Inject missing #include <errno.h> into zlib

[hmenke]

This has suddently started failing when building on NixOS 25.11.

gzread.c:24:5: error: use of undeclared identifier 'errno'
   24 |     errno = 0;
      |     ^~~~~
gzread.c:36:13: error: use of undeclared identifier 'errno'
   36 |         if (errno == EAGAIN || errno == EWOULDBLOCK) {
      |             ^~~~~
gzread.c:36:22: error: use of undeclared identifier 'EAGAIN'
   36 |         if (errno == EAGAIN || errno == EWOULDBLOCK) {
      |                      ^~~~~~
gzread.c:36:32: error: use of undeclared identifier 'errno'
   36 |         if (errno == EAGAIN || errno == EWOULDBLOCK) {
      |                                ^~~~~
gzread.c:36:41: error: use of undeclared identifier 'EWOULDBLOCK'
   36 |         if (errno == EAGAIN || errno == EWOULDBLOCK) {
      |                                         ^~~~~~~~~~~
5 errors generated.

[CyberShadow]

started failing

I don't understand how this can be possible. We pin our Flake inputs..?

Do you mean if you update the Flake inputs to use the latest nixpkgs?

[hmenke]

Sorry, I guess I should have mentioned that I override the flake input like so

nix build .#btdu-static-x86_64 --override-input nixpkgs "github:NixOS/nixpkgs/nixos-25.11"

[CyberShadow]

Thanks. This seems like an upstream bug, have you checked if it has been reported to zlib? Do other projects apply similar patches?

[hmenke]

zlib blames the builder (madler/zlib#1126) and indeed I can see a build failure in configure.log

=== ztest30.c ===
#include <string.h>
#include <errno.h>
int main() { return strlen(strerror(errno)); }
===
/nix/store/zq0z7g2s1jnks1995nmp8ii6lp0xh6wq-clang-21.1.7/bin/clang --target=x86_64-unknown-linux-musl -isystem /nix/store/4vdrxsxq45rw02pmxizrzqpl67kjfl4v-musl-static-x86_64-unknown-linux-musl-1.2.5-dev/include -flto=thin -O2 -U_FORTIFY_SOURCE -w -fPIC -D_LARGEFILE64_SOURCE=1 -fuse-ld=lld -L/nix/store/6z8maf3yjcz2cm5m0fvrj15h3gn14i1x-musl-static-x86_64-unknown-linux-musl-1.2.5/lib -o ztest30 ztest30.c
ld.lld: error: cannot open Scrt1.o: No such file or directory
ld.lld: error: cannot open crti.o: No such file or directory
ld.lld: error: cannot open crtbeginS.o: No such file or directory
ld.lld: error: unable to find library -lgcc
ld.lld: error: unable to find library -lgcc_s
ld.lld: error: unable to find library -lgcc
ld.lld: error: unable to find library -lgcc_s
ld.lld: error: cannot open crtendS.o: No such file or directory
ld.lld: error: cannot open crtn.o: No such file or directory
clang: error: linker command failed with exit code 1 (use -v to see invocation)
(exit code 1)
Checking for strerror... No.

[hmenke]

Okay, the actual problem is that the compiler as it's configured currently cannot compile any executable. Attempting to compile a file with just an empty main in the Nix sandbox

echo "int main() {}" > test.c
$CC $CFLAGS -o test test.c $LDFLAGS

fails with

ld.lld: error: cannot open Scrt1.o: No such file or directory
ld.lld: error: cannot open crti.o: No such file or directory
ld.lld: error: cannot open crtbeginS.o: No such file or directory
ld.lld: error: unable to find library -lgcc
ld.lld: error: unable to find library -lgcc_s
ld.lld: error: unable to find library -lgcc
ld.lld: error: unable to find library -lgcc_s
ld.lld: error: cannot open crtendS.o: No such file or directory
ld.lld: error: cannot open crtn.o: No such file or directory
clang: error: linker command failed with exit code 1 (use -v to see invocation)

[CyberShadow]

Makes sense, the setup is pretty much only to support the specific cross build we need, so regular program compilation might be broken, but maybe we should fix that to make configure happy.

[hmenke]

This seems to work.

diff --git a/flake.nix b/flake.nix
index 7c7eb1b..406509e 100644
--- a/flake.nix
+++ b/flake.nix
@@ -144,7 +144,7 @@
               configurePhase = ''
                 # Use musl headers and disable glibc's FORTIFY_SOURCE
                 # Note: -w suppresses all warnings, needed because zlib's configure checks for any stderr output
-                export CC="${pkgs.llvmPackages.clang-unwrapped}/bin/clang --target=${targetTriple}"
+                export CC="${pkgs.llvmPackages.clang-unwrapped}/bin/clang --target=${targetTriple} -nostdlib"
                 export AR="${pkgs.llvmPackages.bintools-unwrapped}/bin/llvm-ar"
                 export RANLIB="${pkgs.llvmPackages.bintools-unwrapped}/bin/llvm-ranlib"
                 export CFLAGS="-isystem ${muslLibc.dev}/include -flto=thin -O2 -U_FORTIFY_SOURCE -w"