On Wed, Sep 28, 2022 at 02:13:47PM -0700, Nick Desaulniers wrote: > On Wed, Sep 28, 2022 at 11:25 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 > > + depends on !CC_IS_CLANG || AS_HAS_NON_CONST_LEB128 > > Reraising my concern from > https://github.com/ClangBuiltLinux/linux/issues/1719#issuecomment-1258678969 Sorry, I thought I addressed your concern with my comment right below it but I probably should have worded it better. > We've put a fair amount of work into getting CC=clang LLVM_IAS=0 to > work for DWARF v5 (both on the GNU binutils side, and Kbuild), I'd > hate to see that effectively knee-capped because of an issue in GNU > binutils that is only relevant for one architecture. Sure, that is a completely reasonable concern. However... > I'd concede support for ARCH=riscv, but not for all other > architectures, which this effectively does. No, it does not, CONFIG_AS_HAS_NON_CONST_LEB128 can still be enabled when GNU as supports this construct for a particular architecture; as far as I can tell, RISC-V is the only one that doesn't. See the tests with ARCH=arm64 and ARCH=x86_64 compared with ARCH=riscv below. $ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 LLVM_IAS=0 defconfig $ rg "CONFIG_AS_(IS|VERSION|HAS)" .config 9:CONFIG_AS_IS_GNU=y 10:CONFIG_AS_VERSION=23950 4750:CONFIG_AS_HAS_NON_CONST_LEB128=y $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- LLVM=1 LLVM_IAS=0 defconfig $ rg "CONFIG_AS_(IS|VERSION|HAS)" .config 9:CONFIG_AS_IS_GNU=y 10:CONFIG_AS_VERSION=23950 442:CONFIG_AS_HAS_LDAPR=y 443:CONFIG_AS_HAS_LSE_ATOMICS=y 451:CONFIG_AS_HAS_ARMV8_2=y 452:CONFIG_AS_HAS_SHA3=y 465:CONFIG_AS_HAS_PAC=y 466:CONFIG_AS_HAS_CFI_NEGATE_RA_STATE=y 473:CONFIG_AS_HAS_ARMV8_4=y 480:CONFIG_AS_HAS_ARMV8_5=y 9719:CONFIG_AS_HAS_NON_CONST_LEB128=y $ make -skj"$(nproc)" ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- LLVM=1 LLVM_IAS=0 defconfig $ rg "CONFIG_AS_(IS|VERSION|HAS)" .config 9:CONFIG_AS_IS_GNU=y 10:CONFIG_AS_VERSION=23950 Cheers, Nathan
