Crossgen2 Mach-O R2R output has LC_SEGMENT_64 filesize > vmsize, rejected by llvm-objdump/otool #124982
Description
Crossgen2 composite Mach-O R2R images have filesize > vmsize in the first LC_SEGMENT_64 load command. This causes llvm-objdump --macho and llvm-readobj to reject the file:
llvm-objdump: error: 'file.dll': truncated or malformed object
(load command 0 filesize field in LC_SEGMENT_64 greater than vmsize field)
The __data section extends past the segment's declared vmsize. For example, a small library produces vmsize=0x7A9 but filesize=0x9D9.
The runtime loads these images fine — this only affects tooling inspection.
Repro steps:
# On x64 Linux, cross-compile for osx-arm64
# Build clr for x64 (crossgen2 host) and arm64 (target JIT + libs)
./build.sh clr -c Release
./build.sh clr+libs -arch arm64 -c Release
# Crossgen2 any library as composite Mach-O for osx-arm64
dotnet exec artifacts/bin/coreclr/linux.x64.Release/crossgen2/crossgen2.dll \
--jitpath artifacts/bin/coreclr/linux.arm64.Release/libclrjit_universal_arm64_x64.so \
--targetarch arm64 --targetos osx \
-f macho --composite \
-r "artifacts/bin/microsoft.netcore.app.runtime.linux-arm64/Release/runtimes/linux-arm64/lib/net11.0/*.dll" \
-r "artifacts/bin/coreclr/linux.arm64.Release/IL/System.Private.CoreLib.dll" \
--out /tmp/test.macho.dll \
"artifacts/bin/microsoft.netcore.app.runtime.linux-arm64/Release/runtimes/linux-arm64/lib/net11.0/System.Buffers.dll"
# Output is valid Mach-O:
file /tmp/test.macho.dll
# Mach-O 64-bit arm64 object, flags:<|SUBSECTIONS_VIA_SYMBOLS>
# But llvm-objdump rejects it:
llvm-objdump --macho --section-headers /tmp/test.macho.dll
# error: truncated or malformed object (load command 0 filesize field
# in LC_SEGMENT_64 greater than vmsize field)