haskell · zlonast · Aug 24, 2026
diff --git a/Cabal/src/Distribution/Simple/GHC/Internal.hs b/Cabal/src/Distribution/Simple/GHC/Internal.hs
@@ -597,6 +597,7 @@ linkGhcOptions verbosity lbi bi clbi =
               (mkVersion [9, 4])
               (compiler lbi)
               (maybeToFlag $ programPath <$> lookupProgram gppProgram (withPrograms lbi))
+        , ghcOptAsProgram = maybeToFlag $ programPath <$> lookupProgram gccProgram (withPrograms lbi)
         }
   where
     exe_paths =

diff --git a/Cabal/src/Distribution/Simple/Program/GHC.hs b/Cabal/src/Distribution/Simple/Program/GHC.hs
@@ -532,6 +532,8 @@ data GhcOptions = GhcOptions
   -- ^ Program to use for the C compiler; the @ghc -pgmc@ flag.
   , ghcOptGppProgram :: Flag FilePath
   -- ^ Program to use for the C++ compiler; the @ghc -pgmcxx@ flag.
+  , ghcOptAsProgram :: Flag FilePath
+  -- ^ Program to use for the Assembler; the @ghc -pgma@ flag.
   , ----------------------------
     -- Language and extensions
 
@@ -889,6 +891,7 @@ renderGhcOptions comp _platform@(Platform _arch os) opts
         , ["-opta" ++ opt | opt <- ghcOptAsmOptions opts]
         , concat [["-pgmc", cc] | cc <- flag ghcOptCcProgram]
         , concat [["-pgmcxx", cxx] | cxx <- flag ghcOptGppProgram]
+        , concat [["-pgma", as] | as <- flag ghcOptAsProgram]
         , -----------------
           -- Linker stuff
 

diff --git a/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/Main.hs b/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/Main.hs
@@ -0,0 +1,15 @@
+{-# LANGUAGE ForeignFunctionInterface #-}
+
+module Main where
+
+import Foreign.C (CInt (..))
+
+foreign import ccall "pgma.h meaning_of_life_asm"
+  meaning_of_life_asm :: IO CInt
+
+main :: IO ()
+main = do
+  secret <- meaning_of_life_asm
+  if secret == 33
+    then putStrLn ("The secret is " ++ show secret)
+    else error ("Expected value 33, got " ++ show secret)
diff --git a/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/README.md b/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/README.md
@@ -0,0 +1,7 @@
+# ForeignOptsPgma
+
+This test case asserts that cabal passes the `-pgma` GHC option to override the assembler program.
+
+The cabal file sets `ghc-options: -pgma scripts/as-wrapper.sh`, pointing GHC at a shell script wrapper (`scripts/as-wrapper.sh`) instead of the system assembler program. The wrapper adds `--defsym meaning_of_life_val=33` to every compilation and then delegates to the real `as`. The assembler source requires `meaning_of_life_val` to be defined; if the wrapper is not used as the assembler program, the build fails.
+
+This test is skipped on Windows (no POSIX shell).
diff --git a/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/abits/asmlib_aarch64_darwin.S b/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/abits/asmlib_aarch64_darwin.S
@@ -0,0 +1,11 @@
+    # macOS/AArch64 (Mach-O)
+    .macro  func name
+    .globl _\name
+_\name:
+    .endm
+
+    .text
+    func meaning_of_life_asm
+
+    mov     w0, #MEANING_OF_LIFE_VAL
+    ret
diff --git a/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/abits/asmlib_x86_64_darwin.asm b/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/abits/asmlib_x86_64_darwin.asm
@@ -0,0 +1,6 @@
+section .text
+global meaning_of_life_asm
+
+meaning_of_life_asm:
+    mov eax, meaning_of_life_val 
+    ret
diff --git a/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/abits/asmlib_x86_64_linux.S b/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/abits/asmlib_x86_64_linux.S
@@ -0,0 +1,7 @@
+        .text
+        .globl meaning_of_life_asm
+        .type meaning_of_life_asm, @function
+meaning_of_life_asm:
+        movl    $MEANING_OF_LIFE_VAL, %eax
+        ret
+        .size meaning_of_life_asm, .-meaning_of_life_asm
diff --git a/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/abits/asmlib_x86_64_windows.S b/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/abits/asmlib_x86_64_windows.S
@@ -0,0 +1,6 @@
+        .text
+        .globl meaning_of_life_asm
+
+meaning_of_life_asm:
+        movl    $MEANING_OF_LIFE_VAL, %eax
+        ret
diff --git a/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/abits/pgma.h b/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/abits/pgma.h
@@ -0,0 +1,6 @@
+#ifndef PGMALIB_H
+#define PGMALIB_H
+
+int meaning_of_life_asm();
+
+#endif
diff --git a/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/cabal.out b/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/cabal.out
diff --git a/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/cabal.project b/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/cabal.project
@@ -0,0 +1 @@
+packages: .
diff --git a/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/cabal.test.hs b/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/cabal.test.hs
@@ -0,0 +1,8 @@
+import Test.Cabal.Prelude
+
+main = do
+  cabalTest $ recordMode DoNotRecord $ do
+    cwd <- fmap testCurrentDir getTestEnv
+    let wrapper = cwd </> "scripts/as-wrapper.sh"
+    cabal "v2-build" ["foreign-opts-pgma-exe"]
+    withPlan $ runPlanExe "foreign-opts-pgma" "foreign-opts-pgma-exe" []
diff --git a/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/foreign-opts-pgma.cabal b/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/foreign-opts-pgma.cabal
@@ -0,0 +1,20 @@
+cabal-version:       3.0
+name:                foreign-opts-pgma
+version:             0.1
+build-type:          Simple
+
+executable foreign-opts-pgma-exe
+  main-is:             Main.hs
+  build-depends:       base
+  default-language:    Haskell2010
+  include-dirs:        abits
+  if os(windows)
+    asm-sources:       abits/asmlib_x86_64_windows.S
+  elif os(darwin)
+    asm-sources:       abits/asmlib_x86_64_darwin.asm
+    asm-options:       -d meaning_of_life_val=33
+  elif os(aarch64)
+    asm-sources:       abits/asmlib_aarch64_darwin.S
+  elif os(linux)
+    asm-sources:       abits/asmlib_x86_64_linux.S
+  ghc-options:         -pgma scripts/as-wrapper.sh
diff --git a/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/scripts/as-wrapper.sh b/cabal-testsuite/PackageTests/FFI/ForeignOptsPgma/scripts/as-wrapper.sh
@@ -0,0 +1,4 @@
+#!/bin/sh
+# Wrapper around `as` that adds --d meaning_of_life_val=33 to every compilation.
+# Used by the ForeignOptsPgma test to verify that -pgma selects this wrapper.
+exec nasm -f macho64 "$@"
diff --git a/cabal-testsuite/PackageTests/ShowBuildInfo/Complex/single.out b/cabal-testsuite/PackageTests/ShowBuildInfo/Complex/single.out
diff --git a/cabal-testsuite/src/Test/Cabal/OutputNormalizer.hs b/cabal-testsuite/src/Test/Cabal/OutputNormalizer.hs
@@ -15,7 +15,7 @@ import Data.Array ((!))
 import Text.Regex.Base
 import Text.Regex.TDFA
 
-import qualified Data.Foldable as F
+import Data.Foldable qualified as F
 
 normalizeOutput :: NormalizerEnv -> String -> String
 normalizeOutput nenv =
@@ -138,6 +138,10 @@ normalizeOutput nenv =
         . resub
           "\"-pgmcxx\",\"[^\"]+\""
           "\"-pgmcxx\",\"<CXXCPATH>\""
+        -- Normalize the assembler compiler path embedded in -pgma.
+        . resub
+          "\"-pgma\",\"[^\"]+\""
+          "\"-pgma\",\"<ASPATH>\""
         -- Remove cabal version output from show-build-info output
         . resub
           ("{\"cabal-lib-version\":\"" ++ posixRegexEscape (display (normalizerCabalVersion nenv)) ++ "\"")

diff --git a/changelog.d/11764.md b/changelog.d/11764.md
@@ -0,0 +1,8 @@
+---
+synopsis: Add explicit `pgma` flag for GHC invocation
+packages: [Cabal]
+prs: 11764
+---
+Add an explicit `pgma` flag to Cabal's GHC invocation logic. Pass the assembler
+program explicitly to GHC. This change allows users to specify a custom `as`
+program to compile assembly manually.