add note on self modifying code and flush cache

Cargo.toml

@@ -17,6 +17,7 @@ path = "src/lib.rs"
 name = "tpom"
 path = "src/bin.rs"
 [dependencies]
+cacheflush-sys = "0.1.0"
 ctor = "0.2.6"
 goblin = "0.6.0"
 libc = "0.2.151"

src/vdso.rs

@@ -4,6 +4,7 @@ use goblin::strtab::Strtab;
 use core::slice;
 use std::error::Error;
 use std::fs;
+use cacheflush_sys;
 
 #[derive(Debug, PartialEq)]
 pub(crate) struct DynSym {
@@ -115,11 +116,10 @@ impl vDSO {
         // We need to clear the instruction cache, otherwise it's possible that the old
         // instructions (the trampoline) get executed with the new data (the original vDSO
         // function)
+        self.change_mode(false);
         unsafe {
-            //doesn't exist ((
-            //libc::cacheflush(dst_addr, opcodes.len(), libc::BCACHE);
+            cacheflush_sys::flush(dst_addr as *const u8, opcodes.len());
         }
-        self.change_mode(false);
     }
 
     pub fn entry(&self, wanted: Kind) -> Option<impl TVDSOFun + '_> {