Date: Wed, 16 Oct 2019 16:19:52 -0700 From: Doug Hardie <bc979@lafn.org> To: MJ <mafsys1234@gmail.com> Cc: Doug Hardie <bc979@lafn.org>, FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: Extension to previous posts: Problems with ld, libc, and "struct stat" Message-ID: <FD1D1CB6-3B4F-4298-B100-DEDC4A368C67@mail.sermon-archive.info> In-Reply-To: <ccb4b6bc-df7e-eab5-bf41-085f979ad53e@gmail.com> References: <E92C7F26-912F-4443-A37B-E7AF9E025CD8@mail.sermon-archive.info> <ccb4b6bc-df7e-eab5-bf41-085f979ad53e@gmail.com>
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> On 16 October 2019, at 16:09, MJ <mafsys1234@gmail.com> wrote:
>=20
>=20
> On 17/10/2019 8:02 am, Doug Hardie wrote:
>> Here is an issue that has plagued me for some time:
>>=20
>> testlib.c:
>> #include <sys/stat.h>
>> #include <stdio.h>
>> #include <string.h>
>> #include <strings.h>
>>=20
>> char id[4];
>> int sock;
>>=20
>> 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);
>> }
>>=20
>>=20
>> testprog.c:
>> #include <stdio.h>
>>=20
>> extern char id[4];
>> extern int sock;
>>=20
>> void testfunc(void);
>> int main(int argc, char **argv) {
>> testfunc();
>> printf ("id =3D %s\n", id);
>> printf ("sock =3D %d\n", sock);
>> return 0;
>> }
>>=20
>>=20
>> Makefile:
>> all: clean testprog run
>>=20
>> 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
>>=20
>> clean:
>> rm -f testlib.o testlib.so testprog
>>=20
>> run:
>> ./testprog
>>=20
>>=20
>> 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
>>=20
>>=20
>> 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
>>=20
>>=20
>> 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?
>>=20
>> 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.
>>=20
>> -- Doug
>=20
> Well it's obviously wrong. It's a bug in lldb. Unless you have to =
specifically load the shared library in? (process load testlib?)
>=20
> I tested this with gdb, it works as expected. That's probably why I =
still use gdb...
>=20
I tried gdb on 12.0 and got the following:
master# /usr/libexec/gdb testprog
GNU gdb 6.1.1 [FreeBSD]
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you =
are
welcome to change it and/or distribute copies of it under certain =
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for =
details.
This GDB was configured as "amd64-marcel-freebsd"...
(gdb) b main
Breakpoint 1 at 0x201366: file testprog.c, line 8.
(gdb) r
Starting program: /usr/home/doug/zzz/testprog=20
Breakpoint 1, main (argc=3D1, argv=3D0x7fffffffeb30) at testprog.c:8
8 testfunc();
Current language: auto; currently minimal
(gdb) n
Size of testlib.c is 268 bytes.
9 printf ("id =3D %s\n", id);
(gdb) p id
$1 =3D 0x80024b000 ""
(gdb) p sock
$2 =3D 0
(gdb) n
id =3D aa
10 printf ("sock =3D %d\n", sock);
(gdb)=20
sock =3D 5
11 return 0;
(gdb) ^DThe program is running. Exit anyway? (y or n) y
It doesn't throw an error, but it shows incorrect values.
-- Doug
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