swung0x48 834a8917ff [MG_Backend, docs] (P7): a transport with no record arm stops by name instead of dying mid-frame ...

P3b/P4b espryt D1 slice 5, landing under the P7 program (notes/p7/PLAN-PH-P34B-P7.md
§1.2 row "g_fboTextureSyncList", §3 wave 2-D).

ResolveFramebufferSubsystemArm and its three siblings classify a family's arm as Handles,
Legacy or NoArm and stop only on NoArm. Under an active transport Legacy is not a slower
answer, it is a postponed crash: all four pre-handle arms reach frontend state through
accessors that are BARRIER_PULLED rows (FieldOwnership.def), and under a transport that
state belongs to a client that is no longer parked behind this apply, so the accessor's
honest answer is Fatal{UnmigratedPipeInput, "<field>@<verb>"} on the first verb that reaches
it. That is the audit's own claim about g_fboTextureSyncList - "separation-safe, because the
record arm returns first" - which holds only while the record arm is ARMED, and nothing
checked that.

Each of the four now stops, under #if MOBILEGL_BUILD_DISAGGREGATED, when the transport is
not monolith and the verdict is not Handles, through one shared
StopOnTransportWithoutRecordArm(bit, detail) that formats both causes and hands them to
BufferImpl::StopOnArmlessPipeSubsystem - this file's existing single voice for "the
configuration left no arm to run". A transport with the record arm off IS that condition
with a different cause: the legacy arm is present but unreachable. Reusing the voice keeps
the census's family word and puts the cause in the message rather than in a new word the
census would have to learn.

Said precisely, this is a RESOLVE-TIME stop and not a startup one. The four resolvers are
function-local statics resolved lazily at first use, deliberately - Managers.cpp's own
comment says a stop inside eglMakeCurrent reads to the harness as "no usable GPU" and skips
- so the stop still lands in a scenario body where ctest reports it. What it no longer does
is wait for a verb to dereference the client's state and then blame the accessor.

Red-once (R-16), and it is the safety argument the audit asserted but never ran:
MOBILEGL_PIPE_PUSH=0x1dff (the Handles lane's 0x1fff minus 0x200,
kMGPipeSubsystemFramebuffer) with MOBILEGL_TRANSPORT=inproc, running
ClearThenReadPixelsScenario.ClearWithNoDrawIsVisibleToDefaultFramebufferReadPixels. Both
runs abort; what changes is what the abort says. Without the stop:
Fatal{UnmigratedPipeInput, "GetFramebufferBindingSlot@Clear"} - mid-frame, naming an
accessor and a verb, with nothing pointing at the mask. With it:
Fatal{PipeLegacyMemosDisabled, "MOBILEGL_TRANSPORT is not monolith and
kMGPipeSubsystemFramebuffer (bit 9) is clear (or refused), so the record arm is off and the
legacy arm is unreachable: ..."}.

Gates: integration-split 202/202, integration-spawn 118/118, integration-tcp 121/121,
ctest -L unit 2408/2408, integration-magma-split 73/73, spawn_lane_parity / fatal_census (79
sites, 0 unmarked) / link_ratchet (186, unchanged) green, G1 .text 0xa52203 with both nm
lists byte-identical - the four blocks are inside MOBILEGL_BUILD_DISAGGREGATED and the pull
build compiles none of them.

2026-09-22 16:41:54 -04:00

..

Disaggregated

[MG_Backend, docs] (P7): a transport with no record arm stops by name instead of dying mid-frame

2026-09-22 16:41:54 -04:00