Read the auxv in library constructor

Having `putenv()` called overwrites the auxiliary vector, giving garbage
values for the vDSO base address and the page size.

Reading these values from the auxiliary constructor during the
startup phase, before any actual program code executes prevents the
issue.

The auxiliary vector is only read once and stored as a static variable.

Cargo.toml

@@ -17,8 +17,9 @@ path = "src/lib.rs"
 name = "tpom"
 path = "src/bin.rs"
 [dependencies]
+ctor = "0.2.6"
 goblin = "0.6.0"
-libc = "0.2.137"
+libc = "0.2.151"
 
 [dev-dependencies]
 serial_test = "0.9.0"

src/auxv.rs

@@ -1,6 +1,7 @@
 use std::error::Error;
+use ctor::ctor;
 
-#[derive(Debug)]
+#[derive(Debug, Copy, Clone)]
 pub struct AuxVecValues {
     pub(crate) vdso_base: usize,
     pub(crate) page_size: usize,
@@ -25,6 +26,11 @@ unsafe fn get_auxv_ptr() -> *const usize {
 }
 
 pub(crate) fn read_aux_vec() -> Result<AuxVecValues, Box<dyn Error>> {
+    Ok(*AUX)
+}
+//#[cfg_attr(any(target_os = "linux"), link_section = ".init_array")]
+#[ctor]
+static AUX: AuxVecValues = {
     // The auxiliary vector is an array of key:value tuples, represented as [usize, usize]
     // The end is delimited by having the key == AT_NULL
     let mut out = unsafe { get_auxv_ptr() };
@@ -43,9 +49,12 @@ pub(crate) fn read_aux_vec() -> Result<AuxVecValues, Box<dyn Error>> {
             out = out.offset(2);
         }
     }
-    if ptr == 0 || pagesize == 0 {
-        panic!("wtf");
+    if ptr == 0 {
+        panic!("Could not find vDSO base");
     }
-    Ok(AuxVecValues {vdso_base: ptr, page_size: pagesize})
-}
+    if pagesize == 0 {
+        panic!("Could not find page size");
+    }
+    AuxVecValues {vdso_base: ptr, page_size: pagesize}
+};