[PATCH][gdb/testsuite] Fix gdb.base/float128.exp with --with-mpfr=no

[Tom de Vries <tdevries@suse.de>]

Hi,

When configuring gdb using --with-mpfr=no and running test-case
gdb.base/float128.exp, we run into:
...
FAIL: gdb.base/float128.exp: print large128 (GDB may be missing MPFR support!)
...

Fix this by detecting that gdb was build without mpfr using the show
configuration command, and changing the FAIL into UNSUPPORTED.

Tested on x86_64-linux.

Any comments?

Thanks,
- Tom

[gdb/testsuite] Fix gdb.base/float128.exp with --with-mpfr=no

gdb/testsuite/ChangeLog:

2020-12-10  Tom de Vries  <tdevries@suse.de>

	PR testsuite/26954
	* gdb.base/float128.exp: Detect and handle no mprf support.

---
 gdb/testsuite/gdb.base/float128.exp | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/gdb/testsuite/gdb.base/float128.exp b/gdb/testsuite/gdb.base/float128.exp
index 40babcadc1..66f4d89c12 100644
--- a/gdb/testsuite/gdb.base/float128.exp
+++ b/gdb/testsuite/gdb.base/float128.exp
@@ -78,13 +78,34 @@ gdb_test "print f128" ".* = 20\\.375.*" "the value of f128 is changed to 20.375"
 # Note: If we get "inf" instead of the correct result, we may have run into
 # an internal overflow.  This typically happens on host platforms without
 # native IEEE-128 support where GDB was built without MPFR support.
+
+set mpfr_supported -1
+gdb_test_multiple "show configuration" "" {
+    -wrap -re "--with-mpfr\r\n.*" {
+       set mpfr_supported 1
+    }
+    -wrap -re "--without-mpfr\r\n.*" {
+       set mpfr_supported 0
+    }
+}
+
 set test "print large128"
 gdb_test_multiple "print large128" "$test" {
     -re ".* = 1\\.18973149535723176508575932662800702e\\+4932.*$gdb_prompt $" {
 	pass "$test"
     }
     -re ".* = inf.*$gdb_prompt $" {
-	fail "$test (GDB may be missing MPFR support!)"
+       if { $mpfr_supported == 0 } {
+	   if { [istarget "s390*-*-*"] || [istarget "powerpc*-*-*"] } {
+	       # Some of these archs have native 128-bit float support, in
+	       # which case this should be passing, even without MPFR support.
+	       fail $test
+	   } else {
+	       unsupported "$test (Missing MPFR support)"
+	   }
+       } else {
+           fail $test
+       }
     }
     -re ".*$gdb_prompt $" {
 	fail "$test"