Make sure that the fortified function conditionals are constant

In _FORTIFY_SOURCE=3, the size expression may be non-constant,
resulting in branches in the inline functions remaining intact and
causing a tiny overhead.  Clang (and in future, gcc) make sure that
the -1 case is always safe, i.e. any comparison of the generated
expression with (size_t)-1 is always false so that bit is taken care
of.  The rest is avoidable since we want the _chk variant whenever we
have a size expression and it's not -1.

Rework the conditionals in a uniform way to clearly indicate two
conditions at compile time:

- Either the size is unknown (-1) or we know at compile time that the
  operation length is less than the object size.  We can call the
  original function in this case.  It could be that either the length,
  object size or both are non-constant, but the compiler, through
  range analysis, is able to fold the *comparison* to a constant.

- The size and length are known and the compiler can see at compile
  time that operation length > object size.  This is valid grounds for
  a warning at compile time, followed by emitting the _chk variant.

For everything else, emit the _chk variant.

This simplifies most of the fortified function implementations and at
the same time, ensures that only one call from _chk or the regular
function is emitted.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

1 files changed, 13 insertions, 21 deletions

diff --git a/socket/bits/socket2.h b/socket/bits/socket2.h
index 9c8ac69..b28cde5 100644
--- a/socket/bits/socket2.h
+++ b/socket/bits/socket2.h
@@ -33,17 +33,12 @@ extern ssize_t __REDIRECT (__recv_chk_warn,
 __fortify_function ssize_t
 recv (int __fd, void *__buf, size_t __n, int __flags)
 {
-  if (__glibc_objsize0 (__buf) != (size_t) -1)
-    {
-      if (!__builtin_constant_p (__n))
-	return __recv_chk (__fd, __buf, __n, __glibc_objsize0 (__buf),
-			   __flags);
-
-      if (__n > __glibc_objsize0 (__buf))
-	return __recv_chk_warn (__fd, __buf, __n, __glibc_objsize0 (__buf),
-				__flags);
-    }
-  return __recv_alias (__fd, __buf, __n, __flags);
+  size_t sz = __glibc_objsize0 (__buf);
+  if (__glibc_safe_or_unknown_len (__n, sizeof (char), sz))
+    return __recv_alias (__fd, __buf, __n, __flags);
+  if (__glibc_unsafe_len (__n, sizeof (char), sz))
+    return __recv_chk_warn (__fd, __buf, __n, sz, __flags);
+  return __recv_chk (__fd, __buf, __n, sz, __flags);
 }
 
 extern ssize_t __recvfrom_chk (int __fd, void *__restrict __buf, size_t __n,
@@ -66,14 +61,11 @@ __fortify_function ssize_t
 recvfrom (int __fd, void *__restrict __buf, size_t __n, int __flags,
 	  __SOCKADDR_ARG __addr, socklen_t *__restrict __addr_len)
 {
-  if (__glibc_objsize0 (__buf) != (size_t) -1)
-    {
-      if (!__builtin_constant_p (__n))
-	return __recvfrom_chk (__fd, __buf, __n, __glibc_objsize0 (__buf),
-			       __flags, __addr, __addr_len);
-      if (__n > __glibc_objsize0 (__buf))
-	return __recvfrom_chk_warn (__fd, __buf, __n, __glibc_objsize0 (__buf),
-				    __flags, __addr, __addr_len);
-    }
-  return __recvfrom_alias (__fd, __buf, __n, __flags, __addr, __addr_len);
+  size_t sz = __glibc_objsize0 (__buf);
+  if (__glibc_safe_or_unknown_len (__n, sizeof (char), sz))
+    return __recvfrom_alias (__fd, __buf, __n, __flags, __addr, __addr_len);
+  if (__glibc_unsafe_len (__n, sizeof (char), sz))
+    return __recvfrom_chk_warn (__fd, __buf, __n, sz, __flags, __addr,
+				__addr_len);
+  return __recvfrom_chk (__fd, __buf, __n, sz, __flags, __addr, __addr_len);
 }