lib.systems: add various has* flags useful for embedded systems

NixOS · Dec 7, 2024 · e76ac5d · e76ac5d
1 parent 2b4c300
commit e76ac5d
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Showing 3 changed files with 112 additions and 39 deletions.
diff --git a/lib/systems/default.nix b/lib/systems/default.nix
@@ -193,6 +193,34 @@ let
          || isWasm                                                     # WASM
         ) && !isStatic;
 
+      # Whether the system provides its own libunwind implementation that we
+      # should use.
+      hasSystemLibunwind = final.isFreeBSD || final.isDarwin;
+
+      # Controls whether stack unwinding support is enabled.
+      hasStackUnwinding = !(final.isWasm || final.isNone);
+
+      # You often don't want exceptions in an embedded setting, disable them by default.
+      hasExceptions = !(final.isNone || final.isWasm);
+
+      # If there is no kernel (`isNone`) we assume no threads. WASM can
+      # supposedly support threads in certain cases, so this might change in
+      # the future.
+      hasThreads = !(final.isNone || final.isWasm);
+
+      # On bare metal platforms or on WASM there is no "obvious" filesystem to
+      # access, so disable support by default. (Use-cases like filesystem
+      # emulation with WASI or accessing an SD card over SPI need more
+      # configuration than just being able to work "by default".)
+      hasFilesystem = !(final.isNone || final.isWasm);
+
+      # Wanting localization in embedded settings is probably a rare edge-case,
+      # so disable it by default.
+      hasLocalization = !final.isNone;
+
+      # Without a kernel there is no cross-platform way for libc to obtain a clock.
+      hasMonotonicClock = !final.isNone;
+
       # The difference between `isStatic` and `hasSharedLibraries` is mainly the
       # addition of the `staticMarker` (see make-derivation.nix).  Some
       # platforms, like embedded machines without a libc (e.g. arm-none-eabi)

diff --git a/pkgs/development/compilers/llvm/common/default.nix b/pkgs/development/compilers/llvm/common/default.nix
@@ -742,23 +742,28 @@ let
           bintools = bintools';
           extraPackages =
             [ targetLlvmLibraries.compiler-rt ]
-            ++ lib.optionals (!stdenv.targetPlatform.isWasm && !stdenv.targetPlatform.isFreeBSD) [
-              targetLlvmLibraries.libunwind
-            ];
+            ++ lib.optionals
+              (stdenv.targetPlatform.hasStackUnwinding && !stdenv.targetPlatform.hasSystemLibunwind)
+              [
+                targetLlvmLibraries.libunwind
+              ];
           extraBuildCommands =
             lib.optionalString (lib.versions.major metadata.release_version == "13") (
               ''
                 echo "-rtlib=compiler-rt -Wno-unused-command-line-argument" >> $out/nix-support/cc-cflags
                 echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
               ''
-              + lib.optionalString (!stdenv.targetPlatform.isWasm) ''
+              + lib.optionalString stdenv.targetPlatform.hasStackUnwinding ''
                 echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
                 echo "-L${targetLlvmLibraries.libunwind}/lib" >> $out/nix-support/cc-ldflags
               ''
-              + lib.optionalString (!stdenv.targetPlatform.isWasm && stdenv.targetPlatform.useLLVM or false) ''
-                echo "-lunwind" >> $out/nix-support/cc-ldflags
-              ''
-              + lib.optionalString stdenv.targetPlatform.isWasm ''
+              +
+                lib.optionalString
+                  (stdenv.targetPlatform.hasStackUnwinding && stdenv.targetPlatform.useLLVM or false)
+                  ''
+                    echo "-lunwind" >> $out/nix-support/cc-ldflags
+                  ''
+              + lib.optionalString (!stdenv.targetPlatform.hasExceptions) ''
                 echo "-fno-exceptions" >> $out/nix-support/cc-cflags
               ''
             )
@@ -772,16 +777,30 @@ let
               "-B${targetLlvmLibraries.compiler-rt}/lib"
             ]
             ++ lib.optional (
-              !stdenv.targetPlatform.isWasm && !stdenv.targetPlatform.isFreeBSD
+              stdenv.targetPlatform.hasStackUnwinding
+              && (
+                !stdenv.targetPlatform.hasSystemLibunwind
+                # TODO: Why is this flag needed on Darwin, but not on FreeBSD?
+                || stdenv.targetPlatform.isDarwin
+              )
             ) "--unwindlib=libunwind"
             ++ lib.optional (
-              !stdenv.targetPlatform.isWasm
-              && !stdenv.targetPlatform.isFreeBSD
+              stdenv.targetPlatform.hasStackUnwinding
+              && (
+                !stdenv.targetPlatform.hasSystemLibunwind
+                # TODO: Why is this flag needed on Darwin, but not on FreeBSD?
+                || stdenv.targetPlatform.isDarwin
+              )
               && stdenv.targetPlatform.useLLVM or false
             ) "-lunwind"
-            ++ lib.optional stdenv.targetPlatform.isWasm "-fno-exceptions";
+            ++ lib.optional (!stdenv.targetPlatform.hasExceptions) "-fno-exceptions";
           nixSupport.cc-ldflags = lib.optionals (
-            !stdenv.targetPlatform.isWasm && !stdenv.targetPlatform.isFreeBSD
+            stdenv.targetPlatform.hasStackUnwinding
+            && (
+              !stdenv.targetPlatform.hasSystemLibunwind
+              # TODO: Why is this flag needed on Darwin, but not on FreeBSD?
+              || stdenv.targetPlatform.isDarwin
+            )
           ) [ "-L${targetLlvmLibraries.libunwind}/lib" ];
         }
       );
@@ -794,9 +813,7 @@ let
           extraPackages =
             [ targetLlvmLibraries.compiler-rt-no-libc ]
             ++ lib.optionals
-              (
-                !stdenv.targetPlatform.isWasm && !stdenv.targetPlatform.isFreeBSD && !stdenv.targetPlatform.isDarwin
-              )
+              (stdenv.targetPlatform.hasStackUnwinding && !stdenv.targetPlatform.hasSystemLibunwind)
               [
                 targetLlvmLibraries.libunwind
               ];
@@ -806,14 +823,27 @@ let
                 echo "-rtlib=compiler-rt -Wno-unused-command-line-argument" >> $out/nix-support/cc-cflags
                 echo "-B${targetLlvmLibraries.compiler-rt-no-libc}/lib" >> $out/nix-support/cc-cflags
               ''
-              + lib.optionalString (!stdenv.targetPlatform.isWasm && !stdenv.targetPlatform.isDarwin) ''
-                echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
-                echo "-L${targetLlvmLibraries.libunwind}/lib" >> $out/nix-support/cc-ldflags
-              ''
-              + lib.optionalString (!stdenv.targetPlatform.isWasm && stdenv.targetPlatform.useLLVM or false) ''
-                echo "-lunwind" >> $out/nix-support/cc-ldflags
-              ''
-              + lib.optionalString stdenv.targetPlatform.isWasm ''
+              +
+                lib.optionalString
+                  (
+                    stdenv.targetPlatform.hasStackUnwinding
+                    && (
+                      !stdenv.targetPlatform.hasSystemLibunwind
+                      # TODO: Why is this flag needed on FreeBSD, but not on Darwin?
+                      || stdenv.targetPlatform.isFreeBSD
+                    )
+                  )
+                  ''
+                    echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
+                    echo "-L${targetLlvmLibraries.libunwind}/lib" >> $out/nix-support/cc-ldflags
+                  ''
+              +
+                lib.optionalString
+                  (stdenv.targetPlatform.hasStackUnwinding && stdenv.targetPlatform.useLLVM or false)
+                  ''
+                    echo "-lunwind" >> $out/nix-support/cc-ldflags
+                  ''
+              + lib.optionalString (!stdenv.targetPlatform.hasExceptions) ''
                 echo "-fno-exceptions" >> $out/nix-support/cc-cflags
               ''
             )
@@ -827,16 +857,20 @@ let
               "-B${targetLlvmLibraries.compiler-rt-no-libc}/lib"
             ]
             ++ lib.optional (
-              !stdenv.targetPlatform.isWasm && !stdenv.targetPlatform.isFreeBSD && !stdenv.targetPlatform.isDarwin
+              stdenv.targetPlatform.hasStackUnwinding && !stdenv.targetPlatform.hasSystemLibunwind
             ) "--unwindlib=libunwind"
             ++ lib.optional (
-              !stdenv.targetPlatform.isWasm
-              && !stdenv.targetPlatform.isFreeBSD
+              stdenv.targetPlatform.hasStackUnwinding
+              && (
+                !stdenv.targetPlatform.hasSystemLibunwind
+                # TODO: Why is this flag needed on Darwin, but not on FreeBSD?
+                || stdenv.targetPlatform.isDarwin
+              )
               && stdenv.targetPlatform.useLLVM or false
             ) "-lunwind"
-            ++ lib.optional stdenv.targetPlatform.isWasm "-fno-exceptions";
+            ++ lib.optional (!stdenv.targetPlatform.hasExceptions) "-fno-exceptions";
           nixSupport.cc-ldflags = lib.optionals (
-            !stdenv.targetPlatform.isWasm && !stdenv.targetPlatform.isFreeBSD && !stdenv.targetPlatform.isDarwin
+            stdenv.targetPlatform.hasStackUnwinding && !stdenv.targetPlatform.hasSystemLibunwind
           ) [ "-L${targetLlvmLibraries.libunwind}/lib" ];
         }
       );
@@ -863,7 +897,7 @@ let
               "-nostdlib++"
             ]
             ++ lib.optional (
-              lib.versionAtLeast metadata.release_version "15" && stdenv.targetPlatform.isWasm
+              lib.versionAtLeast metadata.release_version "15" && !stdenv.targetPlatform.hasExceptions
             ) "-fno-exceptions";
         }
       );
@@ -888,7 +922,7 @@ let
               "-B${targetLlvmLibraries.compiler-rt-no-libc}/lib"
             ]
             ++ lib.optional (
-              lib.versionAtLeast metadata.release_version "15" && stdenv.targetPlatform.isWasm
+              lib.versionAtLeast metadata.release_version "15" && !stdenv.targetPlatform.hasExceptions
             ) "-fno-exceptions";
         }
       );
@@ -909,7 +943,7 @@ let
           nixSupport.cc-cflags =
             [ "-nostartfiles" ]
             ++ lib.optional (
-              lib.versionAtLeast metadata.release_version "15" && stdenv.targetPlatform.isWasm
+              lib.versionAtLeast metadata.release_version "15" && !stdenv.targetPlatform.hasExceptions
             ) "-fno-exceptions";
         }
       );
@@ -925,7 +959,7 @@ let
           extraBuildCommands = mkExtraBuildCommands0 cc;
         }
         // lib.optionalAttrs (
-          lib.versionAtLeast metadata.release_version "15" && stdenv.targetPlatform.isWasm
+          lib.versionAtLeast metadata.release_version "15" && !stdenv.targetPlatform.hasExceptions
         ) { nixSupport.cc-cflags = [ "-fno-exceptions" ]; };
 
       # Aliases

diff --git a/pkgs/development/compilers/llvm/common/libcxx/default.nix b/pkgs/development/compilers/llvm/common/libcxx/default.nix
@@ -54,18 +54,23 @@ let
 
   cxxabiCMakeFlags = lib.optionals (lib.versionAtLeast release_version "18") [
     "-DLIBCXXABI_USE_LLVM_UNWINDER=OFF"
-  ] ++ lib.optionals (useLLVM && !stdenv.hostPlatform.isWasm) (if lib.versionAtLeast release_version "18" then [
+  ] ++ lib.optionals (useLLVM && stdenv.targetPlatform.hasStackUnwinding) (if lib.versionAtLeast release_version "18" then [
     "-DLIBCXXABI_ADDITIONAL_LIBRARIES=unwind"
-    "-DLIBCXXABI_USE_COMPILER_RT=ON"
   ] else [
-    "-DLIBCXXABI_USE_COMPILER_RT=ON"
     "-DLIBCXXABI_USE_LLVM_UNWINDER=ON"
-  ]) ++ lib.optionals stdenv.hostPlatform.isWasm [
+  ]) ++ lib.optionals (useLLVM && !stdenv.targetPlatform.isWasm) [
+    "-DLIBCXXABI_USE_COMPILER_RT=ON"
+  ] ++ lib.optionals (!stdenv.targetPlatform.hasThreads) [
     "-DLIBCXXABI_ENABLE_THREADS=OFF"
+  ] ++ lib.optionals (!stdenv.targetPlatform.hasExceptions) [
     "-DLIBCXXABI_ENABLE_EXCEPTIONS=OFF"
   ] ++ lib.optionals (!enableShared || stdenv.hostPlatform.isWindows) [
     # Required on Windows due to https://github.com/llvm/llvm-project/issues/55245
     "-DLIBCXXABI_ENABLE_SHARED=OFF"
+  ] ++ lib.optionals (!stdenv.targetPlatform.hasLocalization) [
+    "-DLIBCXX_ENABLE_LOCALIZATION=OFF"
+  ] ++ lib.optionals (!stdenv.targetPlatform.hasMonotonicClock) [
+    "-DLIBCXX_ENABLE_MONOTONIC_CLOCK=OFF"
   ];
 
   cxxCMakeFlags = [
@@ -90,9 +95,11 @@ let
     "-DLIBCXX_USE_COMPILER_RT=ON"
   ] ++ lib.optionals (useLLVM && !stdenv.hostPlatform.isFreeBSD && lib.versionAtLeast release_version "16") [
     "-DLIBCXX_ADDITIONAL_LIBRARIES=unwind"
-  ] ++ lib.optionals stdenv.hostPlatform.isWasm [
+  ] ++ lib.optionals (!stdenv.targetPlatform.hasThreads) [
     "-DLIBCXX_ENABLE_THREADS=OFF"
+  ] ++ lib.optionals (!stdenv.targetPlatform.hasFilesystem) [
     "-DLIBCXX_ENABLE_FILESYSTEM=OFF"
+  ] ++ lib.optionals (!stdenv.targetPlatform.hasExceptions) [
     "-DLIBCXX_ENABLE_EXCEPTIONS=OFF"
   ] ++ lib.optionals stdenv.hostPlatform.isWindows [
     # https://github.com/llvm/llvm-project/issues/55245
@@ -135,7 +142,11 @@ stdenv.mkDerivation (rec {
     ++ lib.optional (cxxabi != null) lndir;
 
   buildInputs = [ cxxabi ]
-    ++ lib.optionals (useLLVM && !stdenv.hostPlatform.isWasm && !stdenv.hostPlatform.isFreeBSD) [ libunwind ];
+    ++ lib.optionals (stdenv.targetPlatform.hasStackUnwinding && (
+        !stdenv.targetPlatform.hasSystemLibunwind
+        # TODO: Why is this needed on Darwin, but not on FreeBSD?
+        || stdenv.targetPlatform.isDarwin
+      ) && useLLVM) [ libunwind ];
 
   # libc++.so is a linker script which expands to multiple libraries,
   # libc++.so.1 and libc++abi.so or the external cxxabi. ld-wrapper doesn't