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

Aleksandar Ristovski
2015-10-21T13:34:13Z

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On 15-10-21 05:49 AM, Pedro Alves wrote:
...
>> + 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;

Done.

>
>> + 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.

Comment removed.

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

Done.

...
>> + {
>> + note = alloca (sectsize);
>
> For C++, write:
>
> note = (char *) alloca (sectsize);

Used XNEWVEC/XDELETEVEC instead.

>
>
>> + 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?

Removed. Rely on new sniffing only, no hard coded fallback.

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

New version of the patch attached.

Thank you,

Aleksandar Ristovski

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From 6df97e71696e47d85000413bf4a97cf5d43b11f1 Mon Sep 17 00:00:00 2001
From: Aleksandar Ristovski <aristovski@qnx.com>
Date: Wed, 21 Oct 2015 09:29:54 -0400
Subject: [PATCH 2/2] [nto] Improve ABI sniffing.

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 | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 52 insertions(+), 3 deletions(-)

diff --git a/gdb/nto-tdep.c b/gdb/nto-tdep.c
index e50d302..4e0cc84 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 +335,58 @@ 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;
+ /* 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);
+
+ if (sectsize > 128)
+ sectsize = 128;
+
+ if (sectname != NULL && strstr (sectname, QNX_INFO_SECT_NAME) != NULL)
+ *(enum gdb_osabi *) obj = GDB_OSABI_QNXNTO;
+
+ if (sectname != NULL && strstr (sectname, "note") != NULL)
+ {
+ const unsigned sizeof_Elf_Nhdr = 12;
+
+ note = XNEWVEC (char, sectsize);
+ bfd_get_section_contents (abfd, sect, note, 0, sectsize);
+ namelen = (unsigned int) bfd_h_get_32 (abfd, note);
+ name = note + sizeof_Elf_Nhdr;
+ if (sectsize < namelen + sizeof_Elf_Nhdr
+ || namelen > sizeof (QNX_NOTE_NAME) + 1)
+ {
+ /* Can not be QNX note. */
+ XDELETEVEC (note);
+ return;
+ }
+
+ if (namelen > 0 && 0 == strcmp (name, QNX_NOTE_NAME))
+ *(enum gdb_osabi *) obj = GDB_OSABI_QNXNTO;
+
+ XDELETEVEC (note);
+ }
+}
+
enum gdb_osabi
nto_elf_osabi_sniffer (bfd *abfd)
{
- if (nto_is_nto_target)
- return nto_is_nto_target (abfd);
- return GDB_OSABI_UNKNOWN;
+ enum gdb_osabi osabi = GDB_OSABI_UNKNOWN;
+
+ bfd_map_over_sections (abfd,
+ nto_sniff_abi_note_section,
+ &osabi);
+
+ return osabi;
}

static const char *nto_thread_state_str[] =
--
1.9.1