From 0a6de78cff600cb991f2a1b7ed376935871796a0 Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Fri, 14 Oct 2022 13:42:11 -0700 Subject: [PATCH] lib/Kconfig.debug: Add check for non-constant .{s,u}leb128 support to DWARF5 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 Reviewed-by: Nick Desaulniers Signed-off-by: Masahiro Yamada --- lib/Kconfig.debug | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index db8d9271cabf5..5c1c635758951 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 -- 2.39.5