Date: Wed, 16 Oct 2019 14:02:24 -0700 From: Doug Hardie <bc979@lafn.org> To: FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Extension to previous posts: Problems with ld, libc, and "struct stat" Message-ID: <E92C7F26-912F-4443-A37B-E7AF9E025CD8@mail.sermon-archive.info>
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Here is an issue that has plagued me for some time:
testlib.c:
#include <sys/stat.h>
#include <stdio.h>
#include <string.h>
#include <strings.h>
char id[4];
int sock;
void testfunc() {
struct stat sb;
stat("testlib.c", &sb);
strcpy (id, "aa");
sock =3D 5;
printf("Size of testlib.c is %i bytes.\n", (int)sb.st_size);
}
testprog.c:
#include <stdio.h>
extern char id[4];
extern int sock;
void testfunc(void);
int main(int argc, char **argv) {
testfunc();
printf ("id =3D %s\n", id);
printf ("sock =3D %d\n", sock);
return 0;
}
Makefile:
all: clean testprog run
testprog:
cc -Wall -g -c -fPIC -o testlib.o testlib.c
cc -shared -Wl,-export-dynamic -o testlib.so testlib.o
cc -Wall -g -o testprog ./testlib.so testprog.c
clean:
rm -f testlib.o testlib.so testprog
run:
./testprog
Using make:
rm -f testlib.o testlib.so testprog
cc -Wall -g -c -fPIC -o testlib.o testlib.c
cc -shared -Wl,-export-dynamic -o testlib.so testlib.o
cc -Wall -g -o testprog ./testlib.so testprog.c
./testprog
Size of testlib.c is 268 bytes.
id =3D aa
sock =3D 5
Running lldb:
master# lldb testprog
(lldb) target create "testprog"
Current executable set to 'testprog' (x86_64).
(lldb) b main
Breakpoint 1: where =3D testprog`main + 22 at testprog.c:8, address =3D =
0x0000000000201366
(lldb) r
Process 34787 launching
Process 34787 launched: '/home/doug/zzz/testprog' (x86_64)
Process 34787 stopped
* thread #1, name =3D 'testprog', stop reason =3D breakpoint 1.1
frame #0: 0x0000000000201366 testprog`main(argc=3D1, =
argv=3D0x00007fffffffeb38) at testprog.c:8
5 =09
6 void testfunc(void);
7 int main(int argc, char **argv) {
-> 8 testfunc();
9 printf ("id =3D %s\n", id);
10 printf ("sock =3D %d\n", sock);
11 return 0;
(lldb) n
Size of testlib.c is 268 bytes.
Process 34787 stopped
* thread #1, name =3D 'testprog', stop reason =3D step over
frame #0: 0x000000000020137f testprog`main(argc=3D1, =
argv=3D0x00007fffffffeb38) at testprog.c:9
6 void testfunc(void);
7 int main(int argc, char **argv) {
8 testfunc();
-> 9 printf ("id =3D %s\n", id);
10 printf ("sock =3D %d\n", sock);
11 return 0;
12 }
(lldb) p id
error: use of undeclared identifier 'id'
(lldb) p sock
error: Couldn't materialize: couldn't get the value of variable sock: =
testlib.so[0x4004] can't be resolved, testlib.so is not currently loaded
error: errored out in DoExecute, couldn't PrepareToExecuteJITExpression
(lldb) c
id =3D aa
sock =3D 5
Process 34787 resuming
You notice that lldb cannot display values for id or sock. It even =
gives quite different messages about them. However the program can =
access the values and it prints them out properly. Why can't lldb see =
them? How can that be corrected?
What is even more interesting is that in the real application there are =
quite a few of these global variables and lldb can display some of them, =
just not all. Possibly it has to do with the specific names as DATE =
generally works. sock and id never seem to work.
-- Doug
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