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

[Denis Dmitriev <zealot351@gmail.com>]

This behavior is correct for the case when there is a specific elf file.
But I think in the case when using remote debugging and manual adjustment
of the architecture, it's possible to choose the ABI type without an elf
file.
All necessary information is already available in the structure of the
gdbarch->bfd_arch_info.


For example mips-tdep.c

8067 static struct gdbarch *
8068 mips_gdbarch_init (struct gdbarch_info info, struct gdbarch_list
*arches)
8069 {
8070   struct gdbarch *gdbarch;
8071   struct gdbarch_tdep *tdep;
8072   int elf_flags;
8073   enum mips_abi mips_abi, found_abi, wanted_abi;
8074   int i, num_regs;
8075   enum mips_fpu_type fpu_type;
8076   struct tdesc_arch_data *tdesc_data = NULL;
8077   int elf_fpu_type = Val_GNU_MIPS_ABI_FP_ANY;
8078   const char **reg_names;
8079   struct mips_regnum mips_regnum, *regnum;
8080   enum mips_isa mips_isa;
8081   int dspacc;
8082   int dspctl;
8083
8084   /* First of all, extract the elf_flags, if available.  */
8085   if (info.abfd && bfd_get_flavour (info.abfd) ==
bfd_target_elf_flavour)
8086     elf_flags = elf_elfheader (info.abfd)->e_flags;
8087   else if (arches != NULL)
8088     elf_flags = gdbarch_tdep (arches->gdbarch)->elf_flags;
// in the case when using remote debugging and manual adjustment of the
architecture value of elf_flags = 0
// Here we can check the existence of a gdbarch->bfd_arch_info structure
and adjust the elf_flag as if it was read from a real elf file.
8089   else
8090     elf_flags = 0;
8091   if (gdbarch_debug)
8092     fprintf_unfiltered (gdb_stdlog,
8093             "mips_gdbarch_init: elf_flags = 0x%08x\n", elf_flags);

Further, on the basis of elf_flag, we get the correct type of ABI. In this
case, this solution is for mips only.



ср, 17 окт. 2018 г. в 16:02, 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
>


-- 
Sincerely, Denis Dmitriev.