createdump: use 47-bit-valid SpecialDiagInfo address on arm64 macOS#130443
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The legacy macOS SpecialDiagInfo address 0x7fffffff10000000 is above Apple Silicon's 47-bit user-space VM limit, so lldb's MachO core reader refuses to return the segment and SOS reports "Special diagnostics info read failed". Write the segment at the 47-bit-valid 0x00007ffffff10000 on arm64 macOS (the same address already used on Linux 64-bit) while keeping the legacy address on x86_64 macOS. This is the createdump-side counterpart to dotnet/diagnostics#5823, whose reader probes both the new and legacy addresses so older dumps remain readable. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: f5c2b675-e04f-4544-8338-ab6dc4701d7f
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Pull request overview
This PR adjusts the fixed virtual address used for the “SpecialDiagInfo” dump segment on Apple Silicon macOS so it stays within the 47-bit user-space address range accepted by lldb’s Mach-O core reader, while preserving the legacy address on x86_64 macOS.
Changes:
- Use a 47-bit-valid
SpecialDiagInfoAddresson macOS arm64 (0x00007ffffff10000). - Keep the legacy macOS x86_64
SpecialDiagInfoAddressunchanged (0x7fffffff10000000).
hoyosjs
approved these changes
Jul 10, 2026
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noahfalk
approved these changes
Jul 10, 2026
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Summary
Fixes the createdump (write) side of the SpecialDiagInfo issue addressed on the
reader side in dotnet/diagnostics#5823.
On Apple Silicon, the legacy macOS SpecialDiagInfo address
0x7fffffff10000000is above the 47-bit user-space VM limit. createdump still writes a segment at
that address, but lldb's MachO core reader refuses to return reads above
0x7FFF_FFFFFFFF, so SOS reports:Special diagnostics info read failedand falls through to the slower managed-side path (or fails outright on older
builds without that fallback).
Change
src/coreclr/debug/createdump/specialdiaginfo.hnow selects the address by archon macOS:
0x00007ffffff10000(47-bit valid; same address alreadyused on Linux/other 64-bit)
0x7fffffff10000000(legacy, unchanged)All other platforms (Linux/other 64-bit, 32-bit) are unchanged.
The matching diagnostics reader (dotnet/diagnostics#5823) probes both the new
and legacy addresses, so dumps produced by older createdump binaries remain
readable — no regression.
Notes
SpecialThreadInfoAddress(0x7fffffff00000000) is intentionally left as-is;it's out of scope for this fix and lldb tolerates that region.
Note
This PR description was drafted with GitHub Copilot.