Re: [PATCH] Fix target architecture address size inside gdbarch structure

[Simon Marchi <simon.marchi@polymtl.ca>]

On 2018-10-17 07:33, Denis Dmitriev wrote:
> hi!
> 
> gcc --version
> gcc (Ubuntu 5.4.0-6ubuntu1~16.04.10) 5.4.0 20160609
> Copyright (C) 2015 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.  There is 
> NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR 
> PURPOSE.
> 
> uname -a
> Linux heroboecPC 4.15.0-34-generic #37~16.04.1-Ubuntu SMP Tue Aug 28
> 10:44:06 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
> 
> 
> I took gdb 8.2.50.20180906-git (hash:
> 739ab2e92e1840c9285f3cfce1f1236c0fa68730).
> ./configure --host=x86_64-linux --target=mips64-linux-uclibc
> make
> After that, I start the debugger, install the architecture for 
> debugging.
> set arch mips:octeon2
> tar rem :1234 (i have qemu with mips to connect)
> disas $pc, $pc+20
> 0xbfc00000 in ?? ()
> (gdb) disas $pc, $pc+20
> Dump of assembler code from 0xbfc00000 to 0xbfc00014:
> => 0xbfc00000:  Cannot access memory at address 0xbfc00000
> 
> Address size is 32 bit instead of 64.

Looking at the code, there is the mips ABI setting that comes into play, 
that's where the ptr size (and consequently the addr size):

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gdb/mips-tdep.c;h=bf44c52f5d2ad73605cdfaabe1ac1d2bde822ef9;hb=HEAD#l8541

When loading a binary in GDB, it auto detects the ABI:

$ ./gdb -q --data-directory=data-directory test
Reading symbols from test...
(No debugging symbols found in test)
(gdb) show architecture
The target architecture is set automatically (currently mips:isa64r2)
(gdb) show mips abi
The MIPS ABI is set automatically (currently "n64").


If you don't provide a binary to gdb, then you should probably set this 
to the right value:

(gdb) set architecture mips:octeon2
The target architecture is assumed to be mips:octeon2
(gdb) show mips abi
The MIPS ABI is set automatically (currently "o32").
(gdb) p sizeof(void*)
$1 = 4
(gdb) set mips abi n64
(gdb) p sizeof(void*)
$2 = 8

I don't know if it makes sense to have the architecture "mips:octeon2" 
along with a 32-bits ABI, I don't really know much about MIPS.  If it 
doesn't, perhaps it would be possible to select a more sensible ABI by 
default when selecting that architecture.  But for now, you have to 
select it by hand.  Or if you can provide the binary to gdb, that's the 
ideal.

Simon