Re: [PATCH 2/2] [nto] Improve ABI sniffing.

Pedro Alves
2015-10-21T09:49:43Z

On 10/20/2015 07:10 PM, Aleksandar Ristovski wrote:
> Use qnx specific notes to figure out the OS.
>
> gdb/ChangeLog:
> * gdb/nto-tdep.c (QNX_NOTE_NAME, QNX_INFO_SECT_NAME): New defines.
> (nto_sniff_abi_note_section): New function.
> (nto_elf_osabi_sniffer): Use new function to recognize nto specific
> binary.
> ---
> gdb/nto-tdep.c | 46 ++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 44 insertions(+), 2 deletions(-)
>
> diff --git a/gdb/nto-tdep.c b/gdb/nto-tdep.c
> index e50d302..48826cb 100644
> --- a/gdb/nto-tdep.c
> +++ b/gdb/nto-tdep.c
> @@ -32,6 +32,9 @@
> #include "gdbcore.h"
> #include "objfiles.h"
>
> +#define QNX_NOTE_NAME "QNX"
> +#define QNX_INFO_SECT_NAME "QNX_info"
> +
> #ifdef __CYGWIN__
> #include <sys/cygwin.h>
> #endif
> @@ -332,12 +335,51 @@ nto_dummy_supply_regset (struct regcache *regcache, char *regs)
> /* Do nothing. */
> }
>
> +static void
> +nto_sniff_abi_note_section (bfd *abfd, asection *sect, void *obj)
> +{
> + const char *sectname;
> + unsigned int sectsize;
> + char *note; // buffer holding the section contents

Please use /**/ format for comments, and write full sentences - start
with uppercase, period at end. Usually that leads to putting the comment
above, e.g.:

+ /* Buffer holding the section contents. */
+ char *note;

> + unsigned int namelen;
> + const char *name;
> +
> + sectname = bfd_get_section_name (abfd, sect);
> + sectsize = bfd_section_size (abfd, sect);
> +
> + /* TODO: limit the note size here, for now limit is 128 bytes
> + (enough to check the name and type). */

This reads like limiting is left to do, but then it does
implement a limit. So this TODO comment is confusing.

You should also make sure the section is the at least
the minimum size you expect though.

> + if (sectsize > 128)
> + sectsize = 128;
> +
> + if (sectname && strstr (sectname, QNX_INFO_SECT_NAME) != NULL)
> + *(enum gdb_osabi *) obj = GDB_OSABI_QNXNTO;
> +

sectname != NULL

> + if (sectname && strstr (sectname, "note") != NULL)

sectname != NULL

> + {
> + note = alloca (sectsize);

For C++, write:

note = (char *) alloca (sectsize);

> + bfd_get_section_contents (abfd, sect, note, 0, sectsize);
> + namelen = (unsigned int) bfd_h_get_32 (abfd, note);
> + name = note + 12;
> +
> + if (namelen > 0
> + && (0 == strcmp (name, QNX_NOTE_NAME)))
> + *(enum gdb_osabi *) obj = GDB_OSABI_QNXNTO;
> + }
> +}
> +
> enum gdb_osabi
> nto_elf_osabi_sniffer (bfd *abfd)
> {
> - if (nto_is_nto_target)
> + enum gdb_osabi osabi = GDB_OSABI_UNKNOWN;
> +
> + bfd_map_over_sections (abfd,
> + nto_sniff_abi_note_section,
> + &osabi);
> +
> + if (osabi == GDB_OSABI_UNKNOWN && nto_is_nto_target)
> return nto_is_nto_target (abfd);

...
nto_is_nto_target = procfs_is_nto_target;
...

static enum gdb_osabi
procfs_is_nto_target (bfd *abfd)
{
return GDB_OSABI_QNXNTO;
}

So that basically could be rewritten as:

if (osabi == GDB_OSABI_UNKNOWN && nto_is_nto_target)
return GDB_OSABI_QNXNTO;

But, do we still need this nto_is_nto_target hack here?
Now with proper sniffing, can't we just remove it altogether?

> - return GDB_OSABI_UNKNOWN;
> + return osabi;
> }
>
> static const char *nto_thread_state_str[] =
>

Thanks,
Pedro Alves