[Bug debug/84550] [8 Regression] stepping through gcc does not work with gdb 8.0.1

[palves at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84550

--- Comment #6 from Pedro Alves <palves at redhat dot com> ---
I see the same thing with your reduced testcase:

~~~
infrun: TARGET_WAITKIND_STOPPED
infrun: stop_pc = 0x400580
infrun: stepped into subroutine
infrun: inserting step-resume breakpoint at 0x400410
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread
[process 13966] at 0x400580
~~~

0x400410 is never hit.

With:

(gdb) disassemble /s qux
Dump of assembler code for function qux(C*):
t.c:
33        if (!p->c) __builtin_abort ();
   0x0000000000400410 <+0>:     callq  0x400400 <abort@plt>
   0x0000000000400415:  nopw   %cs:0x0(%rax,%rax,1)
   0x000000000040041f:  nop
...
   0x0000000000400578 <+16>:    nopl   0x0(%rax,%rax,1)

9         return false;
   0x0000000000400580 <+0>:     xor    %eax,%eax
   0x0000000000400582 <+2>:     retq   
   0x0000000000400583:  nopl   (%rax)
   0x0000000000400586:  nopw   %cs:0x0(%rax,%rax,1)
---Type <return> to continue, or q <return> to quit---

... we see that "foo" is sharing the tail end of qux?

And we see that "0x400410", where GDB things foo's prologue ends,
is actually the end of qux's prologue:

(gdb) disassemble /s foo
Dump of assembler code for function qux(C*):
t.c:
33        if (!p->c) __builtin_abort ();
   0x0000000000400410 <+0>:     callq  0x400400 <abort@plt>
   0x0000000000400415:  nopw   %cs:0x0(%rax,%rax,1)
   0x000000000040041f:  nop

When we do "b foo", gdb sets a breakpoint at 0x400580 instead (passed foo's
prologue).  I don't know why it gets it wrong when stepping into the function.