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cc-wrapper: conditionalize the nonexistent sysroot hack #213738

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cc-wrapper: conditionalize the nonexistent sysroot hack #213738

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0490c09
build-support/cc-wrapper: pass in non-existent --sysroot= to untangle…
trofi Jan 10, 2023
20e2ac9
cc-wrapper: conditionalize the nonexistent sysroot hack
Jan 31, 2023
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9 changes: 9 additions & 0 deletions pkgs/build-support/cc-wrapper/default.nix
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@
, isGNU ? false, isClang ? cc.isClang or false, gnugrep ? null
, buildPackages ? {}
, libcxx ? null
, enableNonExistentSysroot ? false
}:

with lib;
Expand Down Expand Up @@ -343,10 +344,18 @@ stdenv.mkDerivation {
# compile, because it uses "#include_next <limits.h>" to find the
# limits.h file in ../includes-fixed. To remedy the problem,
# another -idirafter is necessary to add that directory again.
#
# We use --sysroot=/nix/store/does/not/exist to drop embedded default
# path to glibc headers gcc was built against. Without it -idirafter
# only appends to the list and outdated glibc headers end up being
# used. 'cc-cflags-before' is used to allow user's --sysroot= option
# to override our default.
+ optionalString (libc != null) (''
touch "$out/nix-support/libc-cflags"
touch "$out/nix-support/libc-ldflags"
echo "-B${libc_lib}${libc.libdir or "/lib/"}" >> $out/nix-support/libc-crt1-cflags
'' + optionalString enableNonExistentSysroot ''
echo "--sysroot=/nix/store/does/not/exist" >> $out/nix-support/cc-cflags-before
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As stated in #213185 blanket --sysroot= changes library search path in transitive libraries. As a result we get linkage failures in dmd, d-seams, llvmPackages_rocm.compiler-rt. Conditional or not it's breaking real packages. The intent in the comment was only attempting to change header search path and not library search path.

For just headers there is an -isysroot flag. But it has it's own caveats as blanket --sysroot= also exposed failures in ipxe and wimboot. Those show that existing -idirafter sequence is incorrectly overridden in nixpkgs. It has to be fixed by chaning a priority.

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The conditional is only enabled for xgcc, which is never used to compile any of those packages.

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My suggestion would be to explore ways to add the flag locally to the place where it's intended to be used instead of changing the driver. I still think it's too heavy a hammer even for gcc.

'' + optionalString (!(cc.langD or false)) ''
echo "-idirafter ${libc_dev}${libc.incdir or "/include"}" >> $out/nix-support/libc-cflags
'' + optionalString (isGNU && (!(cc.langD or false))) ''
Expand Down