On Thu, Sep 29, 2022 at 3:25 AM Nathan Chancellor <nathan@xxxxxxxxxx> 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 > Tested-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx> > Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx> > --- > lib/Kconfig.debug | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index d3e5f36bb01e..19de03ead2ed 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -231,6 +231,9 @@ config DEBUG_INFO > in the "Debug information" choice below, indicating that debug > information will be generated for build targets. > > +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 > @@ -277,6 +280,10 @@ config DEBUG_INFO_DWARF5 > bool "Generate DWARF Version 5 debuginfo" > select DEBUG_INFO > depends on !CC_IS_CLANG || (CC_IS_CLANG && (AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502))) > + # 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 If you plan to patch both DWARF_TOOLCHAIN_DEFAULT and DWARF5, it will be cleaner to move this comment to AS_HAS_NON_CONST_LEB128. > + depends on !CC_IS_CLANG || AS_HAS_NON_CONST_LEB128 The condition "!CC_IS_CLANG" is repeated here. If you use the following patch as basic, https://lore.kernel.org/lkml/20221002181107.51286-2-masahiroy@xxxxxxxxxx/T/#u you can write the code like this: !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) Another big hammer solution is to give up Clang+GAS for CONFIG_DEBUG_INFO. If we go this way, this patch is unneeded, though. Thoughts? -- Best Regards Masahiro Yamada
