Gate FDE finder under features

Cargo.toml

@@ -6,12 +6,16 @@ edition = "2018"
 
 [dependencies]
 gimli = { version = "0.25.0", default-features = false, features = ["read"] }
-libc = "0.2"
+libc = { version = "0.2", optional = true }
 once_cell = { version = "1.8", optional = true }
 spin = { version = "0.9", default-features = false, features = ["lazy", "mutex", "spin_mutex"] }
 
 [features]
 std = ["once_cell"]
+alloc = []
+fde-phdr = ["libc"]
+fde-registry = ["alloc"]
+default = ["fde-phdr"]
 
 [profile.release]
 debug = true

src/find_fde/mod.rs

@@ -1,4 +1,6 @@
+#[cfg(feature = "fde-phdr")]
 mod phdr;
+#[cfg(feature = "fde-registry")]
 mod registry;
 
 use crate::util::*;
@@ -19,9 +21,11 @@ pub struct GlobalFinder(());
 
 impl FDEFinder for GlobalFinder {
     fn find_fde(&self, pc: usize) -> Option<FDESearchResult> {
+        #[cfg(feature = "fde-registry")]
         if let Some(v) = registry::get_finder().find_fde(pc) {
             return Some(v);
         }
+        #[cfg(feature = "fde-phdr")]
         if let Some(v) = phdr::get_finder().find_fde(pc) {
             return Some(v);
         }

src/lib.rs

@@ -5,6 +5,7 @@
 #![warn(unsafe_op_in_unsafe_fn)]
 #![cfg_attr(not(feature = "std"), no_std)]
 
+#[cfg(feature = "alloc")]
 extern crate alloc;
 
 mod abi;