Fix wrong output of x87 registers due to truncation to double on amd64

When `info float` is used on an AMD64 system, GDB prints
floating-point values of x87 registers with raw contents like
0x361a867a8e0527397ce0 or 0xc4f988454a1ddd3cfdab wrongly.

This happens due to truncation to double, after which the former
becomes 0.0, and the latter becomes negative infinity.  This is caused
by failed detection of x86-64 host, which results in setting
gdb_host_{float,double,long_double}_format to zeros.

This commit fixes this misdetection, and adds a test to make sure
future commits don't introduce a regression here.

gdb/ChangeLog:
2015-12-09  Ruslan Kabatsayev  <b7.10110111@gmail.com>

	PR gdb/18702
	* configure.host: Fix detection of x86_64 host when setting
	floatformats.

gdb/testsuite/ChangeLog:
2015-12-09  Ruslan Kabatsayev  <b7.10110111@gmail.com>
	    Pedro Alves  <pedro@redhat.com>

	PR gdb/18702
	Add checking of floatformats setup on x86_64 hosts.
	* gdb.arch/i386-float.S (main): Load bigval and smallval.
	(smallval, bigval): New labels/constants.
	* gdb.arch/i386-float.exp: Use with_test_prefix and test "info
	float" after loading bigval and smallval.

5 files changed, 37 insertions, 5 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index b5d2431..8a8202c 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2015-12-09  Ruslan Kabatsayev  <b7.10110111@gmail.com>  (tiny patch)
+
+	PR gdb/18702
+	* configure.host: Fix detection of x86_64 host when setting
+	floatformats.
+
 2015-12-08  Pierre-Marie de Rodat  <derodat@adacore.com>
 
 	* NEWS: Announce this enhancement and the corresponding new
diff --git a/gdb/configure.host b/gdb/configure.host
index 48714f4..ef265eb 100644
--- a/gdb/configure.host
+++ b/gdb/configure.host
@@ -195,7 +195,7 @@ esac
 # "double" and "long double" types.
 
 case "${host}" in
-i[34567]86-*-*)
+i[34567]86-*-*|x86_64-*-*)
 	gdb_host_float_format="&floatformat_ieee_single_little"
 	gdb_host_double_format="&floatformat_ieee_double_little"
 	gdb_host_long_double_format="&floatformat_i387_ext"
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 8316d32..d959e7b 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,13 @@
+2015-12-09  Ruslan Kabatsayev  <b7.10110111@gmail.com>
+	    Pedro Alves  <pedro@redhat.com>
+
+	PR gdb/18702
+	Add checking of floatformats setup on x86_64 hosts.
+	* gdb.arch/i386-float.S (main): Load bigval and smallval.
+	(smallval, bigval): New labels/constants.
+	* gdb.arch/i386-float.exp: Use with_test_prefix and test "info
+	float" after loading bigval and smallval.
+
 2015-12-07  Pierre-Marie de Rodat  <derodat@adacore.com>
 
 	* gdb.ada/fun_overload_menu.exp: New testcase.
diff --git a/gdb/testsuite/gdb.arch/i386-float.S b/gdb/testsuite/gdb.arch/i386-float.S
index 76126c4..f5de8c2 100644
--- a/gdb/testsuite/gdb.arch/i386-float.S
+++ b/gdb/testsuite/gdb.arch/i386-float.S
@@ -29,6 +29,10 @@
 SYMBOL(main):
 	fninit
 	fldt    val
+	fldt    bigval
+	fldt    smallval
 	ret
 .data
 	val: .byte 0x00,0x00,0x45,0x07,0x11,0x19,0x22,0xe9,0xfe,0xbf
+	smallval: .byte 0xe9,0xd0,0xd7,0x65,0x81,0xb7,0x43,0xc6,0x5c,0x6a
+	bigval:   .byte 0x6a,0x45,0x90,0xdc,0x03,0xc1,0xf8,0xc6,0xe5,0x03
diff --git a/gdb/testsuite/gdb.arch/i386-float.exp b/gdb/testsuite/gdb.arch/i386-float.exp
index e638ceb..e3ae3ba 100644
--- a/gdb/testsuite/gdb.arch/i386-float.exp
+++ b/gdb/testsuite/gdb.arch/i386-float.exp
@@ -37,7 +37,19 @@ if ![runto_main] then {
     return 0
 }
 
-gdb_test "stepi" ".*fldt.*" "first stepi"
-gdb_test "info float" ".*R7: Empty   0x00000000000000000000\r\n.*"
-gdb_test "stepi" ".*ret.*" "second stepi"
-gdb_test "info float" ".*=>R7: Valid   0xbffee922191107450000 .*"
+with_test_prefix "zero" {
+    gdb_test "stepi" ".*fldt.*"
+    gdb_test "info float" "R7: Empty   0x00000000000000000000\r\n.*"
+}
+with_test_prefix "val" {
+    gdb_test "stepi" ".*fldt.*"
+    gdb_test "info float" "=>R7: Valid   0xbffee922191107450000 .*"
+}
+with_test_prefix "smallval" {
+    gdb_test "stepi" ".*fldt.*"
+    gdb_test "info float" "=>R6: Valid   0x03e5c6f8c103dc90456a \\+3.500000000000000007e-4632\r\n.*"
+}
+with_test_prefix "bigval" {
+    gdb_test "stepi" ".*ret.*"
+    gdb_test "info float" "=>R5: Valid   0x6a5cc643b78165d7d0e9 \\+7.250000000000000005e\\+3264\r\n.*"
+}