Polyfill the missing memchr impl in latest esp-hal

esp-mbedtls/Cargo.toml

@@ -23,12 +23,13 @@ cfg-if = "1.0.0"
 edge-nal = { version = "0.4.0", optional = true }
 critical-section = "1.1.3"
 crypto-bigint = { version = "0.5.3", optional = true, default-features = false, features = ["extra-sizes"] }
+tinyrlibc = { version = "0.5", optional = true, default-features = false }
 
 [features]
 default = ["edge-nal"]
 async = ["dep:embedded-io-async"]
 esp32 = ["esp-hal/esp32", "esp-wifi/esp32", "esp-mbedtls-sys/esp32", "crypto-bigint"]
-esp32c3 = ["esp-hal/esp32c3", "esp-wifi/esp32c3", "esp-mbedtls-sys/esp32c3", "crypto-bigint"]
+esp32c3 = ["esp-hal/esp32c3", "esp-wifi/esp32c3", "esp-mbedtls-sys/esp32c3", "crypto-bigint", "tinyrlibc/memchr"]
 esp32s2 = ["esp-hal/esp32s2", "esp-wifi/esp32s2", "esp-mbedtls-sys/esp32s2", "crypto-bigint"]
 esp32s3 = ["esp-hal/esp32s3", "esp-wifi/esp32s3", "esp-mbedtls-sys/esp32s3", "crypto-bigint"]
 

esp-mbedtls/src/esp_hal.rs

@@ -66,3 +66,13 @@ impl Drop for Tls<'_> {
         critical_section::with(|cs| SHARED_SHA.borrow_ref_mut(cs).take());
     }
 }
+
+// See https://github.com/esp-rs/esp-mbedtls/pull/62#issuecomment-2560830139
+// TODO: In future - and for all baremetal platforms - we should be having a definition like the one below
+// for **all** libc functions used by `mbedtls`
+//
+// And then each baremetal platform can decide to opt-in and use the definition(s)
+// from `tinyrlibc` or opt-out and provide their own implementation(s)
+#[cfg(feature = "esp32c3")]
+#[used]
+static _MEMCHR: unsafe extern "C" fn(*const core::ffi::c_void, core::ffi::c_int, usize) -> *const core::ffi::c_void = tinyrlibc::memchr;