Re: [PATCH 2/5] Change linetables to be objfile-independent

[Simon Marchi <simark@simark.ca>]

On 3/16/23 10:02, Tom Tromey wrote:
>>>>>> "Simon" == Simon Marchi via Gdb-patches <gdb-patches@sourceware.org> writes:
> 
> Simon> Looks like we're trying to read from the inferior at an unrelocated
> Simon> address.  From some previous bug, I recall that you were using a system
> Simon> with no-PIE as a default, so that could be why you don't see it.
> 
> I tried building this executable with -fPIE and it still seems to work
> for me :(

Ok, I'll look into it then.

I can reproduce it like hand like this:

    $ gcc -fno-stack-protector -c \
        -o /home/smarchi/build/binutils-gdb/gdb/testsuite/outputs/gdb.base/disasm-optim/disasm-optim0.o \
        /home/smarchi/src/binutils-gdb/gdb/testsuite/gdb.base/disasm-optim.S \
        -fPIE
    $ gcc /home/smarchi/build/binutils-gdb/gdb/testsuite/outputs/gdb.base/disasm-optim/disasm-optim0.o \
        -pie -o disasm-optim

    $ gdb ./gdb -nx -q --data-directory=data-directory disasm-optim
    Reading symbols from disasm-optim...
    (gdb) start

    This GDB supports auto-downloading debuginfo from the following URLs:
      <https://debuginfod.archlinux.org>
    Enable debuginfod for this session? (y or [n]) n
    Debuginfod has been disabled.
    To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
    Temporary breakpoint 1 at 0x1120: file disasm-optim.c, line 25.
    Starting program: /home/smarchi/build/binutils-gdb/gdb/disasm-optim
    [Thread debugging using libthread_db enabled]
    Using host libthread_db library "/usr/lib/../lib/libthread_db.so.1".

    Temporary breakpoint 1, main () at disasm-optim.c:25
    25      disasm-optim.c: No such file or directory.
    (gdb) disassemble main
    Dump of assembler code for function main:
    => 0x0000555555555120 <+0>:     mov    0x2ef2(%rip),%eax        # 0x555555558018 <y>
       0x0000555555555126 <+6>:     test   %eax,%eax
       0x0000555555555128 <+8>:     js     0x555555555140 <main+32>
       0x000055555555512a <+10>:    lea    0xa(%rax),%edx
       0x000055555555512d <+13>:    test   %eax,%eax
       0x000055555555512f <+15>:    mov    $0x1,%eax
       0x0000555555555134 <+20>:    cmovne %edx,%eax
       0x0000555555555137 <+23>:    mov    %eax,0x2ed7(%rip)        # 0x555555558014 <x>
       0x000055555555513d <+29>:    xor    %eax,%eax
       0x000055555555513f <+31>:    ret
       0x0000555555555140 <+32>:    add    %eax,%eax
       0x0000555555555142 <+34>:    jmp    0x555555555137 <main+23>
    End of assembler dump.
    (gdb) disassemble /s main
    Dump of assembler code for function main:
    Cannot access memory at address 0x1120

If I link with -no-pie, then it works.

Simon