Improve error messages of auxv loading

Author: Kobzol

library/std_detect/src/detect/os/linux/auxvec.rs

@@ -118,7 +118,7 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
     {
         // If calling getauxval fails, try to read the auxiliary vector from
         // its file:
-        auxv_from_file("/proc/self/auxv")
+        auxv_from_file("/proc/self/auxv").map_err(|_| ())
     }
     #[cfg(not(feature = "std_detect_file_io"))]
     {
@@ -156,17 +156,22 @@ fn getauxval(key: usize) -> Result<usize, ()> {
 /// Tries to read the auxiliary vector from the `file`. If this fails, this
 /// function returns `Err`.
 #[cfg(feature = "std_detect_file_io")]
-pub(super) fn auxv_from_file(file: &str) -> Result<AuxVec, ()> {
+pub(super) fn auxv_from_file(file: &str) -> Result<AuxVec, alloc::string::String> {
     let file = super::read_file(file)?;
+    auxv_from_file_bytes(&file)
+}
 
+/// Read auxiliary vector from a slice of bytes.
+#[cfg(feature = "std_detect_file_io")]
+pub(super) fn auxv_from_file_bytes(bytes: &[u8]) -> Result<AuxVec, alloc::string::String> {
     // See <https://github.com/torvalds/linux/blob/v5.15/include/uapi/linux/auxvec.h>.
     //
     // The auxiliary vector contains at most 34 (key,value) fields: from
     // `AT_MINSIGSTKSZ` to `AT_NULL`, but its number may increase.
-    let len = file.len();
+    let len = bytes.len();
     let mut buf = alloc::vec![0_usize; 1 + len / core::mem::size_of::<usize>()];
     unsafe {
-        core::ptr::copy_nonoverlapping(file.as_ptr(), buf.as_mut_ptr() as *mut u8, len);
+        core::ptr::copy_nonoverlapping(bytes.as_ptr(), buf.as_mut_ptr() as *mut u8, len);
     }
 
     auxv_from_buf(&buf)
@@ -175,7 +180,7 @@ pub(super) fn auxv_from_file(file: &str) -> Result<AuxVec, ()> {
 /// Tries to interpret the `buffer` as an auxiliary vector. If that fails, this
 /// function returns `Err`.
 #[cfg(feature = "std_detect_file_io")]
-fn auxv_from_buf(buf: &[usize]) -> Result<AuxVec, ()> {
+fn auxv_from_buf(buf: &[usize]) -> Result<AuxVec, alloc::string::String> {
     // Targets with only AT_HWCAP:
     #[cfg(any(
         target_arch = "riscv32",
@@ -220,7 +225,7 @@ fn auxv_from_buf(buf: &[usize]) -> Result<AuxVec, ()> {
     }
     // Suppress unused variable
     let _ = buf;
-    Err(())
+    Err(alloc::string::String::from("hwcap not found"))
 }
 
 #[cfg(test)]

library/std_detect/src/detect/os/linux/mod.rs

@@ -6,14 +6,16 @@ use alloc::vec::Vec;
 mod auxvec;
 
 #[cfg(feature = "std_detect_file_io")]
-fn read_file(path: &str) -> Result<Vec<u8>, ()> {
-    let mut path = Vec::from(path.as_bytes());
+fn read_file(orig_path: &str) -> Result<Vec<u8>, alloc::string::String> {
+    use alloc::format;
+
+    let mut path = Vec::from(orig_path.as_bytes());
     path.push(0);
 
     unsafe {
         let file = libc::open(path.as_ptr() as *const libc::c_char, libc::O_RDONLY);
         if file == -1 {
-            return Err(());
+            return Err(format!("Cannot open file at {orig_path}: {}", *libc::__errno_location()));
         }
 
         let mut data = Vec::new();
@@ -23,7 +25,10 @@ fn read_file(path: &str) -> Result<Vec<u8>, ()> {
             match libc::read(file, spare.as_mut_ptr() as *mut _, spare.len()) {
                 -1 => {
                     libc::close(file);
-                    return Err(());
+                    return Err(format!(
+                        "Error while reading from file at {orig_path}: {}",
+                        *libc::__errno_location()
+                    ));
                 }
                 0 => break,
                 n => data.set_len(data.len() + n as usize),