From 6f96674cc0ce9c148d864fa69550e7c44d68d188 Mon Sep 17 00:00:00 2001
From: Michael Tautschnig <tautschn@amazon.com>
Date: Tue, 28 Jun 2022 09:14:37 +0000
Subject: [PATCH] C entry point generator: no unconditional conversion to
 pointer type

Do not try to create a pointer_typet when the type might not actually be
a pointer type. This was triggerable by syntactically well-formed C
input and should instead be handled by a user-facing error message.

Fixes: #6975
---
 regression/ansi-c/main1/main.c    |  4 ++++
 regression/ansi-c/main1/test.desc | 11 +++++++++++
 src/ansi-c/ansi_c_entry_point.cpp | 11 ++++++++++-
 3 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 regression/ansi-c/main1/main.c
 create mode 100644 regression/ansi-c/main1/test.desc

diff --git a/regression/ansi-c/main1/main.c b/regression/ansi-c/main1/main.c
new file mode 100644
index 00000000000..1b685efc386
--- /dev/null
+++ b/regression/ansi-c/main1/main.c
@@ -0,0 +1,4 @@
+int main(char *argv, int arc)
+{
+  return 0;
+}
diff --git a/regression/ansi-c/main1/test.desc b/regression/ansi-c/main1/test.desc
new file mode 100644
index 00000000000..a381531029f
--- /dev/null
+++ b/regression/ansi-c/main1/test.desc
@@ -0,0 +1,11 @@
+CORE test-c++-front-end
+main.c
+
+'main' with signature 'signed int \(char \*argv, signed int arc\)' found
+^EXIT=(64|1)$
+^SIGNAL=0$
+--
+Invariant check failed
+--
+This test is to ensure that non-standard C entry points are handled gracefully
+and with a message to the user.
diff --git a/src/ansi-c/ansi_c_entry_point.cpp b/src/ansi-c/ansi_c_entry_point.cpp
index 62afc6c2ca5..9e1fd973bec 100644
--- a/src/ansi-c/ansi_c_entry_point.cpp
+++ b/src/ansi-c/ansi_c_entry_point.cpp
@@ -248,7 +248,16 @@ bool generate_ansi_c_start_function(
     {
       // ok
     }
-    else if(parameters.size()==2 || parameters.size()==3)
+    // The C standard (and any related architecture descriptions) enforces an
+    // order of parameters. The user, however, may supply arbitrary
+    // (syntactically valid) C code, even one that does not respect the calling
+    // conventions set out in the C standard. If the user does supply such code,
+    // then we can only tell them that they got it wrong, which is what we do
+    // via the error message in the else branch of this code.
+    else if(
+      parameters.size() >= 2 && parameters[1].type().id() == ID_pointer &&
+      (parameters.size() == 2 ||
+       (parameters.size() == 3 && parameters[2].type().id() == ID_pointer)))
     {
       namespacet ns(symbol_table);