On Sat, Oct 05, 2019 at 07:47:50PM +0200, Christoph Zwerschke wrote:
>
> Am 05.10.2019 um 18:47 schrieb Justin Pryzby:
> > On Sat, Oct 05, 2019 at 06:37:36PM +0200, Christoph Zwerschke wrote:
> >> Are you sure you compiled that with the pgconfig.h of Postgres 12?
> >> setup.py is using the includes specified by the pgconfig tool.
> > The intended behavior is to hit the runtime version check and then
> > return None.
> > To check, I compiled against pg12 and then downgraded libpq to v10.
> > Built like: PATH=/usr/lib/postgresql/12/bin:$PATH ./setup.py build
> > If I hadn't, then it wouldn't have referenced PQresultMemorySize at
> > all, right ?
>
> Ah, yes, you're right. The runtime checks are useless because you can't even
> load a shared library that doesn't support all the symbols that you are
> referencing somewhere.
In general, that's false, due to lazy binding (man ld.so: /LD_BIND_NOW/)
...but maybe true for python's c modules ??
$ sudo dpkg -i /var/cache/apt/archives/libpq{5,-dev}_12*deb
$ make CFLAGS="-Wall -Wextra -O3 -g -I /usr/include/postgresql" LDLIBS=-lpq t
$ PGDATABASE=postgres ./t 1
3459288
$ PGDATABASE=postgres ./t 1
./t: symbol lookup error: ./t: undefined symbol: PQresultMemorySize
$ PGDATABASE=postgres ./t 0 && echo OK
OK
$ LD_BIND_NOW=t PGDATABASE=postgres ./t 0
./t: symbol lookup error: ./t: undefined symbol: PQresultMemorySize
Justin
// make CFLAGS="-Wall -Wextra -O3 -g -I /usr/include/postgresql" LDLIBS=-lpq t
#include <libpq-fe.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char **argv)
{
PGconn *conn = PQconnectdb(""); // PGDATABASE dbname=postgres");
if (PQstatus(conn) != CONNECTION_OK)
exit(1);
PGresult *res = PQexec(conn, "SELECT generate_series(1,99999)");
if (argv[1][0] == '1')
printf("%zd\n", PQresultMemorySize(res));
return 0;
}
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