GDB Dis-Flavor set to Intel, but showing AT&T-style - c++

Question

I've set the disassembly-flavor of the gdb-debugger to Intel (both: su & normal user), but anyway it's still showing the assembly-code in AT&T notation:
patrick#localhost:~/Dokumente/Projekte$ gdb -q ./a.out
Reading symbols from ./a.out...done.
(gdb) break main
Breakpoint 1 at 0x40050e: file firstprog.c, line 5.
(gdb) run
Starting program: /home/patrick/Dokumente/Projekte/a.out
Breakpoint 1, main () at firstprog.c:5
5 for(i=0; i < 10; i++)
(gdb) show disassembly
The disassembly flavor is "intel".
(gdb) info registers
rax 0x400506 4195590
rbx 0x0 0
rcx 0x0 0
rdx 0x7fffffffe2d8 140737488347864
rsi 0x7fffffffe2c8 140737488347848
rdi 0x1 1
rbp 0x7fffffffe1e0 0x7fffffffe1e0
(gdb) info register eip
Invalid register `eip'
I did restart the computer. My OS is Kali Linux amd64.
I have the following questions:
Why is gdb still showing the AT&T notation?
Why is the register EIP (instruction pointer) shown as invalid register?

Answer 1

You are misunderstanding what disassembly flavour means. It means exactly that: what the disassembly looks like when you view machine code in a human-readable(ish) form.
To print registers (or use registers in any other context), you need to use $reg, such as $rip or $pc, $eax, etc.
If I disassemble one of my programs with at&t syntax, gdb shows this:
0x00000000007378f0 <+0>: push %rbp
0x00000000007378f1 <+1>: mov %rsp,%rbp
0x00000000007378f4 <+4>: sub $0x20,%rsp
0x00000000007378f8 <+8>: movl $0x0,-0x4(%rbp)
0x00000000007378ff <+15>: mov %edi,-0x8(%rbp)
0x0000000000737902 <+18>: mov %rsi,-0x10(%rbp)
=> 0x0000000000737906 <+22>: mov -0x10(%rbp),%rsi
0x000000000073790a <+26>: mov (%rsi),%rdi
0x000000000073790d <+29>: callq 0x737950 <FindLibPath(char const*)>
0x0000000000737912 <+34>: xor %eax,%eax
Then do this:
(gdb) set disassembly-flavor intel
(gdb) disass main
Dump of assembler code for function main(int, char**):
0x00000000007378f0 <+0>: push rbp
0x00000000007378f1 <+1>: mov rbp,rsp
0x00000000007378f4 <+4>: sub rsp,0x20
0x00000000007378f8 <+8>: mov DWORD PTR [rbp-0x4],0x0
0x00000000007378ff <+15>: mov DWORD PTR [rbp-0x8],edi
0x0000000000737902 <+18>: mov QWORD PTR [rbp-0x10],rsi
=> 0x0000000000737906 <+22>: mov rsi,QWORD PTR [rbp-0x10]
0x000000000073790a <+26>: mov rdi,QWORD PTR [rsi]
0x000000000073790d <+29>: call 0x737950 <FindLibPath(char const*)>
0x0000000000737912 <+34>: xor eax,eax
and you can see the difference. But the names of registers and how you use registers on the gdb command-line isn't changing, you need a $reg in both cases.