From ae84ff9a14a5a8d36a329a30626800155782e617 Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Tue, 5 Dec 2023 16:53:51 -0700 Subject: riscv: Restrict DWARF5 when building with LLVM to known working versions LLVM prior to 18.0.0 would generate incorrect debug info for DWARF5 due to linker relaxation, which was worked around in clang by defaulting RISC-V to DWARF4 [1]. Unfortunately, this workaround does not work for the kernel because the DWARF version can be independently changed from the default in Kconfig. Do not allow DWARF5 to be selected for RISC-V when using linker relaxation (ld.lld >= 15.0.0) and a version of LLVM that does not have the fixes (the integrated assembler [2] and ld.lld [3] < 18.0.0) necessary to generate the correct debug info. Link: https://github.com/llvm/llvm-project/commit/bbc0f99f3bc96f1db16f649fc21dd18e5b0918f6 [1] Link: https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a [2] Link: https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77 [3] Signed-off-by: Nathan Chancellor Reviewed-by: Fangrui Song Link: https://lore.kernel.org/r/20231205-riscv-restrict-dwarf5-llvm-v2-2-aedf00a382ac@kernel.org Signed-off-by: Palmer Dabbelt --- lib/Kconfig.debug | 1 + 1 file changed, 1 insertion(+) (limited to 'lib') diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index cc7d53d9dc01..a0ebce05a368 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -282,6 +282,7 @@ config DEBUG_INFO_DWARF4 config DEBUG_INFO_DWARF5 bool "Generate DWARF Version 5 debuginfo" select DEBUG_INFO + depends on !ARCH_HAS_BROKEN_DWARF5 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 -- cgit v1.2.3 From a4426641f00cd2c293c91e881ab31faaf76b20fb Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Tue, 5 Dec 2023 16:53:52 -0700 Subject: lib/Kconfig.debug: Update AS_HAS_NON_CONST_LEB128 comment and name Fangrui noted that the comment around CONFIG_AS_HAS_NON_CONST_LEB128 could be made more accurate because explicit .sleb128 directives are not emitted, only .uleb128 directives are. Rename the symbol to CONFIG_AS_HAS_NON_CONST_ULEB128 as a result. Further clarifications include replacing "symbol deltas" with the more accurate "label differences", noting that this issue has been resolved in newer binutils (2.41+), and it only occurs when a port uses RISC-V style linker relaxation. Suggested-by: Fangrui Song Signed-off-by: Nathan Chancellor Reviewed-by: Charlie Jenkins Link: https://lore.kernel.org/r/20231205-riscv-restrict-dwarf5-llvm-v2-3-aedf00a382ac@kernel.org Signed-off-by: Palmer Dabbelt --- lib/Kconfig.debug | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) (limited to 'lib') diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index a0ebce05a368..76c2cc697573 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -231,9 +231,10 @@ 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 +# Clang generates .uleb128 with label differences for DWARF v5, a feature that +# older binutils ports do not support when utilizing RISC-V style linker +# relaxation: https://sourceware.org/bugzilla/show_bug.cgi?id=27215 +config AS_HAS_NON_CONST_ULEB128 def_bool $(as-instr,.uleb128 .Lexpr_end4 - .Lexpr_start3\n.Lexpr_start3:\n.Lexpr_end4:) choice @@ -258,7 +259,7 @@ 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 && AS_HAS_NON_CONST_LEB128) + depends on !CC_IS_CLANG || AS_IS_LLVM || CLANG_VERSION < 140000 || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_ULEB128) help The implicit default version of DWARF debug info produced by a toolchain changes over time. @@ -283,7 +284,7 @@ config DEBUG_INFO_DWARF5 bool "Generate DWARF Version 5 debuginfo" select DEBUG_INFO depends on !ARCH_HAS_BROKEN_DWARF5 - depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_LEB128) + depends on !CC_IS_CLANG || AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502 && AS_HAS_NON_CONST_ULEB128) 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 -- cgit v1.2.3