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
Link: https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a
Link: https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Fangrui Song <maskray@google.com>
Link: https://lore.kernel.org/r/20231205-riscv-restrict-dwarf5-llvm-v2-2-aedf00a382ac@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 72be1d8122a3cc37707317cf4b943f0e347152a7..81b473cb47b05ded6d389f251aeee06c5a06060b 100644 (file)
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -186,6 +186,15 @@ config RISCV_USE_LINKER_RELAXATION
        # https://github.com/llvm/llvm-project/commit/6611d58f5bbcbec77262d392e2923e1d680f6985
        depends on !LD_IS_LLD || LLD_VERSION >= 150000
 
+# https://github.com/llvm/llvm-project/commit/bbc0f99f3bc96f1db16f649fc21dd18e5b0918f6
+config ARCH_HAS_BROKEN_DWARF5
+       def_bool y
+       depends on RISCV_USE_LINKER_RELAXATION
+       # https://github.com/llvm/llvm-project/commit/1df5ea29b43690b6622db2cad7b745607ca4de6a
+       depends on AS_IS_LLVM && AS_VERSION < 180000
+       # https://github.com/llvm/llvm-project/commit/7ffabb61a5569444b5ac9322e22e5471cc5e4a77
+       depends on LD_IS_LLD && LLD_VERSION < 180000
+
 config ARCH_MMAP_RND_BITS_MIN
        default 18 if 64BIT
        default 8

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index cc7d53d9dc0191c544b0e2a71d0a6500b854924c..a0ebce05a368fd89470449624511a5b19418dfff 100644 (file)
--- 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