[PATCH] Allow osabi to be optional in target descriptors

[Alan Hayward <Alan.Hayward@arm.com>]

Osabi is an option field in target descriptors, according to:
https://sourceware.org/gdb/current/onlinedocs/gdb/Target-Description-Format.html

However, removing the osabi field from the i386 and amd64 target descriptors
will cause gdbserver to assert. This is code I used to test (not for
committing!) :

diff --git a/gdb/arch/amd64.c b/gdb/arch/amd64.c
index 30c73e642f..5c63a6c223 100644
--- a/gdb/arch/amd64.c
+++ b/gdb/arch/amd64.c
@@ -41,9 +41,6 @@ amd64_create_target_description (uint64_t xcr0, bool is_x32, bool is_linux)

 #ifndef IN_PROCESS_AGENT
   set_tdesc_architecture (tdesc, is_x32 ? "i386:x64-32" : "i386:x86-64");
-
-  if (is_linux)
-    set_tdesc_osabi (tdesc, "GNU/Linux");
 #endif

   long regnum = 0;
diff --git a/gdb/arch/i386.c b/gdb/arch/i386.c
index 7d71506a7b..112c0a89e6 100644
--- a/gdb/arch/i386.c
+++ b/gdb/arch/i386.c
@@ -37,8 +37,6 @@ i386_create_target_description (uint64_t xcr0, bool is_linux)

 #ifndef IN_PROCESS_AGENT
   set_tdesc_architecture (tdesc, "i386");
-  if (is_linux)
-    set_tdesc_osabi (tdesc, "GNU/Linux");
 #endif

   long regnum = 0;


The following patch fixes this error.

Tested with gdbserver on x86 and also on aarch64 with my target descriptor patch.
Also ran make check on x86 with unix and native-gdbserver.


2017-11-16  Alan Hayward  <alan.hayward@arm.com>

gdbserver
	* tdesc.c (tdesc_get_features_xml): Allow null osabi.


diff --git a/gdb/gdbserver/tdesc.c b/gdb/gdbserver/tdesc.c
index 63d6467d56d168777f4fa39b56495dd5649c046b..72603d626f005821a8b866d60cfdfca112c1395c 100644
--- a/gdb/gdbserver/tdesc.c
+++ b/gdb/gdbserver/tdesc.c
@@ -92,8 +92,7 @@ tdesc_get_features_xml (target_desc *tdesc)
   /* Either .xmltarget or .features is not NULL.  */
   gdb_assert (tdesc->xmltarget != NULL
 	      || (tdesc->features != NULL
-		  && tdesc->arch != NULL
-		  && tdesc->osabi != NULL));
+		  && tdesc->arch != NULL));

   if (tdesc->xmltarget == NULL)
     {
@@ -105,9 +104,12 @@ tdesc_get_features_xml (target_desc *tdesc)
       buffer += tdesc->arch;
       buffer += "</architecture>";

-      buffer += "<osabi>";
-      buffer += tdesc->osabi;
-      buffer += "</osabi>";
+      if (tdesc->osabi != NULL)
+	{
+	  buffer += "<osabi>";
+	  buffer += tdesc->osabi;
+	  buffer += "</osabi>";
+	}

       char *xml;