26ddf4eee2
`clang -g -gpubnames -fdebug-types-section` now emits .debug_names
section with references to local type unit entries defined in COMDAT
.debug_info sections.
```
.section .debug_info,"G",@progbits,5657452045627120676,comdat
.Ltu_begin0:
...
.section .debug_names,"",@progbits
...
// DWARF32
.long .Ltu_begin0 # Type unit 0
// DWARF64
// .long .Ltu_begin0 # Type unit 0
```
When `.Ltu_begin0` is relative to a non-prevailing .debug_info section,
the relocation resolves to 0, which is a valid offset within the
.debug_info section.
```
cat > a.cc <<e
struct A { int x; };
inline A foo() { return {1}; }
int main() { foo(); }
e
cat > b.cc <<e
struct A { int x; };
inline A foo() { return {1}; }
void use() { foo(); }
e
clang++ -g -gpubnames -fdebug-types-section -fuse-ld=lld a.cc b.cc -o old
```
```
% llvm-dwarfdump old
...
Local Type Unit offsets [
LocalTU[0]: 0x00000000
]
...
Local Type Unit offsets [
LocalTU[0]: 0x00000000 // indistinguishable from a valid offset within .debug_info
]
```
https://dwarfstd.org/issues/231013.1.html proposes that we use a
tombstone value instead to inform consumers. This patch implements the
idea. The second LocalTU entry will now use 0xffffffff.
https://reviews.llvm.org/D84825 has a TODO that we should switch the
tombstone value for most `.debug_*` sections to UINT64_MAX. We have
postponed the change for more than three years for consumers to migrate.
At some point we shall make the change, so that .debug_names is no long
different from other debug section that is not .debug_loc/.debug_ranges.
Co-authored-by: Alexander Yermolovich <ayermolo@meta.com>
113 lines
4.1 KiB
ArmAsm
113 lines
4.1 KiB
ArmAsm
# REQUIRES: aarch64, x86
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## Test we resolve symbolic relocations in .debug_* sections to a tombstone
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## value if the referenced symbol is discarded (--gc-sections, non-prevailing
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## section group, SHF_EXCLUDE, /DISCARD/, etc).
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# RUN: echo '.globl _start; _start: call group' | llvm-mc -filetype=obj -triple=x86_64 - -o %t.o
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# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t1.o
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# RUN: ld.lld --emit-relocs --gc-sections %t.o %t1.o %t1.o -o %t
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# RUN: llvm-objdump -s %t | FileCheck %s
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# RUN: llvm-readobj -r %t | FileCheck %s --check-prefix=REL
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# RUN: echo '.globl _start; _start: bl group' | llvm-mc -filetype=obj -triple=aarch64 - -o %t.a64.o
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# RUN: llvm-mc -filetype=obj -triple=aarch64 %s -o %t1.a64.o
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# RUN: ld.lld --emit-relocs --gc-sections %t.a64.o %t1.a64.o %t1.a64.o -o %t.a64
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# RUN: llvm-objdump -s %t.a64 | FileCheck %s
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# CHECK: Contents of section .debug_loc:
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# CHECK-NEXT: 0000 01000000 00000000 01000000 00000000
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# CHECK: Contents of section .debug_ranges:
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# CHECK-NEXT: 0000 01000000 00000000 01000000 00000000
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# CHECK: Contents of section .debug_addr:
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# CHECK-NEXT: 0000 {{.*}}00 00000000 {{.*}}00 00000000
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# CHECK-NEXT: 0010 00000000 00000000 {{.*}}00 00000000
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# CHECK: Contents of section .debug_names:
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# CHECK-NEXT: 0000 00000000 00000000 00000000 ffffffff .
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# CHECK-NEXT: 0010 ffffffff ffffffff .
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# CHECK: Contents of section .debug_foo:
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# CHECK-NEXT: 0000 00000000 00000000 00000000 00000000
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# CHECK-NEXT: 0010 00000000 00000000 00000000 00000000
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# REL: Relocations [
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# REL-NEXT: .rela.text {
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# REL-NEXT: 0x201121 R_X86_64_PLT32 group 0xFFFFFFFFFFFFFFFC
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# REL-NEXT: }
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# REL-NEXT: .rela.debug_loc {
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# REL-NEXT: 0x0 R_X86_64_NONE - 0x8
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# REL-NEXT: 0x8 R_X86_64_NONE - 0x8
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# REL-NEXT: }
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# REL-NEXT: .rela.debug_ranges {
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# REL-NEXT: 0x0 R_X86_64_NONE - 0x10
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# REL-NEXT: 0x8 R_X86_64_NONE - 0x10
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# REL-NEXT: }
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# REL-NEXT: .rela.debug_addr {
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# REL-NEXT: 0x0 R_X86_64_64 .text 0x1D
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# REL-NEXT: 0x8 R_X86_64_64 group 0x20
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# REL-NEXT: 0x10 R_X86_64_NONE - 0x18
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# REL-NEXT: 0x18 R_X86_64_64 group 0x20
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# REL-NEXT: }
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# REL-NEXT: .rela.debug_names {
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# REL-NEXT: 0x0 R_X86_64_32 .debug_info 0x0
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# REL-NEXT: 0x4 R_X86_64_64 .debug_info 0x0
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# REL-NEXT: 0xC R_X86_64_NONE - 0x0
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# REL-NEXT: 0x10 R_X86_64_NONE - 0x0
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# REL-NEXT: }
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# REL-NEXT: .rela.debug_foo {
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# REL-NEXT: 0x0 R_X86_64_NONE - 0x8
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# REL-NEXT: 0x8 R_X86_64_NONE - 0x8
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# REL-NEXT: 0x10 R_X86_64_NONE - 0x8
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# REL-NEXT: 0x18 R_X86_64_NONE - 0x8
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# REL-NEXT: }
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# REL-NEXT: ]
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## -z dead-reloc-in-nonalloc= can override the tombstone value.
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# RUN: ld.lld --gc-sections -z dead-reloc-in-nonalloc=.debug_loc=42 %t.o %t1.o %t1.o -o %t42
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# RUN: llvm-objdump -s %t42 | FileCheck %s --check-prefix=OVERRIDE
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# OVERRIDE: Contents of section .debug_loc:
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# OVERRIDE-NEXT: 0000 2a000000 00000000 2a000000 00000000
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.section .text.1,"ax"
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.byte 0
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.section .text.2,"axe"
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.byte 0
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.section .text.3,"axG",@progbits,group,comdat
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.globl group
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group:
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.byte 0
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## Resolved to UINT64_C(1), with the addend ignored.
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## UINT64_C(-1) is a reserved value (base address selection entry) which can't be used.
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.section .debug_loc
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.quad .text.1+8
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.section .debug_ranges
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.quad .text.2+16
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.section .debug_addr
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## .text.3 is a local symbol. The symbol defined in a non-prevailing group is
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## discarded. Resolved to UINT64_C(0).
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.quad .text.3+24
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## group is a non-local symbol. The relocation from the second %t1.o gets
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## resolved to the prevailing copy.
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.quad group+32
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.section .debug_info,"G",@progbits,5657452045627120676,comdat
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.Ltu_begin0:
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.section .debug_names
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## .debug_names may reference a local type unit defined in a COMDAT .debug_info
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## section (-g -gpubnames -fdebug-types-section). If the referenced section is
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## non-prevailing, resolve to UINT32_MAX.
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.long .Ltu_begin0
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## ... or UINT64_MAX for DWARF64.
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.quad .Ltu_begin0
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.section .debug_foo
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.quad .text.1+8
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## We only deal with DW_FORM_addr. Don't special case short-range absolute
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## relocations. Treat them like regular absolute relocations referencing
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## discarded symbols, which are resolved to the addend.
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.long .text.1+8
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.long 0
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