https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88727
Bug ID: 88727
Summary: Diagnostics improvement: Detection of undefined
behaviour. Incomplete type in tenative definition with
internal linkage.
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: anders.granlund.0 at gmail dot com
Target Milestone: ---
Test case (prog.c):
static struct S s;
int main()
{
}
struct S { int x; };
Compilation command line:
gcc prog.c -Wall -Wextra -std=c11 -pedantic-errors
Observed behaviour:
No error messages outputes.
Possible improvement of behaviour:
Outputing an error message about using an incomplete type in the tenative
definition static struct S s; .
The program has undefined behaviour becuase of a violation of 6.9.2/2:
"If the declaration of an identifier for an object is a tentative definition
and has internal linkage, the declared type shall not be an incomplete
type."
GCC detects such undefined behaviour in other cases (for example using the
incomplete type int []). It would be good if it could also hande the case in
the test case for this bug report.
Note:
Clang detects the undefined behaviour for this program and outputs an error
message.
