[llvm] [llvm-objcopy] Fix file offsets when PT_INTERP/PT_LOAD offsets are equal (PR #80562)
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Sat Feb 3 12:16:09 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-binary-utilities
Author: Fangrui Song (MaskRay)
<details>
<summary>Changes</summary>
(#<!-- -->79887) When the offset of a PT_INTERP segment equals the offset of a
PT_LOAD segment, we consider that the parent of the PT_LOAD segment is
the PT_INTERP segment. In `layoutSegments`, we place both segments to be
after the current `Offset`, ignoring the PT_LOAD alignment.
This scenario is possible with fixed section addresses, but doesn't
happen with default linker layouts (.interp precedes other sections and
is part of a PT_LOAD segment containing the ELF header and program
headers).
```
% cat a.s
.globl _start; _start: ret
.rodata; .byte 0
.tdata; .balign 4096; .byte 0
% clang -fuse-ld=lld a.s -o a -nostdlib -no-pie -z separate-loadable-segments -Wl,-Ttext=0x201000,--section-start=.interp=0x202000,--section-start=.rodata=0x202020,-z,nognustack
% llvm-objcopy a a2
% llvm-readelf -l a2 # incorrect offset(PT_LOAD)
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
PHDR 0x000040 0x0000000000200040 0x0000000000200040 0x0001c0 0x0001c0 R 0x8
INTERP 0x001001 0x0000000000202000 0x0000000000202000 0x00001c 0x00001c R 0x1
[Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
LOAD 0x000000 0x0000000000200000 0x0000000000200000 0x000200 0x000200 R 0x1000
LOAD 0x001000 0x0000000000201000 0x0000000000201000 0x000001 0x000001 R E 0x1000
//// incorrect offset
LOAD 0x001001 0x0000000000202000 0x0000000000202000 0x000021 0x000021 R 0x1000
LOAD 0x002000 0x0000000000203000 0x0000000000203000 0x000001 0x001000 RW 0x1000
TLS 0x002000 0x0000000000203000 0x0000000000203000 0x000001 0x000001 R 0x1000
GNU_RELRO 0x002000 0x0000000000203000 0x0000000000203000 0x000001 0x001000 R 0x1000
```
The same issue occurs for PT_TLS/PT_GNU_RELRO if we PT_TLS's alignment
is smaller and we place the PT_LOAD after PT_TLS/PT_GNU_RELRO segments
(not linker default, but possible with a `PHDRS` linker script command).
Fix #<!-- -->79887: set the parent of the PT_INTERP segment to the PT_LOAD
segment when their addresses are equal.
---
Full diff: https://github.com/llvm/llvm-project/pull/80562.diff
2 Files Affected:
- (modified) llvm/lib/ObjCopy/ELF/ELFObject.cpp (+7)
- (added) llvm/test/tools/llvm-objcopy/ELF/non-load-at-load-start.test (+138)
``````````diff
diff --git a/llvm/lib/ObjCopy/ELF/ELFObject.cpp b/llvm/lib/ObjCopy/ELF/ELFObject.cpp
index c8b66d6fcb5eb..edf0b53faf96d 100644
--- a/llvm/lib/ObjCopy/ELF/ELFObject.cpp
+++ b/llvm/lib/ObjCopy/ELF/ELFObject.cpp
@@ -1234,6 +1234,13 @@ static bool compareSegmentsByOffset(const Segment *A, const Segment *B) {
return true;
if (A->OriginalOffset > B->OriginalOffset)
return false;
+ // If one is PT_LOAD and the other isn't (e.g. PT_INTERP, PT_GNU_RELRO,
+ // PT_TLS), order the PT_LOAD first to ensure ParentSegment relationship will
+ // be correct.
+ bool AIsLOAD = A->Type == PT_LOAD;
+ bool BIsLOAD = B->Type == PT_LOAD;
+ if (AIsLOAD != BIsLOAD)
+ return AIsLOAD;
return A->Index < B->Index;
}
diff --git a/llvm/test/tools/llvm-objcopy/ELF/non-load-at-load-start.test b/llvm/test/tools/llvm-objcopy/ELF/non-load-at-load-start.test
new file mode 100644
index 0000000000000..7551b6473379f
--- /dev/null
+++ b/llvm/test/tools/llvm-objcopy/ELF/non-load-at-load-start.test
@@ -0,0 +1,138 @@
+## When the offset of a non-PT_LOAD segment (e.g. PT_INTERP) equals the offset
+## of a PT_LOAD segment, set the parent of the PT_INTERP segment to the PT_LOAD
+## segment, ensuring that the offset is correctly aligned.
+
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-objcopy %t %t2
+# RUN: llvm-readelf -Sl %t2 | FileCheck %s
+
+# CHECK: [Nr] Name Type Address Off Size ES Flg Lk Inf Al
+# CHECK-NEXT: [ 0] NULL 0000000000000000 000000 000000 00 0 0 0
+# CHECK-NEXT: [ 1] .text PROGBITS 0000000000201000 001000 000001 00 AX 0 0 4
+# CHECK-NEXT: [ 2] .interp PROGBITS 0000000000202000 002000 00001c 00 A 0 0 1
+# CHECK-NEXT: [ 3] .rodata PROGBITS 0000000000202020 002020 000001 00 A 0 0 1
+# CHECK-NEXT: [ 4] .tdata PROGBITS 0000000000203000 003000 000001 00 WAT 0 0 4096
+# CHECK-NEXT: [ 5] .relro_padding NOBITS 0000000000203001 003001 000fff 00 WA 0 0 1
+# CHECK-NEXT: [ 6] .symtab SYMTAB 0000000000000000 003008 000030 18 7 1 8
+# CHECK-NEXT: [ 7] .strtab STRTAB 0000000000000000 003038 000008 00 0 0 1
+# CHECK-NEXT: [ 8] .shstrtab STRTAB 0000000000000000 003040 000047 00 0 0 1
+
+# CHECK: Program Headers:
+# CHECK-NEXT: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
+# CHECK-NEXT: PHDR 0x000040 0x0000000000200040 0x0000000000200040 0x0001c0 0x0001c0 R 0x8
+# CHECK-NEXT: INTERP 0x002000 0x0000000000202000 0x0000000000202000 0x00001c 0x00001c R 0x1
+# CHECK-NEXT: [Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
+# CHECK-NEXT: LOAD 0x000000 0x0000000000200000 0x0000000000200000 0x000200 0x000200 R 0x1000
+# CHECK-NEXT: LOAD 0x001000 0x0000000000201000 0x0000000000201000 0x000001 0x000001 R E 0x1000
+# CHECK-NEXT: LOAD 0x002000 0x0000000000202000 0x0000000000202000 0x000021 0x000021 R 0x1000
+# CHECK-NEXT: TLS 0x003000 0x0000000000203000 0x0000000000203000 0x000001 0x001000 R 0x1000
+# CHECK-NEXT: GNU_RELRO 0x003000 0x0000000000203000 0x0000000000203000 0x000001 0x001000 R 0x1000
+# CHECK-NEXT: LOAD 0x003000 0x0000000000203000 0x0000000000203000 0x000001 0x001000 RW 0x1000
+
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_EXEC
+ Machine: EM_X86_64
+ Entry: 0x201000
+ProgramHeaders:
+ - Type: PT_PHDR
+ Flags: [ PF_R ]
+ VAddr: 0x200040
+ Align: 0x8
+ Offset: 0x40
+ FileSize: 0x1c0
+ MemSize: 0x1c0
+ - Type: PT_INTERP
+ Flags: [ PF_R ]
+ FirstSec: .interp
+ LastSec: .interp
+ ## The address equals the address of its containing PT_LOAD.
+ VAddr: 0x202000
+ Offset: 0x2000
+ - Type: PT_LOAD
+ Flags: [ PF_R ]
+ VAddr: 0x200000
+ Align: 0x1000
+ Offset: 0x0
+ FileSize: 0x200
+ MemSize: 0x200
+ - Type: PT_LOAD
+ Flags: [ PF_X, PF_R ]
+ FirstSec: .text
+ LastSec: .text
+ VAddr: 0x201000
+ Align: 0x1000
+ Offset: 0x1000
+ - Type: PT_LOAD
+ Flags: [ PF_R ]
+ FirstSec: .interp
+ LastSec: .rodata
+ VAddr: 0x202000
+ Align: 0x1000
+ Offset: 0x2000
+ ## Intentionally place PT_TLS/PT_GNU_RELRO before PT_LOAD to test that we
+ ## correctly set parent segments.
+ - Type: PT_TLS
+ Flags: [ PF_R ]
+ FirstSec: .tdata
+ LastSec: .relro_padding
+ VAddr: 0x203000
+ Align: 0x1000
+ Offset: 0x3000
+ - Type: PT_GNU_RELRO
+ Flags: [ PF_R ]
+ FirstSec: .tdata
+ LastSec: .relro_padding
+ VAddr: 0x203000
+ Align: 0x1000
+ Offset: 0x3000
+ - Type: PT_LOAD
+ Flags: [ PF_W, PF_R ]
+ FirstSec: .tdata
+ LastSec: .relro_padding
+ VAddr: 0x203000
+ Align: 0x1000
+ Offset: 0x3000
+Sections:
+ - Name: .text
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
+ Address: 0x201000
+ AddressAlign: 0x4
+ Offset: 0x1000
+ Content: C3
+ - Name: .interp
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0x202000
+ AddressAlign: 0x1
+ Offset: 0x2000
+ Content: 2F6C696236342F6C642D6C696E75782D7838362D36342E736F2E3200
+ - Name: .rodata
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0x202020
+ AddressAlign: 0x1
+ Offset: 0x2020
+ Content: '00'
+ - Name: .tdata
+ Type: SHT_PROGBITS
+ Flags: [ SHF_WRITE, SHF_ALLOC, SHF_TLS ]
+ Address: 0x203000
+ AddressAlign: 0x1000
+ Offset: 0x3000
+ Content: '00'
+ - Name: .relro_padding
+ Type: SHT_NOBITS
+ Flags: [ SHF_WRITE, SHF_ALLOC ]
+ Address: 0x203001
+ AddressAlign: 0x1
+ Size: 0xFFF
+Symbols:
+ - Name: _start
+ Section: .text
+ Binding: STB_GLOBAL
+ Value: 0x201000
+...
``````````
</details>
https://github.com/llvm/llvm-project/pull/80562
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