Re: [PATCH] Detect escape of ErrorContextCallback stack pointers (and from PG_TRY() )

Craig Ringer <craig(at)2ndquadrant(dot)com> writes:
> Example here:
> https://github.com/ringerc/scrapcode/tree/master/c/clang_return_stack_checks
> So I find that actually, the __attribute__((callback(fn)) approach is
> unnecessary for the purpose proposed.

I tested this by injecting some faults of the described sort.

diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index db7d24a511..eaf7716816 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -3025,6 +3025,8 @@ CopyFrom(CopyState cstate)

myslot = CopyMultiInsertInfoNextFreeSlot(&multiInsertInfo,
resultRelInfo);
+ if (!myslot)
+ return 0;
}

/*

leads to

/home/tgl/pgsql/src/backend/commands/copy.c:3029:6: warning: Address of stack memory associated with local variable 'errcallback' is still referred to by the global variable 'error_context_stack' upon returning to the caller. This will be a dangling reference
return 0;
^~~~~~~~

So that's good. However, a similar experiment with returning from inside
a PG_TRY does *not* produce a warning. I suspect maybe the compiler
throws up its hands when it sees sigsetjmp?

(These results from clang 10.0.0 on Fedora 32.)

regards, tom lane