find libc and zig std lib at runtime

this removes the following configure options:
 * ZIG_LIBC_LIB_DIR
 * ZIG_LIBC_STATIC_LIB_DIR
 * ZIG_LIBC_INCLUDE_DIR
 * ZIG_DYNAMIC_LINKER
 * ZIG_EACH_LIB_RPATH
 * zig's reliance on CMAKE_INSTALL_PREFIX

these options are still available as command line options, however,
the default will attempt to execute the system's C compiler to
collect system defaults for these values.

closes #870

1 files changed, 38 insertions, 6 deletions

diff --git a/src/link.cpp b/src/link.cpp
index f0537ffa0f..57fa59b675 100644
--- a/src/link.cpp
+++ b/src/link.cpp
@@ -164,6 +164,34 @@ static void add_rpath(LinkJob *lj, Buf *rpath) {
     lj->rpath_table.put(rpath, true);
 }
 
+static Buf *get_dynamic_linker_path(CodeGen *g) {
+    if (g->is_native_target && g->zig_target.arch.arch == ZigLLVM_x86_64) {
+        const char *cc_exe = getenv("CC");
+        cc_exe = (cc_exe == nullptr) ? "cc" : cc_exe;
+        ZigList<const char *> args = {};
+        args.append("-print-file-name=ld-linux-x86-64.so.2");
+        Termination term;
+        Buf *out_stderr = buf_alloc();
+        Buf *out_stdout = buf_alloc();
+        int err;
+        if ((err = os_exec_process(cc_exe, args, &term, out_stderr, out_stdout))) {
+            return target_dynamic_linker(&g->zig_target);
+        }
+        if (term.how != TerminationIdClean || term.code != 0) {
+            return target_dynamic_linker(&g->zig_target);
+        }
+        if (buf_ends_with_str(out_stdout, "\n")) {
+            buf_resize(out_stdout, buf_len(out_stdout) - 1);
+        }
+        if (buf_len(out_stdout) == 0 || buf_eql_str(out_stdout, "ld-linux-x86-64.so.2")) {
+            return target_dynamic_linker(&g->zig_target);
+        }
+        return out_stdout;
+    } else {
+        return target_dynamic_linker(&g->zig_target);
+    }
+}
+
 static void construct_linker_job_elf(LinkJob *lj) {
     CodeGen *g = lj->codegen;
 
@@ -259,12 +287,16 @@ static void construct_linker_job_elf(LinkJob *lj) {
         lj->args.append(buf_ptr(g->libc_static_lib_dir));
     }
 
-    if (g->dynamic_linker && buf_len(g->dynamic_linker) > 0) {
-        lj->args.append("-dynamic-linker");
-        lj->args.append(buf_ptr(g->dynamic_linker));
-    } else {
-        lj->args.append("-dynamic-linker");
-        lj->args.append(buf_ptr(target_dynamic_linker(&g->zig_target)));
+    if (!g->is_static) {
+        if (g->dynamic_linker != nullptr) {
+            assert(buf_len(g->dynamic_linker) != 0);
+            lj->args.append("-dynamic-linker");
+            lj->args.append(buf_ptr(g->dynamic_linker));
+        } else {
+            Buf *resolved_dynamic_linker = get_dynamic_linker_path(g);
+            lj->args.append("-dynamic-linker");
+            lj->args.append(buf_ptr(resolved_dynamic_linker));
+        }
     }
 
     if (shared) {