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fix(build): route TH to ghc-iserv-dyn to bypass truncated libHSghc.a

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Root cause: libHSghc-9.10.3-5702.a (287,768,576 bytes) has its last AR
entry (Expr.o) claiming 517,544 bytes but only 82,258 bytes remain —
the archive is truncated. GHC's internal readAr (Data.Binary.Get) panics
at position 287,686,318 when it tries to read the full claimed size.

The truncated .a is read lazily: IHP's TH splices queue a dependency on
the ghc package, which flushes to readAr after all 477 modules compile.
This explains the invariant crash at [477 of 477] WidgetVersionInclude.

ghc-iserv-dyn is not exposed in ghc-with-packages/bin/ (why
-fexternal-interpreter alone silently fell back to the internal linker).
Use -pgmi with the absolute path in the unwrapped GHC store to force
iserv-dyn, which uses dlopen on libHSghc.so (intact, 110 MB) instead
of readAr on the truncated .a. No crash.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
tegwick 2026-05-02 11:11:07 +02:00
parent accfec84ec
commit 11ff61c1ba
1 changed files with 12 additions and 0 deletions
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flake.nix
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@ -127,6 +127,18 @@
"--disable-split-sections"
"--ghc-option=-j1"
"--disable-shared"
# GHC 9.10.3 bug: libHSghc-9.10.3-5702.a is truncated (last AR
# entry Expr.o claims 517544 bytes but only 82258 remain).
# GHC's internal static linker (readAr via Data.Binary.Get) panics
# after all 477 modules compile when it flushes deferred symbol
# loads from IHP's TH splices that transitively need the ghc pkg.
# Fix: delegate TH evaluation to ghc-iserv-dyn, which uses dlopen
# on libHSghc.so (intact) instead of readAr on the truncated .a.
# ghc-iserv-dyn is not in ghc-with-packages/bin/, so use -pgmi
# with the absolute path in the unwrapped GHC store path.
"--ghc-option=-fexternal-interpreter"
"--ghc-option=-pgmi"
"--ghc-option=${hprev.ghc}/lib/ghc-9.10.3/bin/ghc-iserv-dyn"
];
postUnpack = (old.postUnpack or "") + ''
_actual="$sourceRoot/build/Generated/ActualTypes.hs"