
> @@ -253,7 +258,7 @@ 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_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128)
>         help
>           The implicit default version of DWARF debug info produced by a
>           toolchain changes over time.
> @@ -277,7 +282,7 @@ 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_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128)
>         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
>
> base-commit: bb1435f3f575b5213eaf27434efa3971f51c01de
> --
> 2.38.0
>


--
Thanks,
~Nick Desaulniers
Masahiro Yamada Oct. 16, 2022, 6 p.m. UTC | #2 
On Sat, Oct 15, 2022 at 6:52 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Fri, Oct 14, 2022 at 1:48 PM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > When building with a RISC-V kernel with DWARF5 debug info using clang
> > and the GNU assembler, several instances of the following error appear:
> >
> >   /tmp/vgettimeofday-48aa35.s:2963: Error: non-constant .uleb128 is not supported
> >
> > Dumping the .s file reveals these .uleb128 directives come from
> > .debug_loc and .debug_ranges:
> >
> >   .Ldebug_loc0:
> >           .byte   4                               # DW_LLE_offset_pair
> >           .uleb128 .Lfunc_begin0-.Lfunc_begin0    #   starting offset
> >           .uleb128 .Ltmp1-.Lfunc_begin0           #   ending offset
> >           .byte   1                               # Loc expr size
> >           .byte   90                              # DW_OP_reg10
> >           .byte   0                               # DW_LLE_end_of_list
> >
> >   .Ldebug_ranges0:
> >           .byte   4                               # DW_RLE_offset_pair
> >           .uleb128 .Ltmp6-.Lfunc_begin0           #   starting offset
> >           .uleb128 .Ltmp27-.Lfunc_begin0          #   ending offset
> >           .byte   4                               # DW_RLE_offset_pair
> >           .uleb128 .Ltmp28-.Lfunc_begin0          #   starting offset
> >           .uleb128 .Ltmp30-.Lfunc_begin0          #   ending offset
> >           .byte   0                               # DW_RLE_end_of_list
> >
> > There is an outstanding binutils issue to support a non-constant operand
> > to .sleb128 and .uleb128 in GAS for RISC-V but there does not appear to
> > be any movement on it, due to concerns over how it would work with
> > linker relaxation.
> >
> > To avoid these build errors, prevent DWARF5 from being selected when
> > using clang and an assembler that does not have support for these symbol
> > deltas, which can be easily checked in Kconfig with as-instr plus the
> > small test program from the dwz test suite from the binutils issue.
> >
> > Link: https://sourceware.org/bugzilla/show_bug.cgi?id=27215
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1719
> > Signed-off-by: Nathan Chancellor <nathan@kernel.org>
>
> Thanks for keeping these LLVM_IAS=0 builds alive a little longer.  My
> hope is the GNU binutils can relax their requirement for debug info
> sections to improve support for DWARF v5.
>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>


Applied to linux-kbuild.
Thanks.



> > ---
> >
> > v2:
> >     - Rebase on commit bb1435f3f575 ("Kconfig.debug: add toolchain
> >       checks for DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT") from the kbuild
> >       tree.
> >     - Limit CONFIG_AS_HAS_NON_CONST_LEB128 dependency to GNU as. There
> >       is no point to applying this dependency to the integrated
> >       assembler because it will always pass.
> >     - Apply the CONFIG_AS_HAS_NON_CONST_LEB128 dependency to
> >       CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT as well, due to the
> >       aforementioned kbuild change.
> >     - Move comment block to above CONFIG_AS_HAS_NON_CONST_LEB128, as the
> >       configuration is now used in two places.
> >     - Drop Conor's tested by, as the patch is different enough to
> >       potentially require new testing.
> >
> > v1: https://lore.kernel.org/20220928182523.3105953-1-nathan@kernel.org/
> >
> >  lib/Kconfig.debug | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index db8d9271cabf..5c1c63575895 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -231,6 +231,11 @@ config DEBUG_INFO
> >           in the "Debug information" choice below, indicating that debug
> >           information will be generated for build targets.
> >
> > +# Clang is known to generate .{s,u}leb128 with symbol deltas with DWARF5, which
> > +# some targets may not support: https://sourceware.org/bugzilla/show_bug.cgi?id=27215
> > +config AS_HAS_NON_CONST_LEB128
> > +       def_bool $(as-instr,.uleb128 .Lexpr_end4 - .Lexpr_start3\n.Lexpr_start3:\n.Lexpr_end4:)
> > +
> >  choice
> >         prompt "Debug information"
> >         depends on DEBUG_KERNEL
> > @@ -253,7 +258,7 @@ 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_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128)
> >         help
> >           The implicit default version of DWARF debug info produced by a
> >           toolchain changes over time.
> > @@ -277,7 +282,7 @@ 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_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128)
> >         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
> >
> > base-commit: bb1435f3f575b5213eaf27434efa3971f51c01de
> > --
> > 2.38.0
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers



--
Best Regards
Masahiro Yamada
Sedat Dilek Oct. 16, 2022, 6:10 p.m. UTC | #3 
On Sun, Oct 16, 2022 at 8:04 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Sat, Oct 15, 2022 at 6:52 AM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > On Fri, Oct 14, 2022 at 1:48 PM Nathan Chancellor <nathan@kernel.org> wrote:
> > >
> > > When building with a RISC-V kernel with DWARF5 debug info using clang
> > > and the GNU assembler, several instances of the following error appear:
> > >
> > >   /tmp/vgettimeofday-48aa35.s:2963: Error: non-constant .uleb128 is not supported
> > >
> > > Dumping the .s file reveals these .uleb128 directives come from
> > > .debug_loc and .debug_ranges:
> > >
> > >   .Ldebug_loc0:
> > >           .byte   4                               # DW_LLE_offset_pair
> > >           .uleb128 .Lfunc_begin0-.Lfunc_begin0    #   starting offset
> > >           .uleb128 .Ltmp1-.Lfunc_begin0           #   ending offset
> > >           .byte   1                               # Loc expr size
> > >           .byte   90                              # DW_OP_reg10
> > >           .byte   0                               # DW_LLE_end_of_list
> > >
> > >   .Ldebug_ranges0:
> > >           .byte   4                               # DW_RLE_offset_pair
> > >           .uleb128 .Ltmp6-.Lfunc_begin0           #   starting offset
> > >           .uleb128 .Ltmp27-.Lfunc_begin0          #   ending offset
> > >           .byte   4                               # DW_RLE_offset_pair
> > >           .uleb128 .Ltmp28-.Lfunc_begin0          #   starting offset
> > >           .uleb128 .Ltmp30-.Lfunc_begin0          #   ending offset
> > >           .byte   0                               # DW_RLE_end_of_list
> > >
> > > There is an outstanding binutils issue to support a non-constant operand
> > > to .sleb128 and .uleb128 in GAS for RISC-V but there does not appear to
> > > be any movement on it, due to concerns over how it would work with
> > > linker relaxation.
> > >
> > > To avoid these build errors, prevent DWARF5 from being selected when
> > > using clang and an assembler that does not have support for these symbol
> > > deltas, which can be easily checked in Kconfig with as-instr plus the
> > > small test program from the dwz test suite from the binutils issue.
> > >
> > > Link: https://sourceware.org/bugzilla/show_bug.cgi?id=27215
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/1719
> > > Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> >
> > Thanks for keeping these LLVM_IAS=0 builds alive a little longer.  My
> > hope is the GNU binutils can relax their requirement for debug info
> > sections to improve support for DWARF v5.
> >
> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>
>
> Applied to linux-kbuild.
> Thanks.
>

[1] says:

"This looks good to me! Feel free to submit with a:
Tested-by: Conor Dooley <conor.dooley@microchip.com>"

-sed@-

[1] https://github.com/ClangBuiltLinux/linux/issues/1719#issuecomment-1261158627

>
>
> > > ---
> > >
> > > v2:
> > >     - Rebase on commit bb1435f3f575 ("Kconfig.debug: add toolchain
> > >       checks for DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT") from the kbuild
> > >       tree.
> > >     - Limit CONFIG_AS_HAS_NON_CONST_LEB128 dependency to GNU as. There
> > >       is no point to applying this dependency to the integrated
> > >       assembler because it will always pass.
> > >     - Apply the CONFIG_AS_HAS_NON_CONST_LEB128 dependency to
> > >       CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT as well, due to the
> > >       aforementioned kbuild change.
> > >     - Move comment block to above CONFIG_AS_HAS_NON_CONST_LEB128, as the
> > >       configuration is now used in two places.
> > >     - Drop Conor's tested by, as the patch is different enough to
> > >       potentially require new testing.
> > >
> > > v1: https://lore.kernel.org/20220928182523.3105953-1-nathan@kernel.org/
> > >
> > >  lib/Kconfig.debug | 9 +++++++--
> > >  1 file changed, 7 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > > index db8d9271cabf..5c1c63575895 100644
> > > --- a/lib/Kconfig.debug
> > > +++ b/lib/Kconfig.debug
> > > @@ -231,6 +231,11 @@ config DEBUG_INFO
> > >           in the "Debug information" choice below, indicating that debug
> > >           information will be generated for build targets.
> > >
> > > +# Clang is known to generate .{s,u}leb128 with symbol deltas with DWARF5, which
> > > +# some targets may not support: https://sourceware.org/bugzilla/show_bug.cgi?id=27215
> > > +config AS_HAS_NON_CONST_LEB128
> > > +       def_bool $(as-instr,.uleb128 .Lexpr_end4 - .Lexpr_start3\n.Lexpr_start3:\n.Lexpr_end4:)
> > > +
> > >  choice
> > >         prompt "Debug information"
> > >         depends on DEBUG_KERNEL
> > > @@ -253,7 +258,7 @@ 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_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128)
> > >         help
> > >           The implicit default version of DWARF debug info produced by a
> > >           toolchain changes over time.
> > > @@ -277,7 +282,7 @@ 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_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128)
> > >         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
> > >
> > > base-commit: bb1435f3f575b5213eaf27434efa3971f51c01de
> > > --
> > > 2.38.0
> > >
> >
> >
> > --
> > Thanks,
> > ~Nick Desaulniers
>
>
>
> --
> Best Regards
> Masahiro Yamada
Conor Dooley Oct. 16, 2022, 6:20 p.m. UTC | #4 
On Sun, Oct 16, 2022 at 08:10:30PM +0200, Sedat Dilek wrote:
> On Sun, Oct 16, 2022 at 8:04 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > On Sat, Oct 15, 2022 at 6:52 AM Nick Desaulniers
> > <ndesaulniers@google.com> wrote:
> > >
> > > On Fri, Oct 14, 2022 at 1:48 PM Nathan Chancellor <nathan@kernel.org> wrote:
> > > >
> > > > When building with a RISC-V kernel with DWARF5 debug info using clang
> > > > and the GNU assembler, several instances of the following error appear:
> > > >
> > > >   /tmp/vgettimeofday-48aa35.s:2963: Error: non-constant .uleb128 is not supported
> > > >
> > > > Dumping the .s file reveals these .uleb128 directives come from
> > > > .debug_loc and .debug_ranges:
> > > >
> > > >   .Ldebug_loc0:
> > > >           .byte   4                               # DW_LLE_offset_pair
> > > >           .uleb128 .Lfunc_begin0-.Lfunc_begin0    #   starting offset
> > > >           .uleb128 .Ltmp1-.Lfunc_begin0           #   ending offset
> > > >           .byte   1                               # Loc expr size
> > > >           .byte   90                              # DW_OP_reg10
> > > >           .byte   0                               # DW_LLE_end_of_list
> > > >
> > > >   .Ldebug_ranges0:
> > > >           .byte   4                               # DW_RLE_offset_pair
> > > >           .uleb128 .Ltmp6-.Lfunc_begin0           #   starting offset
> > > >           .uleb128 .Ltmp27-.Lfunc_begin0          #   ending offset
> > > >           .byte   4                               # DW_RLE_offset_pair
> > > >           .uleb128 .Ltmp28-.Lfunc_begin0          #   starting offset
> > > >           .uleb128 .Ltmp30-.Lfunc_begin0          #   ending offset
> > > >           .byte   0                               # DW_RLE_end_of_list
> > > >
> > > > There is an outstanding binutils issue to support a non-constant operand
> > > > to .sleb128 and .uleb128 in GAS for RISC-V but there does not appear to
> > > > be any movement on it, due to concerns over how it would work with
> > > > linker relaxation.
> > > >
> > > > To avoid these build errors, prevent DWARF5 from being selected when
> > > > using clang and an assembler that does not have support for these symbol
> > > > deltas, which can be easily checked in Kconfig with as-instr plus the
> > > > small test program from the dwz test suite from the binutils issue.
> > > >
> > > > Link: https://sourceware.org/bugzilla/show_bug.cgi?id=27215
> > > > Link: https://github.com/ClangBuiltLinux/linux/issues/1719
> > > > Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> > >
> > > Thanks for keeping these LLVM_IAS=0 builds alive a little longer.  My
> > > hope is the GNU binutils can relax their requirement for debug info
> > > sections to improve support for DWARF v5.
> > >
> > > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> >
> >
> > Applied to linux-kbuild.
> > Thanks.
> >
> 
> [1] says:
> 
> "This looks good to me! Feel free to submit with a:
> Tested-by: Conor Dooley <conor.dooley@microchip.com>"

Hey Sedat,

I actually didn't take a proper look at the v2 at all... I didn't realise
that Nathan dropped by T-b for v2 since he'd changed the patch enough to
feel that he should.

I'm not too worried about the removed T-b (espcially since Linus has
just merged Masahiro's PR containing this change).

Thanks though!
Conor.

> 
> -sed@-
> 
> [1] https://github.com/ClangBuiltLinux/linux/issues/1719#issuecomment-1261158627
> 
> >
> >
> > > > ---
> > > >
> > > > v2:
> > > >     - Rebase on commit bb1435f3f575 ("Kconfig.debug: add toolchain
> > > >       checks for DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT") from the kbuild
> > > >       tree.
> > > >     - Limit CONFIG_AS_HAS_NON_CONST_LEB128 dependency to GNU as. There
> > > >       is no point to applying this dependency to the integrated
> > > >       assembler because it will always pass.
> > > >     - Apply the CONFIG_AS_HAS_NON_CONST_LEB128 dependency to
> > > >       CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT as well, due to the
> > > >       aforementioned kbuild change.
> > > >     - Move comment block to above CONFIG_AS_HAS_NON_CONST_LEB128, as the
> > > >       configuration is now used in two places.
> > > >     - Drop Conor's tested by, as the patch is different enough to
> > > >       potentially require new testing.
> > > >
> > > > v1: https://lore.kernel.org/20220928182523.3105953-1-nathan@kernel.org/
> > > >
> > > >  lib/Kconfig.debug | 9 +++++++--
> > > >  1 file changed, 7 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > > > index db8d9271cabf..5c1c63575895 100644
> > > > --- a/lib/Kconfig.debug
> > > > +++ b/lib/Kconfig.debug
> > > > @@ -231,6 +231,11 @@ config DEBUG_INFO
> > > >           in the "Debug information" choice below, indicating that debug
> > > >           information will be generated for build targets.
> > > >
> > > > +# Clang is known to generate .{s,u}leb128 with symbol deltas with DWARF5, which
> > > > +# some targets may not support: https://sourceware.org/bugzilla/show_bug.cgi?id=27215
> > > > +config AS_HAS_NON_CONST_LEB128
> > > > +       def_bool $(as-instr,.uleb128 .Lexpr_end4 - .Lexpr_start3\n.Lexpr_start3:\n.Lexpr_end4:)
> > > > +
> > > >  choice
> > > >         prompt "Debug information"
> > > >         depends on DEBUG_KERNEL
> > > > @@ -253,7 +258,7 @@ 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_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128)
> > > >         help
> > > >           The implicit default version of DWARF debug info produced by a
> > > >           toolchain changes over time.
> > > > @@ -277,7 +282,7 @@ 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_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128)
> > > >         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
> > > >
> > > > base-commit: bb1435f3f575b5213eaf27434efa3971f51c01de
> > > > --
> > > > 2.38.0
> > > >
> > >
> > >
> > > --
> > > Thanks,
> > > ~Nick Desaulniers
> >
> >
> >
> > --
> > Best Regards
> > Masahiro Yamada
Sedat Dilek Oct. 16, 2022, 6:22 p.m. UTC | #5 
On Sun, Oct 16, 2022 at 8:20 PM Conor Dooley <conor@kernel.org> wrote:
>
> On Sun, Oct 16, 2022 at 08:10:30PM +0200, Sedat Dilek wrote:
> > On Sun, Oct 16, 2022 at 8:04 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > >
> > > On Sat, Oct 15, 2022 at 6:52 AM Nick Desaulniers
> > > <ndesaulniers@google.com> wrote:
> > > >
> > > > On Fri, Oct 14, 2022 at 1:48 PM Nathan Chancellor <nathan@kernel.org> wrote:
> > > > >
> > > > > When building with a RISC-V kernel with DWARF5 debug info using clang
> > > > > and the GNU assembler, several instances of the following error appear:
> > > > >
> > > > >   /tmp/vgettimeofday-48aa35.s:2963: Error: non-constant .uleb128 is not supported
> > > > >
> > > > > Dumping the .s file reveals these .uleb128 directives come from
> > > > > .debug_loc and .debug_ranges:
> > > > >
> > > > >   .Ldebug_loc0:
> > > > >           .byte   4                               # DW_LLE_offset_pair
> > > > >           .uleb128 .Lfunc_begin0-.Lfunc_begin0    #   starting offset
> > > > >           .uleb128 .Ltmp1-.Lfunc_begin0           #   ending offset
> > > > >           .byte   1                               # Loc expr size
> > > > >           .byte   90                              # DW_OP_reg10
> > > > >           .byte   0                               # DW_LLE_end_of_list
> > > > >
> > > > >   .Ldebug_ranges0:
> > > > >           .byte   4                               # DW_RLE_offset_pair
> > > > >           .uleb128 .Ltmp6-.Lfunc_begin0           #   starting offset
> > > > >           .uleb128 .Ltmp27-.Lfunc_begin0          #   ending offset
> > > > >           .byte   4                               # DW_RLE_offset_pair
> > > > >           .uleb128 .Ltmp28-.Lfunc_begin0          #   starting offset
> > > > >           .uleb128 .Ltmp30-.Lfunc_begin0          #   ending offset
> > > > >           .byte   0                               # DW_RLE_end_of_list
> > > > >
> > > > > There is an outstanding binutils issue to support a non-constant operand
> > > > > to .sleb128 and .uleb128 in GAS for RISC-V but there does not appear to
> > > > > be any movement on it, due to concerns over how it would work with
> > > > > linker relaxation.
> > > > >
> > > > > To avoid these build errors, prevent DWARF5 from being selected when
> > > > > using clang and an assembler that does not have support for these symbol
> > > > > deltas, which can be easily checked in Kconfig with as-instr plus the
> > > > > small test program from the dwz test suite from the binutils issue.
> > > > >
> > > > > Link: https://sourceware.org/bugzilla/show_bug.cgi?id=27215
> > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/1719
> > > > > Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> > > >
> > > > Thanks for keeping these LLVM_IAS=0 builds alive a little longer.  My
> > > > hope is the GNU binutils can relax their requirement for debug info
> > > > sections to improve support for DWARF v5.
> > > >
> > > > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> > >
> > >
> > > Applied to linux-kbuild.
> > > Thanks.
> > >
> >
> > [1] says:
> >
> > "This looks good to me! Feel free to submit with a:
> > Tested-by: Conor Dooley <conor.dooley@microchip.com>"
>
> Hey Sedat,
>
> I actually didn't take a proper look at the v2 at all... I didn't realise
> that Nathan dropped by T-b for v2 since he'd changed the patch enough to
> feel that he should.
>
> I'm not too worried about the removed T-b (espcially since Linus has
> just merged Masahiro's PR containing this change).
>
> Thanks though!
> Conor.
>

Yes, just saw the update on
https://github.com/torvalds/linux/commits/master first.

-Sedat-

> >
> > -sed@-
> >
> > [1] https://github.com/ClangBuiltLinux/linux/issues/1719#issuecomment-1261158627
> >
> > >
> > >
> > > > > ---
> > > > >
> > > > > v2:
> > > > >     - Rebase on commit bb1435f3f575 ("Kconfig.debug: add toolchain
> > > > >       checks for DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT") from the kbuild
> > > > >       tree.
> > > > >     - Limit CONFIG_AS_HAS_NON_CONST_LEB128 dependency to GNU as. There
> > > > >       is no point to applying this dependency to the integrated
> > > > >       assembler because it will always pass.
> > > > >     - Apply the CONFIG_AS_HAS_NON_CONST_LEB128 dependency to
> > > > >       CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT as well, due to the
> > > > >       aforementioned kbuild change.
> > > > >     - Move comment block to above CONFIG_AS_HAS_NON_CONST_LEB128, as the
> > > > >       configuration is now used in two places.
> > > > >     - Drop Conor's tested by, as the patch is different enough to
> > > > >       potentially require new testing.
> > > > >
> > > > > v1: https://lore.kernel.org/20220928182523.3105953-1-nathan@kernel.org/
> > > > >
> > > > >  lib/Kconfig.debug | 9 +++++++--
> > > > >  1 file changed, 7 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > > > > index db8d9271cabf..5c1c63575895 100644
> > > > > --- a/lib/Kconfig.debug
> > > > > +++ b/lib/Kconfig.debug
> > > > > @@ -231,6 +231,11 @@ config DEBUG_INFO
> > > > >           in the "Debug information" choice below, indicating that debug
> > > > >           information will be generated for build targets.
> > > > >
> > > > > +# Clang is known to generate .{s,u}leb128 with symbol deltas with DWARF5, which
> > > > > +# some targets may not support: https://sourceware.org/bugzilla/show_bug.cgi?id=27215
> > > > > +config AS_HAS_NON_CONST_LEB128
> > > > > +       def_bool $(as-instr,.uleb128 .Lexpr_end4 - .Lexpr_start3\n.Lexpr_start3:\n.Lexpr_end4:)
> > > > > +
> > > > >  choice
> > > > >         prompt "Debug information"
> > > > >         depends on DEBUG_KERNEL
> > > > > @@ -253,7 +258,7 @@ 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_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128)
> > > > >         help
> > > > >           The implicit default version of DWARF debug info produced by a
> > > > >           toolchain changes over time.
> > > > > @@ -277,7 +282,7 @@ 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_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128)
> > > > >         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
> > > > >
> > > > > base-commit: bb1435f3f575b5213eaf27434efa3971f51c01de
> > > > > --
> > > > > 2.38.0
> > > > >
> > > >
> > > >
> > > > --
> > > > Thanks,
> > > > ~Nick Desaulniers
> > >
> > >
> > >
> > > --
> > > Best Regards
> > > Masahiro Yamada
Andrew Morton Oct. 17, 2022, 12:28 a.m. UTC | #6 
On Fri, 14 Oct 2022 13:42:11 -0700 Nathan Chancellor <nathan@kernel.org> wrote:

> When building with a RISC-V kernel with DWARF5 debug info using clang
> and the GNU assembler, several instances of the following error appear:
> 
>   /tmp/vgettimeofday-48aa35.s:2963: Error: non-constant .uleb128 is not supported

hm, which kernels want this?

I could merge it for 6.1, which seems suitable.  If we want it
backported into earlier kernels then a Fixes: would be nice, to prevent
it from being ported back further than necessary.
Nathan Chancellor Oct. 17, 2022, 12:41 a.m. UTC | #7 
Hi Andrew,

On Sun, Oct 16, 2022 at 05:28:15PM -0700, Andrew Morton wrote:
> On Fri, 14 Oct 2022 13:42:11 -0700 Nathan Chancellor <nathan@kernel.org> wrote:
> 
> > When building with a RISC-V kernel with DWARF5 debug info using clang
> > and the GNU assembler, several instances of the following error appear:
> > 
> >   /tmp/vgettimeofday-48aa35.s:2963: Error: non-constant .uleb128 is not supported
> 
> hm, which kernels want this?
> 
> I could merge it for 6.1, which seems suitable.  If we want it
> backported into earlier kernels then a Fixes: would be nice, to prevent
> it from being ported back further than necessary.

Masahiro took this for 6.1 via the kbuild tree, it is now in mainline as
commit 0a6de78cff60 ("lib/Kconfig.debug: Add check for non-constant
.{s,u}leb128 support to DWARF5"). It does need to go to stable but it
needs a few prerequisite changes to cover all cases and I did not want
to try and describe those dependencies in the patch itself. I should be
able to handle the backports manually tomorrow.

Cheers,
Nathan
diff mbox series

Patch

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index db8d9271cabf..5c1c63575895 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -231,6 +231,11 @@  config DEBUG_INFO
 	  in the "Debug information" choice below, indicating that debug
 	  information will be generated for build targets.
 
+# Clang is known to generate .{s,u}leb128 with symbol deltas with DWARF5, which
+# some targets may not support: https://sourceware.org/bugzilla/show_bug.cgi?id=27215
+config AS_HAS_NON_CONST_LEB128
+	def_bool $(as-instr,.uleb128 .Lexpr_end4 - .Lexpr_start3\n.Lexpr_start3:\n.Lexpr_end4:)
+
 choice
 	prompt "Debug information"
 	depends on DEBUG_KERNEL
@@ -253,7 +258,7 @@  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_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128)
 	help
 	  The implicit default version of DWARF debug info produced by a
 	  toolchain changes over time.
@@ -277,7 +282,7 @@  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_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128)
 	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