fesvr: replace use of `std::vector::operator[0]`

This replaces multiple uses of `std::vector::operator[]` where the
parameter is a constant `0` with the use of C++11's `std::vector::data`
method.  This fixes the root cause of invalid memory accesses.
`std::vector::operator[]` is an unchecked memory access, and when the
buffers are zero-sized (that is the buffer container is empty) either
due to a 0 padding in the case of elfloader or NULL parameters to
syscalls where permitted, the unchecked access may cause an invalid
memory access.  The use of `std::vector::data` is permitted even in such
a case, though the returned memory may not be dereferenced.  The general
usage of the returned pointer is to pass to `memif_t`, which is careful
about 0-sized buffer accesses, and so passing the result of
`std::vector::data` is safe.  This is theoretically a better access
pattern as it also avoids having the compiler to re-materialize the
pointer from the de-referenced location.

1 files changed, 1 insertions, 1 deletions

diff --git a/fesvr/htif.cc b/fesvr/htif.cc
index 1a9d0fc..234032b 100644
--- a/fesvr/htif.cc
+++ b/fesvr/htif.cc
@@ -169,7 +169,7 @@ void htif_t::stop()
   if (!sig_file.empty() && sig_len) // print final torture test signature
   {
     std::vector<uint8_t> buf(sig_len);
-    mem.read(sig_addr, sig_len, &buf[0]);
+    mem.read(sig_addr, sig_len, buf.data());
 
     std::ofstream sigs(sig_file);
     assert(sigs && "can't open signature file!");