Date: Tue, 15 Oct 2019 20:44:00 +0200 From: Jan Behrens <jbe-mlist@magnetkern.de> To: freebsd-questions@freebsd.org Subject: Problems with ld, libc, and "struct stat" Message-ID: <20191015204400.e33c8f62af711e829288ddae@magnetkern.de>
next in thread | raw e-mail | index | archive | help
Hello,
I stumbled across a weird problem related stat() that (according to my
research) seems to be related to an update of the "struct stat"
C-structure in recent Kernel versions.
Consider the following two files.
testlib.c:
#include <sys/stat.h>
#include <stdio.h>
void testfunc() {
struct stat sb;
stat("testlib.c", &sb);
printf("Size of testlib.c is %i bytes.\n", (int)sb.st_size);
}
testprog.c:
extern void testfunc(void);
int main(int argc, char **argv) {
testfunc();
return 0;
}
Now I run:
% cc -Wall -c -fPIC -o testlib.o testlib.c
% cc -Wall -o testprog testlib.o testprog.c
% ./testprog
Size of testlib.c is 168 bytes.
But when I make a shared library like this, I get a different result:
% ld -shared -o testlib.so testlib.o
% cc -Wall -o testprog `pwd`/testlib.so testprog.c
% ./testprog
Size of testlib.c is 394655000 bytes.
This result is obviously wrong. Note that I did not get any compiler or
linker warnings or errors; yet there happens a bad error during runtime!
With several attempts of trial and error, I figured out that the
problem does not appear when appending "-L/usr/lib -lc" to the ld call
when linking the shared library:
% ld -shared -o testlib.so testlib.o -L/usr/lib -lc
% cc -Wall -o testprog `pwd`/testlib.so testprog.c
% ./testprog
Size of testlib.c is 168 bytes.
Can anyone tell me why is that and if I am supposed to always add
"-L/usr/lib -lc" when creating an *.so file?
Is this maybe a bug in FreeBSD or ld? Or am I using the linker in a
wrong way?
Kind regards,
Jan Behrens
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20191015204400.e33c8f62af711e829288ddae>