diff --git a/pkgs/development/compilers/gcc/8/default.nix b/pkgs/development/compilers/gcc/8/default.nix
index f5572c077f31..129ca72251fc 100644
--- a/pkgs/development/compilers/gcc/8/default.nix
+++ b/pkgs/development/compilers/gcc/8/default.nix
@@ -373,6 +373,9 @@ stdenv.mkDerivation ({
       stdenv.lib.platforms.freebsd ++
       stdenv.lib.platforms.illumos ++
       stdenv.lib.platforms.darwin;
+
+    # See #40038
+    broken = stdenv.isDarwin;
   };
 }
 
diff --git a/pkgs/development/compilers/iasl/default.nix b/pkgs/development/compilers/iasl/default.nix
index b1b31aecae13..ab9fd23f5088 100644
--- a/pkgs/development/compilers/iasl/default.nix
+++ b/pkgs/development/compilers/iasl/default.nix
@@ -1,4 +1,4 @@
-{stdenv, fetchurl, bison, flex}:
+{stdenv, fetchurl, fetchpatch, bison, flex}:
 
 stdenv.mkDerivation rec {
   pname = "iasl";
@@ -9,12 +9,20 @@ stdenv.mkDerivation rec {
     sha256 = "1vgqlv9pvxc52faxixpgz7hi1awqmj88bw5vqn3bldf6fmkh147w";
   };
 
-  NIX_CFLAGS_COMPILE = "-O3";
+  NIX_CFLAGS_COMPILE = [
+    "-O3"
+  ];
 
   buildFlags = "iasl";
 
   buildInputs = [ bison flex ];
 
+  patches = fetchpatch {
+    /* https://github.com/acpica/acpica/pull/389 */
+    url = "https://github.com/acpica/acpica/commit/935ca65f7806a3ef9bd02a947e50f3a1f586ac67.patch";
+    sha256 = "0jz4bakifphm425shbd1j99hldgy71m7scl8mwibm441d56l3ydf";
+  };
+
   installPhase =
     ''
       install -d $out/bin
diff --git a/pkgs/development/compilers/nasm/default.nix b/pkgs/development/compilers/nasm/default.nix
index 8d92bc4eba2f..f5645ae02192 100644
--- a/pkgs/development/compilers/nasm/default.nix
+++ b/pkgs/development/compilers/nasm/default.nix
@@ -20,6 +20,8 @@ stdenv.mkDerivation rec {
     make golden && make test
   '';
 
+  NIX_CFLAGS_COMPILE="-Wno-error=attributes";
+
   meta = with stdenv.lib; {
     homepage = https://www.nasm.us/;
     description = "An 80x86 and x86-64 assembler designed for portability and modularity";
diff --git a/pkgs/development/libraries/libglvnd/default.nix b/pkgs/development/libraries/libglvnd/default.nix
index 2b64d5b7220a..b976c9c36b83 100644
--- a/pkgs/development/libraries/libglvnd/default.nix
+++ b/pkgs/development/libraries/libglvnd/default.nix
@@ -25,6 +25,8 @@ stdenv.mkDerivation rec {
     "-UDEFAULT_EGL_VENDOR_CONFIG_DIRS"
     # FHS paths are added so that non-NixOS applications can find vendor files.
     "-DDEFAULT_EGL_VENDOR_CONFIG_DIRS=\"${addOpenGLRunpath.driverLink}/share/glvnd/egl_vendor.d:/etc/glvnd/egl_vendor.d:/usr/share/glvnd/egl_vendor.d\""
+
+    "-Wno-error=array-bounds"
   ] ++ lib.optional stdenv.cc.isClang "-Wno-error";
 
   # Indirectly: https://bugs.freedesktop.org/show_bug.cgi?id=35268
diff --git a/pkgs/development/libraries/libomxil-bellagio/default.nix b/pkgs/development/libraries/libomxil-bellagio/default.nix
index 7c14d8102fbe..4d45c6872e4c 100644
--- a/pkgs/development/libraries/libomxil-bellagio/default.nix
+++ b/pkgs/development/libraries/libomxil-bellagio/default.nix
@@ -16,6 +16,10 @@ stdenv.mkDerivation rec {
 
   doCheck = false; # fails
 
+  # Fix for #40213, probably permanent, because upstream doesn't seem to be
+  # developed anymore. Alternatively, gcc7Stdenv could be used.
+  NIX_CFLAGS_COMPILE = "-Wno-error=array-bounds";
+
   meta = with stdenv.lib; {
     homepage = https://sourceforge.net/projects/omxil/;
     description = "An opensource implementation of the Khronos OpenMAX Integration Layer API to access multimedia components";
diff --git a/pkgs/development/tools/misc/elfutils/default.nix b/pkgs/development/tools/misc/elfutils/default.nix
index 7a3579f0635d..99e751043beb 100644
--- a/pkgs/development/tools/misc/elfutils/default.nix
+++ b/pkgs/development/tools/misc/elfutils/default.nix
@@ -10,12 +10,21 @@ stdenv.mkDerivation rec {
     sha256 = "08qhrl4g6qqr4ga46jhh78y56a47p3msa5b2x1qhzbxhf71lfmzb";
   };
 
-  patches = [ ./debug-info-from-env.patch ];
-
   postPatch = ''
     patchShebangs tests
   '';
 
+  patches = [
+    ./debug-info-from-env.patch
+
+    /* For gcc8. Fixes -Werror=packed-not-aligned errors.
+    incorporated in upstream, so can probably be removed at next update */
+    (fetchurl {
+      url = http://git.openembedded.org/openembedded-core/plain/meta/recipes-devtools/elfutils/files/0001-Ensure-that-packed-structs-follow-the-gcc-memory-lay.patch?id=49aae1d75ff1c6a9643c30a8cc5776a2ffa83dd3;
+      sha256 = "11sg2dn3vjvgq2fb9n8pgw1ajvs3gliks7djg1794wxlfg0rvifb";
+    })
+  ];
+
   hardeningDisable = [ "format" ];
 
   # We need bzip2 in NativeInputs because otherwise we can't unpack the src,
diff --git a/pkgs/os-specific/linux/systemd/default.nix b/pkgs/os-specific/linux/systemd/default.nix
index 4117df8cf13c..48f915214188 100644
--- a/pkgs/os-specific/linux/systemd/default.nix
+++ b/pkgs/os-specific/linux/systemd/default.nix
@@ -15,9 +15,13 @@
 , withKexectools ? lib.any (lib.meta.platformMatch stdenv.hostPlatform) kexectools.meta.platforms, kexectools
 }:
 
-stdenv.mkDerivation {
-  version = "242";
+let
+  pythonLxmlEnv = buildPackages.python3Packages.python.withPackages ( ps: with ps; [ python3Packages.lxml ]);
+
+in stdenv.mkDerivation rec {
   pname = "systemd";
+  # To whoever updates this to 239: check the todo on line 173.
+  version = "242";
 
   # When updating, use https://github.com/systemd/systemd-stable tree, not the development one!
   # Also fresh patches should be cherry-picked from that tree to our current one.
diff --git a/pkgs/tools/networking/dhcp/default.nix b/pkgs/tools/networking/dhcp/default.nix
index 24e23e6e0d33..bcf0743b7b9e 100644
--- a/pkgs/tools/networking/dhcp/default.nix
+++ b/pkgs/tools/networking/dhcp/default.nix
@@ -39,7 +39,10 @@ stdenv.mkDerivation rec {
     (lib.optional stdenv.isLinux "--with-randomdev=/dev/random")
   ] ++ stdenv.lib.optionals (openldap != null) [ "--with-ldap" "--with-ldapcrypto" ];
 
-  NIX_CFLAGS_COMPILE = [ "-Wno-error=pointer-compare" ];
+  NIX_CFLAGS_COMPILE = [
+    "-Wno-error=pointer-compare"
+    "-Wno-error=format-truncation"
+  ];
 
   installFlags = [ "DESTDIR=\${out}" ];
 
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 4ac7927bf8a5..7d25977bd14c 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -3772,6 +3772,7 @@ in
   };
 
   hdf5 = callPackage ../tools/misc/hdf5 {
+    stdenv = gcc7Stdenv;
     gfortran = null;
     szip = null;
     mpi = null;
@@ -7519,7 +7520,8 @@ in
   gerbil-unstable = callPackage ../development/compilers/gerbil/unstable.nix { stdenv = gccStdenv; };
 
   gccFun = callPackage ../development/compilers/gcc/7;
-  gcc = gcc7;
+  # Temporary solution until #40038 is fixed
+  gcc = if stdenv.isDarwin then gcc7 else gcc8;
   gcc-unwrapped = gcc.cc;
 
   gccStdenv = if stdenv.cc.isGNU then stdenv else stdenv.override {
@@ -8171,7 +8173,9 @@ in
     buildLlvmTools = buildPackages.llvmPackages_6.tools;
     targetLlvmLibraries = targetPackages.llvmPackages_6.libraries;
   } // stdenv.lib.optionalAttrs (stdenv.cc.isGNU && stdenv.hostPlatform.isi686) {
-    stdenv = gcc6Stdenv; # with gcc-7: undefined reference to `__divmoddi4'
+    # with gcc-7 on i686: undefined reference to `__divmoddi4'
+    # Failing tests with gcc8.
+    stdenv = overrideCC stdenv (if stdenv.hostPlatform.isi686 then gcc6 else gcc7);
   });
 
   llvmPackages_7 = callPackage ../development/compilers/llvm/7 ({