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DWARF v5 .debug_loclists/.debug_rnglists's
DW_LLE_offset_pair/DW_RLE_offset_pair entry kinds utilitize `.uleb128 A-B`
directives where A and B reference local labels in code sections.
When A and B are separated by a RISC-V linker-relaxable instruction,
A-B is incorrectly folded without a relocation, causing incorrect debug
information.
void ext(void);
int foo(int x) {ext(); return 0;}
// DW_AT_location [DW_FORM_loclistx] of a DW_TAG_formal_parameter references
a DW_LLE_offset_pair that can be incorrect after linker relaxation.
int ext(void);
void foo() { {
int ret = ext();
if (__builtin_expect(ret, 0))
ext();
} }
// DW_AT_ranges [DW_FORM_rnglistx] of a DW_TAG_lexical_block references a
DW_RLE_offset_pair that can be incorrect after linker relaxation.
D157657 <https://reviews.llvm.org/D157657> will implement
R_RISCV_SET_ULEB128/R_RISCV_SUB_ULEB128
relocations, fixing the issue, but the relocation is only supported by
bleeding-edge binutils 2.41 and not by lld/ELF yet.
The goal is to make the emitted DWARF correct after linking.
Many users don't care about the default DWARF version, but a linker
error will be unacceptable. Let's just downgrade the default DWARF
version, before binutils>=2.41 is more widely available.
An alternative compatibility option is to add a toggle to DwarfDebug.cpp,
but that doesn't seem like a good idea.
This patch is planned for the main and release/17.x branches.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D157663
Files:
clang/lib/Driver/ToolChains/Linux.cpp
clang/test/Driver/clang-g-opts.c
Index: clang/test/Driver/clang-g-opts.c
===================================================================
--- clang/test/Driver/clang-g-opts.c
+++ clang/test/Driver/clang-g-opts.c
@@ -37,3 +37,7 @@
// CHECK-WITH-G-STANDALONE: "-debug-info-kind=standalone"
// CHECK-WITH-G-STANDALONE: "-dwarf-version=2"
+
+// RUN: %clang -### -S %s -g --target=riscv64-linux-gnu 2>&1 \
+// RUN: | FileCheck --check-prefix=VERSION4 %s
+// VERSION4: "-dwarf-version=4"
Index: clang/lib/Driver/ToolChains/Linux.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Linux.cpp
+++ clang/lib/Driver/ToolChains/Linux.cpp
@@ -343,7 +343,7 @@
}
unsigned Linux::GetDefaultDwarfVersion() const {
- if (getTriple().isAndroid())
+ if (getTriple().isAndroid() || getTriple().isRISCV())
return 4;
return ToolChain::GetDefaultDwarfVersion();
}
Index: clang/test/Driver/clang-g-opts.c
===================================================================
--- clang/test/Driver/clang-g-opts.c
+++ clang/test/Driver/clang-g-opts.c
@@ -37,3 +37,7 @@
// CHECK-WITH-G-STANDALONE: "-debug-info-kind=standalone"
// CHECK-WITH-G-STANDALONE: "-dwarf-version=2"
+
+// RUN: %clang -### -S %s -g --target=riscv64-linux-gnu 2>&1 \
+// RUN: | FileCheck --check-prefix=VERSION4 %s
+// VERSION4: "-dwarf-version=4"
Index: clang/lib/Driver/ToolChains/Linux.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Linux.cpp
+++ clang/lib/Driver/ToolChains/Linux.cpp
@@ -343,7 +343,7 @@
}
unsigned Linux::GetDefaultDwarfVersion() const {
- if (getTriple().isAndroid())
+ if (getTriple().isAndroid() || getTriple().isRISCV())
return 4;
return ToolChain::GetDefaultDwarfVersion();
}
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