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

[Aleksandar Ristovski <aristovski@qnx.com>]

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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