Merge pull request #16977 from kcbanner/lib_getauxval_fixup

linux: export getauxval when not compiling with libc

Author: kubkon

lib/std/os/linux.zig

@@ -154,8 +154,22 @@ pub usingnamespace @import("linux/io_uring.zig");
 /// Set by startup code, used by `getauxval`.
 pub var elf_aux_maybe: ?[*]std.elf.Auxv = null;
 
-/// See `std.elf` for the constants.
-pub fn getauxval(index: usize) usize {
+pub usingnamespace if (switch (builtin.zig_backend) {
+    // Calling extern functions is not yet supported with these backends
+    .stage2_x86_64, .stage2_aarch64, .stage2_arm, .stage2_riscv64, .stage2_sparc64 => false,
+    else => !builtin.link_libc,
+}) struct {
+    /// See `std.elf` for the constants.
+    /// This matches the libc getauxval function.
+    pub extern fn getauxval(index: usize) usize;
+    comptime {
+        @export(getauxvalImpl, .{ .name = "getauxval", .linkage = .Weak });
+    }
+} else struct {
+    pub const getauxval = getauxvalImpl;
+};
+
+fn getauxvalImpl(index: usize) callconv(.C) usize {
     const auxv = elf_aux_maybe orelse return 0;
     var i: usize = 0;
     while (auxv[i].a_type != std.elf.AT_NULL) : (i += 1) {