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[SHT_LLVM_BB_ADDR_MAP] Support decompressing the SHT_LLVM_BB_ADDR_MAP section. (#142825)
Compression of SHT_LLVM_BB_ADDR_MAP with zstd can give 3X compression ratio, which is especially beneficial with PGO_analysis_map. To read the data back, we must decompress it. Though we can use llvm-objcopy to do this, it's much better to do this decompression internally in the library API.
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‎llvm/lib/Object/ELF.cpp

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@@ -9,6 +9,7 @@
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#include "llvm/Object/ELF.h"
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#include "llvm/ADT/StringExtras.h"
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#include "llvm/BinaryFormat/ELF.h"
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#include "llvm/Object/Decompressor.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/DataExtractor.h"
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@@ -782,6 +783,27 @@ decodeBBAddrMapImpl(const ELFFile<ELFT> &EF,
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if (!ContentsOrErr)
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return ContentsOrErr.takeError();
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ArrayRef<uint8_t> Content = *ContentsOrErr;
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// Decompress the section if needed.
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std::unique_ptr<uint8_t[]> DecompressedContent;
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if (Sec.sh_flags & llvm::ELF::SHF_COMPRESSED) {
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Expected<StringRef> SectionNameOrErr = EF.getSectionName(Sec);
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if (!SectionNameOrErr)
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return SectionNameOrErr.takeError();
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auto DecompressorOrErr =
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Decompressor::create(*SectionNameOrErr, toStringRef(*ContentsOrErr),
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EF.isLE(), ELFT::Is64Bits);
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if (!DecompressorOrErr)
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return DecompressorOrErr.takeError();
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size_t DecompressedSize = DecompressorOrErr->getDecompressedSize();
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DecompressedContent = std::make_unique<uint8_t[]>(DecompressedSize);
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MutableArrayRef<uint8_t> DecompressedContentRef(DecompressedContent.get(),
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DecompressedSize);
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if (Error Err = DecompressorOrErr->decompress(DecompressedContentRef))
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return std::move(Err);
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Content = DecompressedContentRef;
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}
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DataExtractor Data(Content, EF.isLE(), ELFT::Is64Bits ? 8 : 4);
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std::vector<BBAddrMap> FunctionEntries;
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‎llvm/test/tools/llvm-readobj/ELF/bb-addr-map-compressed-zstd.test

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# REQUIRES: zstd
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## This test checks that we can read compressed SHT_LLVM_BB_ADDR_MAP sections.
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## Check 64-bit:
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# RUN: yaml2obj --docnum=1 %s -DBITS=64 -DADDR=0x999999999 -o %t1.x64.o
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# RUN: llvm-objcopy %t1.x64.o --compress-sections .llvm_bb_addr_map=zstd %t1.x64.compressed.o
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# RUN: llvm-readobj %t1.x64.compressed.o --bb-addr-map 2>&1 | FileCheck %s -DADDR=0x999999999 -DFILE=%t1.x64.compressed.o --check-prefix=CHECK
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## Check 32-bit:
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# RUN: yaml2obj --docnum=1 %s -DBITS=32 -o %t1.x32.o
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# RUN: llvm-objcopy %t1.x32.o --compress-sections .llvm_bb_addr_map=zstd %t1.x32.compressed.o
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# RUN: llvm-readobj %t1.x32.compressed.o --bb-addr-map 2>&1 | FileCheck %s -DADDR=0x11111 -DFILE=%t1.x32.compressed.o --check-prefix=CHECK
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# CHECK: BBAddrMap [
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# CHECK-NEXT: Function {
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# CHECK-NEXT: At: [[ADDR]]
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# CHECK-NEXT: warning: '[[FILE]]': could not identify function symbol for address ([[ADDR]]) in SHT_LLVM_BB_ADDR_MAP section with index 3
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# CHECK-NEXT: Name: <?>
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# CHECK-NEXT: BB Ranges [
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# CHECK-NEXT: {
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# CHECK-NEXT: Base Address: [[ADDR]]
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# CHECK-NEXT: BB Entries [
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# CHECK-NEXT: {
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# CHECK-NEXT: ID: 0
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# CHECK-NEXT: Offset: 0x0
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# CHECK-NEXT: Size: 0x1
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# CHECK-NEXT: HasReturn: No
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# CHECK-NEXT: HasTailCall: Yes
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# CHECK-NEXT: IsEHPad: No
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# CHECK-NEXT: CanFallThrough: No
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# CHECK-NEXT: HasIndirectBranch: No
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# CHECK-NEXT: }
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# CHECK-NEXT: ]
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# CHECK-NEXT: }
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# CHECK-NEXT: {
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# CHECK-NEXT: Base Address: 0x44444
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# CHECK-NEXT: BB Entries [
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# CHECK-NEXT: {
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# CHECK-NEXT: ID: 2
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# CHECK-NEXT: Offset: 0x3
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# CHECK-NEXT: Size: 0x4
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# CHECK-NEXT: HasReturn: Yes
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# CHECK-NEXT: HasTailCall: No
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# CHECK-NEXT: IsEHPad: Yes
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# CHECK-NEXT: CanFallThrough: No
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# CHECK-NEXT: HasIndirectBranch: Yes
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# CHECK-NEXT: }
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# CHECK-NEXT: ]
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# CHECK-NEXT: }
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# CHECK-NEXT: ]
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# CHECK-NEXT: }
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# CHECK-NEXT: Function {
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# CHECK-NEXT: At: 0x22222
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# CHECK-NEXT: Name: foo
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# CHECK-NEXT: BB Ranges [
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# CHECK-NEXT: {
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# CHECK-NEXT: Base Address: 0x22222
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# CHECK-NEXT: BB Entries [
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# CHECK-NEXT: {
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# CHECK-NEXT: ID: 4
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# CHECK-NEXT: Offset: 0x6
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# CHECK-NEXT: Size: 0x7
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# CHECK-NEXT: HasReturn: No
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# CHECK-NEXT: HasTailCall: No
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# CHECK-NEXT: IsEHPad: No
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# CHECK-NEXT: CanFallThrough: Yes
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# CHECK-NEXT: HasIndirectBranch: No
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# CHECK-NEXT: }
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# CHECK-NEXT: ]
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# CHECK-NEXT: }
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# CHECK-NEXT: ]
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# CHECK-NEXT: }
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# CHECK-NEXT: ]
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--- !ELF
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FileHeader:
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Class: ELFCLASS[[BITS]]
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Data: ELFDATA2LSB
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Type: ET_EXEC
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Sections:
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- Name: .text
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Type: SHT_PROGBITS
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Flags: [SHF_ALLOC]
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- Name: .text.bar
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Type: SHT_PROGBITS
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Flags: [SHF_ALLOC]
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- Name: .llvm_bb_addr_map
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Type: SHT_LLVM_BB_ADDR_MAP
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ShSize: [[SIZE=<none>]]
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Link: .text
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Entries:
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- Version: 2
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Feature: 0x8
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BBRanges:
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- BaseAddress: [[ADDR=0x11111]]
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BBEntries:
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- ID: 0
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AddressOffset: 0x0
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Size: 0x1
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Metadata: [[METADATA=0x2]]
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- BaseAddress: 0x44444
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BBEntries:
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- ID: 2
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AddressOffset: 0x3
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Size: 0x4
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Metadata: 0x15
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- Version: 2
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BBRanges:
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- BaseAddress: 0x22222
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BBEntries:
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- ID: 4
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AddressOffset: 0x6
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Size: 0x7
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Metadata: 0x8
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- Name: dummy_section
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Type: SHT_PROGBITS
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Size: 16
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- Name: '.llvm_bb_addr_map (1)'
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Type: SHT_LLVM_BB_ADDR_MAP
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Link: .text.bar
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Entries:
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- Version: 2
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BBRanges:
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- BaseAddress: 0x33333
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BBEntries:
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- ID: 6
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AddressOffset: 0x9
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Size: 0xa
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Metadata: 0x1b
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- ID: 7
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AddressOffset: 0xc
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Size: 0xd
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Metadata: 0xe
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Symbols:
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- Name: foo
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Section: .text
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Type: STT_FUNC
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Value: 0x22222
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- Name: bar
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Section: .text.bar
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Type: STT_FUNC
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Value: 0x33333

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