gdb step into function in executable compiled with -r now

[Manfred <mx2927 at gmail dot com>]

Hi all,

I would like some explanation about the following behaviour, that I 
can't understand from the documentation:

Using gcc and gdb, I am experiencing that with an executable linked with 
-r now I can't step into functions defined in shared libraries.
Just removing -r now from the linker options allows gdb to step in as 
expected
Here is some sample code (gcc 7.2.1 and gdb 8.0.1 on x86_64):

// lib/foo.h
void foo(int);

// main.c
#include <stdio.h>
#include "lib/foo.h"

int main()
{
  const int arg = 13;
  printf("calling foo(%d)...\n", arg);
  foo(arg);
  puts("back into main()");
}

// lib/foo.c
#include <stdio.h>
#include "foo.h"

void foo(int val)
{
  printf("running foo(%d)\n", val);
}

building the above with -r now:

$ make
cc -g -Wall -fPIC   -c -o main.o main.c
make -C ./lib
make[1]: Entering directory './lib'
cc -g -Wall -fPIC   -c -o foo.o foo.c
gcc -shared -o libfoo.so foo.o -Wl,-h,libfoo.so.0 -Wl,-z,relro,-z,now 
-Wl,--export-dynamic -Wl,--as-needed -fstack-protector -Wl,-rpath,`pwd` 
-Wl,-Bdynamic
ln -s libfoo.so libfoo.so.0
make[1]: Leaving directory './lib'
gcc -o foo main.o -pie -Wl,-z,relro -Wl,-z,now -lpthread 
-Wl,-no-undefined -Wl,--export-dynamic -Wl,--as-needed -fstack-protector 
-Wl,-rpath,`pwd`/lib -L`pwd`/lib -Wl,-Bdynamic -lfoo

and gdb:

$ gdb foo
GNU gdb (GDB) Fedora 8.0.1-26.fc26
Copyright (C) 2017 Free Software Foundation, Inc.
.....
Reading symbols from foo...done.
(gdb) b main
Breakpoint 1 at 0x8c2: file main.c, line 7.
(gdb) run
Starting program: ./foo
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 1, main () at main.c:7
7	  const int arg = 13;
(gdb) next
8	  printf("calling foo(%d)...\n", arg);
(gdb)
calling foo(13)...
9	  foo(arg);
(gdb) step                            <== this doesn't work
running foo(13)
10	  puts("back into main()");
(gdb) cont
Continuing.
back into main()
[Inferior 1 (process 7113) exited normally]
(gdb)

linking the executable without -r now:

$ make
cc -g -Wall -fPIC   -c -o main.o main.c
make -C ./lib
make[1]: Entering directory './lib'
cc -g -Wall -fPIC   -c -o foo.o foo.c
gcc -shared -o libfoo.so foo.o -Wl,-h,libfoo.so.0 -Wl,-z,relro,-z,now 
-Wl,--export-dynamic -Wl,--as-needed -fstack-protector -Wl,-rpath,`pwd` 
-Wl,-Bdynamic
ln -s libfoo.so libfoo.so.0
make[1]: Leaving directory './lib'
*** -r now *removed* in the following ***
gcc -o foo main.o -pie -Wl,-z,relro  -lpthread -Wl,-no-undefined 
-Wl,--export-dynamic -Wl,--as-needed -fstack-protector 
-Wl,-rpath,`pwd`/lib -L`pwd`/lib -Wl,-Bdynamic -lfoo

and gdb:

$ gdb foo
GNU gdb (GDB) Fedora 8.0.1-26.fc26
......
Reading symbols from foo...done.
(gdb) b main
Breakpoint 1 at 0x8e2: file main.c, line 7.
(gdb) run
Starting program: ./foo
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 1, main () at main.c:7
7	  const int arg = 13;
(gdb) next
8	  printf("calling foo(%d)...\n", arg);
(gdb)
calling foo(13)...
9	  foo(arg);
(gdb) step                            <== this does work now
foo (val=13) at foo.c:7
7	  printf("running foo(%d)\n", val);
(gdb) cont
Continuing.
running foo(13)
back into main()
[Inferior 1 (process 7200) exited normally]
(gdb)

stepi does step into, but it is less friendly.

Thanks in advance,
Manfred