From 80f5e0b661ea3edc5ec893e4fda1dd576086cede Mon Sep 17 00:00:00 2001
From: David Rusu <davidrusu.me@gmail.com>
Date: Sun, 7 Jun 2026 03:28:47 -0400
Subject: [PATCH] fix: link glibc C23 strtoul/strtoll compat shim for static
 linking

The prebuilt iden3 rapidsnark archives are compiled on a glibc >= 2.38 host
(Ubuntu 24.04 / GCC 13), whose headers redirect strtoll/strtoull to the C23
interceptor symbols __isoc23_strtoll / __isoc23_strtoull. When the static
archives (static-rapidsnark feature) are linked on a host with an older glibc
(e.g. glibc 2.35), those symbols are undefined and linking fails:

  rust-lld: error: undefined symbol: __isoc23_strtoull

Compile thin forwarders to the classic strtoll/strtoull symbols and link them
via whole-archive so the static path resolves regardless of the host glibc
version. Gated to the static feature on glibc-Linux; the shared library and
all other targets are unaffected.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 crates/build.rs        | 23 +++++++++++++++++++++++
 crates/isoc23_compat.c | 24 ++++++++++++++++++++++++
 2 files changed, 47 insertions(+)
 create mode 100644 crates/isoc23_compat.c

diff --git a/crates/build.rs b/crates/build.rs
index 39819cc..345c04f 100644
--- a/crates/build.rs
+++ b/crates/build.rs
@@ -71,6 +71,29 @@ fn main() {
     // Android bundles pthread into libc
     let thread_lib = if is_android_target() { "c" } else { "pthread" };
     println!("cargo:rustc-link-lib={thread_lib}");
+
+    // glibc >= 2.38 redirects strtoll/strtoull to the C23 interceptor symbols
+    // __isoc23_strtoll / __isoc23_strtoull. The prebuilt iden3 rapidsnark archives
+    // were compiled against such a glibc, so when they are linked statically on a
+    // host with an older glibc (e.g. glibc 2.35) the verifier objects reference
+    // __isoc23_* symbols that do not exist there and linking fails. Compile thin
+    // forwarders to the classic strtoll/strtoull and link them so the static path
+    // resolves regardless of the host glibc version. Only relevant for the static
+    // archive on glibc-Linux; the shared library and other targets are unaffected.
+    println!("cargo:rerun-if-changed=isoc23_compat.c");
+    if is_static_rapidsnark()
+        && env::var("CARGO_CFG_TARGET_OS").as_deref() == Ok("linux")
+        && env::var("CARGO_CFG_TARGET_ENV").as_deref() == Ok("gnu")
+    {
+        cc::Build::new()
+            .file("isoc23_compat.c")
+            .cargo_metadata(false)
+            .compile("isoc23_compat");
+        println!("cargo:rustc-link-search=native={out_dir}");
+        // whole-archive so the forwarders are included unconditionally, regardless
+        // of this archive's position relative to librapidsnark.a on the link line.
+        println!("cargo:rustc-link-lib=static:+whole-archive=isoc23_compat");
+    }
 }
 
 fn is_static_rapidsnark() -> bool {
diff --git a/crates/isoc23_compat.c b/crates/isoc23_compat.c
new file mode 100644
index 0000000..a7f32e0
--- /dev/null
+++ b/crates/isoc23_compat.c
@@ -0,0 +1,24 @@
+/*
+ * glibc >= 2.38 redirects strtoll/strtoull to the C23 interceptor symbols
+ * __isoc23_strtoll / __isoc23_strtoull at compile time. The prebuilt iden3
+ * rapidsnark archives were compiled against such a glibc, so their verifier
+ * objects reference those symbols. When the static archives are linked on a
+ * host with an older glibc (e.g. Ubuntu 22.04 / glibc 2.35) the symbols are
+ * undefined and linking fails.
+ *
+ * Provide thin forwarders to the classic strtoll/strtoull symbols. We bind to
+ * the legacy symbol names explicitly via asm labels and deliberately avoid
+ * including <stdlib.h>, so this translation unit is itself immune to the C23
+ * header redirect (otherwise the forwarder would recurse into itself when this
+ * file is compiled on a new-glibc build host).
+ */
+extern long long __legacy_strtoll(const char *, char **, int) __asm__("strtoll");
+extern unsigned long long __legacy_strtoull(const char *, char **, int) __asm__("strtoull");
+
+long long __isoc23_strtoll(const char *nptr, char **endptr, int base) {
+    return __legacy_strtoll(nptr, endptr, base);
+}
+
+unsigned long long __isoc23_strtoull(const char *nptr, char **endptr, int base) {
+    return __legacy_strtoull(nptr, endptr, base);
+}