Add fixes for profiling

See IntersectMBO/plutus#7415 (comment)
See https://gitlab.haskell.org/ghc/ghc/-/merge_requests/15096

Author: hamishmack

overlays/bootstrap.nix

@@ -346,6 +346,12 @@ in {
 
                 ++ onWasm (until                "9.13" ./patches/ghc/ghc-9.12-wasm-shared-libs.patch)
                 ++ onWasm (until                "9.13" ./patches/ghc/ghc-9.12-wasm-keep-cafs.patch)
+
+                # See https://github.com/IntersectMBO/plutus/issues/7415#issuecomment-3531989244
+                ++ fromUntil "9.6" "9.9" ./patches/ghc/ghc-profiling-fix.patch
+
+                # See https://gitlab.haskell.org/ghc/ghc/-/merge_requests/15096
+                ++ fromUntil "9.6" "9.13" ./patches/ghc/ghc-16bit-elf-section-header-overflow.patch
                 ;
         in ({
             ghc8107 = traceWarnOld "8.10" (final.callPackage ../compiler/ghc {

overlays/patches/ghc/ghc-16bit-elf-section-header-overflow.patch

@@ -0,0 +1,34 @@
+From e90e136c16ef10fc47d339cf8964255a5131c9c9 Mon Sep 17 00:00:00 2001
+From: Luite Stegeman <stegeman@gmail.com>
+Date: Sat, 22 Nov 2025 15:05:37 +0100
+Subject: [PATCH] rts: Handle 16-bit overflow of ELF section header string
+ table
+
+If the section header string table is stored in a section greater
+than 65535, the 16-bit value e_shstrndx in the ELF header does not
+contain the section number, but rather an overflow value SHN_XINDEX
+indicating that we need to look elsewhere.
+
+This fixes the linker by not using e_shstrndx directly but calling
+elf_shstrndx, which correctly handles the overflow value.
+
+Fixes #26603
+---
+ rts/linker/Elf.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/rts/linker/Elf.c b/rts/linker/Elf.c
+index 85a56c120d49..0314abb0c68c 100644
+--- a/rts/linker/Elf.c
++++ b/rts/linker/Elf.c
+@@ -205,7 +205,7 @@ ocInit_ELF(ObjectCode * oc)
+     oc->info->sectionHeader = (Elf_Shdr *) ((uint8_t*)oc->image
+                                             + oc->info->elfHeader->e_shoff);
+     oc->info->sectionHeaderStrtab = (char*)((uint8_t*)oc->image +
+-            oc->info->sectionHeader[oc->info->elfHeader->e_shstrndx].sh_offset);
++            oc->info->sectionHeader[elf_shstrndx(oc->info->elfHeader)].sh_offset);
+ 
+     oc->n_sections = elf_shnum(oc->info->elfHeader);
+ 
+-- 
+GitLab

overlays/patches/ghc/ghc-profiling-fix.patch

@@ -0,0 +1,46 @@
+diff --git a/compiler/GHC/Core/Utils.hs b/compiler/GHC/Core/Utils.hs
+index 0453fb93af..84d2d9cfe5 100644
+--- a/compiler/GHC/Core/Utils.hs
++++ b/compiler/GHC/Core/Utils.hs
+@@ -79,7 +79,7 @@ import GHC.Core.Reduction
+ import GHC.Core.TyCon
+ import GHC.Core.Multiplicity
+ 
+-import GHC.Builtin.Names ( makeStaticName, unsafeEqualityProofIdKey )
++import GHC.Builtin.Names ( makeStaticName, unsafeEqualityProofIdKey, unsafeReflDataConKey )
+ import GHC.Builtin.PrimOps
+ 
+ import GHC.Types.Var
+@@ -328,6 +328,10 @@ mkTick t orig_expr = mkTick' id id orig_expr
+           -> CoreExpr
+   mkTick' top rest expr = case expr of
+ 
++    Case scrut bndr ty alts@[Alt ac abs _rhs]
++      | Just rhs <- isUnsafeEqualityCase scrut bndr alts
++      -> top $ mkTick' (\e -> Case scrut bndr ty [Alt ac abs e]) rest rhs
++
+     -- Cost centre ticks should never be reordered relative to each
+     -- other. Therefore we can stop whenever two collide.
+     Tick t2 e
+@@ -2676,3 +2680,21 @@ isUnsafeEqualityProof e
+   = v `hasKey` unsafeEqualityProofIdKey
+   | otherwise
+   = False
++
++isUnsafeEqualityCase :: CoreExpr -> Id -> [CoreAlt] -> Maybe CoreExpr
++-- See (U3) and (U4) in
++-- Note [Implementing unsafeCoerce] in base:Unsafe.Coerce
++isUnsafeEqualityCase scrut bndr alts
++  | [Alt ac _ rhs] <- alts
++  , DataAlt dc <- ac
++  , dc `hasKey` unsafeReflDataConKey
++  , isDeadBinder bndr
++      -- We can only discard the case if the case-binder is dead
++      -- It usually is, but see #18227
++  , Var v `App` _ `App` _ `App` _ <- scrut
++  , v `hasKey` unsafeEqualityProofIdKey
++      -- Check that the scrutinee really is unsafeEqualityProof
++      -- and not, say, error
++  = Just rhs
++  | otherwise
++  = Nothing