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[Fix] (MG_Remote, Protocol): mark CapsSnapshot's four retired fields deprecated instead of deleting them - a deletion FREES the vtable slot, so callMask took slot 14 from an [int] vector as an 8-byte ulong with no ABI-major bump and a fingerprint that mixes struct sizes rather than the schema

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swung0x48
2026-09-11 15:04:54 -04:00
parent c5c12b489a
commit ed60c06b98
2 changed files with 21 additions and 5 deletions
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MobileGL/MG_Remote/Protocol/generated/protocol_generated.h
+2 -2
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@@ -822,8 +822,8 @@ struct CapsSnapshot FLATBUFFERS_FINAL_CLASS : private ::flatbuffers::Table {
VT_FORMATCAPS = 8,
VT_EXTENSIONS = 10,
VT_APIVERSION = 12,
VT_CALLMASK = 14,
VT_BACKENDTYPE = 16
VT_CALLMASK = 22,
VT_BACKENDTYPE = 24
};
const ::flatbuffers::Vector<uint8_t> *dynamicParameters() const {
return GetPointer<const ::flatbuffers::Vector<uint8_t> *>(VT_DYNAMICPARAMETERS);
MobileGL/MG_Remote/Protocol/protocol.fbs
+19 -3
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@@ -98,8 +98,8 @@ table Welcome {
// (plan B appendix A, `get_caps`). The three blobs are byte-for-byte images of
// the corresponding POD structs; they are versioned by structSize-first
// discipline, not by this schema.
// The four fields this table used to end with are DELETED (CONTRACT-P5 table 0,
// "CapsSnapshot redundancy"), not renamed and not deprecated:
// The four fields this table used to end with are RETIRED (CONTRACT-P5 table 0,
// "CapsSnapshot redundancy"):
//
// maxComputeWorkGroupCount / maxComputeWorkGroupSize - they ride inside
// `dynamicParameters` already (BackendObject.h:392-393), and two spellings of
@@ -112,13 +112,29 @@ table Welcome {
// prefersCpuXfbPrimitiveAccounting - answered by kCapCpuXfbPrimitiveAccounting
// in `callMask` below.
//
// They were the LAST four fields, so nothing before them moved a vtable slot.
// THEY ARE `(deprecated)`, NOT DELETED, AND THAT IS NOT A STYLE CHOICE. In
// FlatBuffers a table field's id IS its vtable slot, and REMOVING a field FREES
// that slot for the next field appended to the table - so plainly deleting these
// four would have handed slots 14 and 16, which used to carry `[int]` vectors
// (4-byte uoffsets), to `callMask` (an 8-byte inline ulong) and `backendType` (a
// 4-byte inline uint). Two peers straddling that edit both still announce
// abiMajor 1, and the ABI fingerprint mixes struct sizes and a git stamp, not the
// schema, so neither the handshake nor the fingerprint could see it: the reader
// would parse a uoffset as a ulong. `(deprecated)` keeps 14/18/20 burned, pushes
// the two new fields to 22/24, generates no accessor for the retired names so
// nothing can read or write them, and costs zero bytes on the wire. The
// alternative - bumping MOBILEGL_PROTOCOL_ABI_MAJOR - is a real break for a
// change that does not need to be one.
table CapsSnapshot {
dynamicParameters: [ubyte];
rendererInfo: [ubyte];
formatCaps: [ubyte];
extensions: [string];
apiVersion: string;
maxComputeWorkGroupCount: [int] (deprecated);
maxComputeWorkGroupSize: [int] (deprecated);
tableSlotMask: ulong (deprecated);
prefersCpuXfbPrimitiveAccounting: bool (deprecated);
// MGPCaps::CallMask (MGPipeTypes.h:127). Bits 0..8 are MGPCapBit; bits 32..47
// are the CONSUMER MASK - bit (32+n) means "the server has a consumer for
// MGPipe subsystem bit n" - and MG_Remote/CapsCodec.h holds the four constexprs