gnu: build settings for _FILE_OFFSET_BITS=64

(backport <rust-lang#4345>)
(cherry picked from commit a184436)

Author: snogge

build.rs

@@ -13,6 +13,8 @@ const ALLOWED_CFGS: &'static [&'static str] = &[
     "freebsd13",
     "freebsd14",
     "freebsd15",
+    // Corresponds to `_FILE_OFFSET_BITS=64` in glibc
+    "gnu_file_offset_bits64",
     // FIXME(ctest): this config shouldn't be needed but ctest can't parse `const extern fn`
     "libc_const_extern_fn",
     "libc_deny_warnings",
@@ -44,6 +46,10 @@ fn main() {
     let (rustc_minor_ver, _is_nightly) = rustc_minor_nightly();
     let rustc_dep_of_std = env::var("CARGO_FEATURE_RUSTC_DEP_OF_STD").is_ok();
     let libc_ci = env::var("LIBC_CI").is_ok();
+    let target_env = env::var("CARGO_CFG_TARGET_ENV").unwrap_or_default();
+    let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap_or_default();
+    let target_ptr_width = env::var("CARGO_CFG_TARGET_POINTER_WIDTH").unwrap_or_default();
+    let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap_or_default();
 
     // The ABI of libc used by std is backward compatible with FreeBSD 12.
     // The ABI of libc from crates.io is backward compatible with FreeBSD 11.
@@ -85,6 +91,23 @@ fn main() {
     if linux_time_bits64 {
         set_cfg("linux_time_bits64");
     }
+    println!("cargo:rerun-if-env-changed=RUST_LIBC_UNSTABLE_GNU_FILE_OFFSET_BITS");
+    match env::var("RUST_LIBC_UNSTABLE_GNU_FILE_OFFSET_BITS") {
+        Ok(val) if val == "64" => {
+            if target_env == "gnu"
+                && target_os == "linux"
+                && target_ptr_width == "32"
+                && target_arch != "riscv32"
+                && target_arch != "x86_64"
+            {
+                set_cfg("gnu_file_offset_bits64");
+            }
+        }
+        Ok(val) if val != "32" => {
+            panic!("RUST_LIBC_UNSTABLE_GNU_FILE_OFFSET_BITS may only be set to '32' or '64'")
+        }
+        _ => {}
+    }
 
     // On CI: deny all warnings
     if libc_ci {

libc-test/build.rs

@@ -3664,6 +3664,26 @@ fn test_vxworks(target: &str) {
     cfg.generate(src_hotfix_dir().join("lib.rs"), "main.rs");
 }
 
+fn config_gnu_bits(target: &str, cfg: &mut ctest::TestGenerator) {
+    match env::var("RUST_LIBC_UNSTABLE_GNU_FILE_OFFSET_BITS") {
+        Ok(val) if val == "64" => {
+            if target.contains("gnu")
+                && target.contains("linux")
+                && !target.ends_with("x32")
+                && !target.contains("riscv32")
+                && env::var("CARGO_CFG_TARGET_POINTER_WIDTH").unwrap() == "32"
+            {
+                cfg.define("_FILE_OFFSET_BITS", Some("64"));
+                cfg.cfg("gnu_file_offset_bits64", None);
+            }
+        }
+        Ok(val) if val != "32" => {
+            panic!("RUST_LIBC_UNSTABLE_GNU_FILE_OFFSET_BITS may only be set to '32' or '64'")
+        }
+        _ => {}
+    }
+}
+
 fn test_linux(target: &str) {
     assert!(target.contains("linux"));
 
@@ -3707,6 +3727,8 @@ fn test_linux(target: &str) {
     // glibc versions older than 2.29.
     cfg.define("__GLIBC_USE_DEPRECATED_SCANF", None);
 
+    config_gnu_bits(target, &mut cfg);
+
     headers! { cfg:
                "ctype.h",
                "dirent.h",
@@ -4869,6 +4891,7 @@ fn test_linux_like_apis(target: &str) {
     if linux || android || emscripten {
         // test strerror_r from the `string.h` header
         let mut cfg = ctest_cfg();
+        config_gnu_bits(target, &mut cfg);
         cfg.skip_type(|_| true).skip_static(|_| true);
 
         headers! { cfg: "string.h" }
@@ -4885,6 +4908,7 @@ fn test_linux_like_apis(target: &str) {
         // test fcntl - see:
         // http://man7.org/linux/man-pages/man2/fcntl.2.html
         let mut cfg = ctest_cfg();
+        config_gnu_bits(target, &mut cfg);
 
         if musl {
             cfg.header("fcntl.h");
@@ -4914,6 +4938,7 @@ fn test_linux_like_apis(target: &str) {
     if (linux && !wali) || android {
         // test termios
         let mut cfg = ctest_cfg();
+        config_gnu_bits(target, &mut cfg);
         cfg.header("asm/termbits.h");
         cfg.header("linux/termios.h");
         cfg.skip_type(|_| true)
@@ -4938,6 +4963,7 @@ fn test_linux_like_apis(target: &str) {
     if linux || android {
         // test IPV6_ constants:
         let mut cfg = ctest_cfg();
+        config_gnu_bits(target, &mut cfg);
         headers! {
             cfg:
             "linux/in6.h"
@@ -4969,6 +4995,7 @@ fn test_linux_like_apis(target: &str) {
         // "resolve.h" defines a `p_type` macro that expands to `__p_type`
         // making the tests for these fails when both are included.
         let mut cfg = ctest_cfg();
+        config_gnu_bits(target, &mut cfg);
         cfg.header("elf.h");
         cfg.skip_fn(|_| true)
             .skip_static(|_| true)
@@ -4988,6 +5015,7 @@ fn test_linux_like_apis(target: &str) {
     if (linux && !wali) || android {
         // Test `ARPHRD_CAN`.
         let mut cfg = ctest_cfg();
+        config_gnu_bits(target, &mut cfg);
         cfg.header("linux/if_arp.h");
         cfg.skip_fn(|_| true)
             .skip_static(|_| true)