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 <maskray@google.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20231205-riscv-restrict-dwarf5-llvm-v2-3-aedf00a382ac@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index a0ebce05a368fd89470449624511a5b19418dfff..76c2cc697573102bcbe7dcecfcccc53439bfb5c7 100644 (file)
--- 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