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[llvm-objdump] Print out xcoff load section of xcoff object file with option private-headers #121226

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Jan 20, 2025
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[llvm-objdump] Print out xcoff load section of xcoff object file with option private-headers #121226

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[llvm-objdump] Print out xcoff file header for xcoff object file with…
diggerlin Dec 27, 2024
dce5109
minor change
diggerlin Dec 27, 2024
2ecfb53
add warnning test scenario
diggerlin Jan 14, 2025
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83 changes: 83 additions & 0 deletions llvm/test/tools/llvm-objdump/XCOFF/private-headers-option.test
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Original file line number Diff line number Diff line change
@@ -0,0 +1,83 @@
## Test the --private-headers option for the loader section of XCOFF object files.

# RUN: yaml2obj --docnum=1 %s -o %t_xcoff32.o
# RUN: yaml2obj --docnum=2 %s -o %t_xcoff64.o
# RUN: llvm-objdump --private-headers %t_xcoff32.o |\
# RUN: FileCheck %s --check-prefixes=CHECK32 --match-full-lines
# RUN: llvm-objdump --private-headers %t_xcoff64.o |\
# RUN: FileCheck %s --check-prefixes=CHECK64 --match-full-lines

--- !XCOFF
FileHeader:
MagicNumber: 0x1DF
Sections:
- Name: .loader
Flags: [ STYP_LOADER ]
SectionData: "0000000100000003000000050000016D00000001000000A40000001800000211"
## ^------- -Version=1
## ^------- -NumberOfSymbolEntries=3
## ^------- -NumberOfRelocationEntries=5
## ^------- -LengthOfImportFileIDStringTable=365
## ^------- -NumberOfImportFileIDs=1
## ^------- -OffsetToImportFileIDs=0xA4
## ^------- -LengthOfStringTable=24
## ^------- -OffsetToStringTable=0x211


--- !XCOFF
FileHeader:
MagicNumber: 0x1F7
Sections:
- Name: .loader
Flags: [ STYP_LOADER ]
SectionData: "0000000200000003000000050000016D000000010000002300000000000000D0000000000000023D00000000000000380000000000000080"
## ^------- -Version=2
## ^------- -NumberOfSymbolEntries=3
## ^------- -NumberOfRelocationEntries=5
## ^------- -LengthOfImportFileIDStringTable=365
## ^------- -NumberOfImportFileIDs=1
## ^------- --LengthOfStringTable=0x23
## ^--------------- -OffsetToImportFileIDs=0xD0
## ^--------------- -OffsetToStringTable=0x23D
## ^-------------- -OffsetToSymbolTable=0x38
## ^--------------- -OffsetToRelocationEntries=0x80

# CHECK32: ---File Header:
# CHECK32-NEXT: Magic: 0x1df
# CHECK32-NEXT: NumberOfSections: 1
# CHECK32-NEXT: Timestamp: None (0)
# CHECK32-NEXT: SymbolTableOffset: 0x0
# CHECK32-NEXT: SymbolTableEntries: 0
# CHECK32-NEXT: OptionalHeaderSize: 0x0
# CHECK32-NEXT: Flags: 0x0

# CHECK32: ---Loader Section Header:
# CHECK32-NEXT: Version: 1
# CHECK32-NEXT: NumberOfSymbolEntries: 3
# CHECK32-NEXT: NumberOfRelocationEntries: 5
# CHECK32-NEXT: LengthOfImportFileIDStringTable: 365
# CHECK32-NEXT: NumberOfImportFileIDs: 1
# CHECK32-NEXT: OffsetToImportFileIDs: 0xa4
# CHECK32-NEXT: LengthOfStringTable: 24
# CHECK32-NEXT: OffsetToStringTable: 0x211

# CHECK64: ---File Header:
# CHECK64-NEXT: Magic: 0x1f7
# CHECK64-NEXT: NumberOfSections: 1
# CHECK64-NEXT: Timestamp: None (0)
# CHECK64-NEXT: SymbolTableOffset: 0x0
# CHECK64-NEXT: SymbolTableEntries: 0
# CHECK64-NEXT: OptionalHeaderSize: 0x0
# CHECK64-NEXT: Flags: 0x0

# CHECK64: ---Loader Section Header:
# CHECK64-NEXT: Version: 2
# CHECK64-NEXT: NumberOfSymbolEntries: 3
# CHECK64-NEXT: NumberOfRelocationEntries: 5
# CHECK64-NEXT: LengthOfImportFileIDStringTable: 365
# CHECK64-NEXT: NumberOfImportFileIDs: 1
# CHECK64-NEXT: OffsetToImportFileIDs: 0xd0
# CHECK64-NEXT: LengthOfStringTable: 35
# CHECK64-NEXT: OffsetToStringTable: 0x23d
# CHECK64-NEXT: OffsetToSymbolTable 0x38
# CHECK64-NEXT: OffsetToRelocationEntries 0x80
41 changes: 41 additions & 0 deletions llvm/tools/llvm-objdump/XCOFFDump.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,7 @@ class XCOFFDumper : public objdump::Dumper {
void printPrivateHeaders() override;
void printFileHeader();
void printAuxiliaryHeader();
void printLoaderSectionHeader();
void printAuxiliaryHeader(const XCOFFAuxiliaryHeader32 *AuxHeader);
void printAuxiliaryHeader(const XCOFFAuxiliaryHeader64 *AuxHeader);
template <typename AuxHeaderMemberType, typename XCOFFAuxiliaryHeader>
Expand All @@ -66,6 +67,7 @@ class XCOFFDumper : public objdump::Dumper {
void XCOFFDumper::printPrivateHeaders() {
printFileHeader();
printAuxiliaryHeader();
printLoaderSectionHeader();
}

FormattedString XCOFFDumper::formatName(StringRef Name) {
Expand Down Expand Up @@ -262,6 +264,45 @@ void XCOFFDumper::printAuxiliaryHeader(
AuxSize, *AuxHeader);
}

void XCOFFDumper::printLoaderSectionHeader() {
Expected<uintptr_t> LoaderSectionAddrOrError =
Obj.getSectionFileOffsetToRawData(XCOFF::STYP_LOADER);
if (!LoaderSectionAddrOrError) {
reportUniqueWarning(LoaderSectionAddrOrError.takeError());
return;
}
uintptr_t LoaderSectionAddr = LoaderSectionAddrOrError.get();

if (LoaderSectionAddr == 0)
return;

auto PrintLoadSecHeaderCommon = [&](const auto *LDHeader) {
printNumber("Version:", LDHeader->Version);
printNumber("NumberOfSymbolEntries:", LDHeader->NumberOfSymTabEnt);
printNumber("NumberOfRelocationEntries:", LDHeader->NumberOfRelTabEnt);
printNumber("LengthOfImportFileIDStringTable:",
LDHeader->LengthOfImpidStrTbl);
printNumber("NumberOfImportFileIDs:", LDHeader->NumberOfImpid);
printHex("OffsetToImportFileIDs:", LDHeader->OffsetToImpid);
printNumber("LengthOfStringTable:", LDHeader->LengthOfStrTbl);
printHex("OffsetToStringTable:", LDHeader->OffsetToStrTbl);
};

Width = 35;
outs() << "\n---Loader Section Header:\n";
if (Obj.is64Bit()) {
const LoaderSectionHeader64 *LoaderSec64 =
reinterpret_cast<const LoaderSectionHeader64 *>(LoaderSectionAddr);
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Is there a risk that the data won't be aligned in memory, such that on some architectures, reading the data will cause a failure?

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@diggerlin diggerlin Jan 14, 2025 •
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If I understand your question correctly. I wrote following test case and run , it do not crash. it looks the PowerPC do not need to be alignment on the memory in when reading the data.

bash> cat test.cpp
unsigned int var =10;
int main() {
 char *cvar = reinterpret_cast<char *>(&var)+1;

 int *us = reinterpret_cast<int *>(cvar);
 (*us)++;
 return *us;
}

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Yes, I think you understood the question correctly, but you've missed the fact that this code could be run on non-PowerPC architectures, which is where my concern lies. See issues like #95811 for examples.

In this case, perhaps we should check that LoaderSectionAddr is appropriately aligned and emit an error if it isn't. Alternatively, we can simply do a memcpy of the raw data into a local copy of LoaderSectionHeader[64|32], so that the data is guaranteed to be aligned. I think either approach is valid, since it's probably a requirement (either explicitly, or indirectly implied by other aspects of the spec) of the XCOFF spec that LoaderSectionAddr is aligned.

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I think it only happen when compile with option -mstrict-align on the AArch64, I do not think llvm compile the llvm-objdump with option -mstrict-align.

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I've seen issues fixed in LLVM because of alignment problems, flagged by build bots. The issue I filed was just one possible example. Another example: 8fbe1e7.

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@diggerlin diggerlin Jan 16, 2025 •
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There is a lot of reinterpret_cast or static_cast in the XCOFFObjectFile.cpp/Archive.cpp etc. it will have the same problem if there is.
I think if we want to fix the problem we need to have underlying API to deal with the problem for whole the llvm in a separate patch instead of using memcpy one by one.

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In an unrelated PR, a comment was made that some (all?) Elf_* type reading already uses that API. See #118739 (comment), so this may be a solution.

Anyway, I agree that since this is a potentially wider issue, we can ignore it for now.

PrintLoadSecHeaderCommon(LoaderSec64);
printHex("OffsetToSymbolTable", LoaderSec64->OffsetToSymTbl);
printHex("OffsetToRelocationEntries", LoaderSec64->OffsetToRelEnt);
} else {
const LoaderSectionHeader32 *LoaderSec32 =
reinterpret_cast<const LoaderSectionHeader32 *>(LoaderSectionAddr);
PrintLoadSecHeaderCommon(LoaderSec32);
}
}

void XCOFFDumper::printFileHeader() {
Width = 20;
outs() << "\n---File Header:\n";
Expand Down
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