http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55937
Bug #: 55937
Summary: lto hides possible link issues
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: lto
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: bo...@fau.re
When compiling the following on linux where gethrtime is not defined, it links
with -O1 but not with -O0:
char gethrtime ();
char (*f) () = gethrtime;
int main () {
return f != gethrtime;
}
'gcc-4.7.2 -O1 -flto -o conftest conftest.c' works, while 'gcc-4.7.2 -O0 -flto
-o conftest conftest.c' outputs:
/tmp/ccT5O10r.ltrans0.ltrans.o: In function `main':
ccT5O10r.ltrans0.o:(.text+0xd): undefined reference to `gethrtime'
/tmp/ccT5O10r.ltrans0.ltrans.o:(.data+0x0): undefined reference to `gethrtime'
collect2: error: ld returned 1 exit status
Compiling with -fwhole-program, it would fail as expected:
'gcc-4.7.2 -O1 -fwhole-program -o conftest conftest.c' outputs:
/tmp/ccaHfhb0.o:(.rodata+0x0): undefined reference to `gethrtime'
collect2: error: ld returned 1 exit status
That code is actually produced by the following autoconf macro while
configuring erlang-R15B02:
AC_CHECK_FUNC(gethrtime)
The macro would include <limits.h> but since it's not defined, the same
behaviour is shown without that include.
