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[SHT_LLVM_FUNC_MAP][ObjectYaml]Introduce function address map section and emit dynamic instruction count(ObjectYaml part) #124332

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[SHT_LLVM_FUNC_MAP][ObjectYaml]Introduce function address map section and emit dynamic instruction count(ObjectYaml part) #124332

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2e0f4ff
[𝘀𝗽𝗿] initial version
wlei-llvm Jan 24, 2025
d2b1895
addressing comments
wlei-llvm Jan 27, 2025
5841112
addressing comments
wlei-llvm Jan 27, 2025
cc11306
fix doc format
wlei-llvm Jan 28, 2025
e8a1dce
address feedback
wlei-llvm Feb 12, 2025
d2d627e
fix doc format
wlei-llvm Feb 12, 2025
970042e
Use fixed size instead of ULEBs
wlei-llvm Feb 12, 2025
3703e53
set entry size
wlei-llvm Feb 15, 2025
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10 changes: 7 additions & 3 deletions llvm/lib/ObjectYAML/ELFEmitter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1550,18 +1550,22 @@ void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
return;

for (const auto &[Idx, E] : llvm::enumerate(*Section.Entries)) {
unsigned Size = 0;
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@jh7370 jh7370 Feb 21, 2025

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The size setting code in this loop could be dramatically simplified for now, now that we're using fixed size entries. Outside the loop, you could just do something like:

SHeader.sh_entsize = 9 + sizeof(uintX_t);
SHeader.sh_size = Section.Entries->size() * SHeader.sh_entsize;

if (Section.Type == llvm::ELF::SHT_LLVM_FUNC_MAP) {
if (E.Version > 1)
WithColor::warning() << "unsupported SHT_LLVM_FUNC_MAP version: "
<< static_cast<int>(E.Version)
<< "; encoding using the most recent version";
CBA.write(E.Version);
SHeader.sh_size += 1;
Size += 1;
}
CBA.write<uintX_t>(E.Address, ELFT::Endianness);
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@jh7370 jh7370 Feb 21, 2025

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Correct me if I'm wrong, but shouldn't this be using the Elf_Addr type, since it's representing an address? They might amount to the same thing, but it conveys the meaning better. (NB: I haven't tested it, so this might not work as desired)

Suggested change
CBA.write<uintX_t>(E.Address, ELFT::Endianness);
CBA.write<ELFT::Elf_Addr>(E.Address, ELFT::Endianness);

SHeader.sh_size += sizeof(uintX_t);
Size += sizeof(uintX_t);
CBA.write<uint64_t>(E.DynamicInstCount, ELFT::Endianness);
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@jh7370 jh7370 Feb 21, 2025

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I wonder if the DynamicInstCount should be architecture-dependent type, so that on 32-bit architectures, it only takes up 4 bytes? There's probably an argument actually that it should always just be 4 bytes, since you'd be hard pressed to need more than what 4 bytes can represent in instruction counts.

SHeader.sh_size += 8;
Size += 8;

SHeader.sh_size += Size;
SHeader.sh_entsize = Size;
}
}

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4 changes: 4 additions & 0 deletions llvm/test/tools/obj2yaml/ELF/func-map.yaml
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Expand Up @@ -13,6 +13,7 @@
# VALID-NEXT: Sections:
# VALID-NEXT: - Name: .llvm_func_map
# VALID-NEXT: Type: SHT_LLVM_FUNC_MAP
# VALID-NEXT: EntSize: 0x11
# VALID-NEXT: Entries:
# VALID-NEXT: - Version: 1
## The 'Address' field is omitted when it's zero.
Expand Down Expand Up @@ -82,12 +83,14 @@ Sections:
# MULTI-NEXT: Sections:
# MULTI-NEXT: - Name: .llvm_func_map
# MULTI-NEXT: Type: SHT_LLVM_FUNC_MAP
# MULTI-NEXT: EntSize: 0x11
# MULTI-NEXT: Entries:
# MULTI-NEXT: - Version: 1
# MULTI-NEXT: Address: 0x2
# MULTI-NEXT: DynInstCnt: 3
# MULTI-NEXT: - Name: '.llvm_func_map (1)'
# MULTI-NEXT: Type: SHT_LLVM_FUNC_MAP
# MULTI-NEXT: EntSize: 0x11
# MULTI-NEXT: Entries:
# MULTI-NEXT: - Version: 1
# MULTI-NEXT: Address: 0xA
Expand Down Expand Up @@ -127,4 +130,5 @@ Sections:
# INVALID-NEXT: Sections:
# INVALID-NEXT: - Name: .llvm_func_map
# INVALID-NEXT: Type: SHT_LLVM_FUNC_MAP
# INVALID-NEXT: EntSize: 0x11
# TRUNCATED-NEXT: Content: '{{([[:xdigit:]]{16})}}'{{$}}
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@jh7370 jh7370 Feb 21, 2025

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I'd be tempted to explicitly check the expected 8 bytes here, to show that it's not producing garbage here.