[PATCH 1/2] AArch64 AAPCS: Empty structs have non zero size in C++

[Alan Hayward <Alan dot Hayward at arm dot com>]

When gdb.base/infcall-nested-structs.c is complied as C++, the structs
containing empty structs are no longer passed via float arguments.

This is because structs in C++ have a minimum size of 1.  This can then
cause padding in the struct, which is disallowed for AAPCS.

Add padding checks to AArch64 and add C++ compile variant to the test.

gdb/ChangeLog:

2019-01-16  Alan Hayward  <alan.hayward@arm.com>

	* aarch64-tdep.c (aapcs_is_vfp_call_or_return_candidate_1): Check
	for padding.

gdb/testsuite/ChangeLog:

2019-01-16  Alan Hayward  <alan.hayward@arm.com>

	* gdb.base/infcall-nested-structs.exp: Test C++ in addition to C.
---
 gdb/aarch64-tdep.c                            |  8 ++++
 .../gdb.base/infcall-nested-structs.exp       | 42 +++++++++++++------
 2 files changed, 38 insertions(+), 12 deletions(-)

diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
index 407adc8a42..ff6ca5c6e0 100644
--- a/gdb/aarch64-tdep.c
+++ b/gdb/aarch64-tdep.c
@@ -1392,6 +1392,14 @@ aapcs_is_vfp_call_or_return_candidate_1 (struct type *type,
 	      return -1;
 	    count += sub_count;
 	  }
+
+	/* Ensure there is no padding between the fields (allowing for empty
+	   zero length structs)  */
+	int ftype_length = (*fundamental_type == nullptr)
+			   ? 0 : TYPE_LENGTH (*fundamental_type);
+	if (count * ftype_length != TYPE_LENGTH (type))
+	  return -1;
+
 	return count;
       }
 
diff --git a/gdb/testsuite/gdb.base/infcall-nested-structs.exp b/gdb/testsuite/gdb.base/infcall-nested-structs.exp
index b10e6d21eb..543702ac9a 100644
--- a/gdb/testsuite/gdb.base/infcall-nested-structs.exp
+++ b/gdb/testsuite/gdb.base/infcall-nested-structs.exp
@@ -24,6 +24,20 @@ if [target_info exists gdb,cannot_call_functions] {
     continue
 }
 
+# Only test C++ if we are able.  Always use C.
+if { [skip_cplus_tests] || [get_compiler_info "c++"] } {
+    set lang {c}
+} else {
+    set lang {c c++}
+}
+
+foreach l $lang {
+    set dir "$l"
+    remote_exec build "rm -rf [standard_output_file ${dir}]"
+    remote_exec build "mkdir -p [standard_output_file ${dir}]"
+}
+
+
 set int_types { tc ts ti tl tll }
 set float_types { tf td tld }
 set complex_types { tfc tdc tldc }
@@ -44,7 +58,7 @@ proc I2A { n } {
 # types of the struct fields within the source.  Run up to main.
 # Also updates the global "testfile" to reflect the most recent build.
 
-proc start_nested_structs_test { types } {
+proc start_nested_structs_test { lang types } {
     global testfile
     global srcfile
     global binfile
@@ -53,9 +67,11 @@ proc start_nested_structs_test { types } {
     global compile_flags
 
     standard_testfile .c
+    set dir "$lang"
 
     # Create the additional flags
     set flags $compile_flags
+    lappend flags $lang
 
     for {set n 0} {$n<[llength ${types}]} {incr n} {
 	set m [I2A ${n}]
@@ -64,7 +80,7 @@ proc start_nested_structs_test { types } {
 	append testfile "-" "$t"
     }
 
-    set binfile [standard_output_file ${testfile}]
+    set binfile [standard_output_file ${dir}/${testfile}]
     if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable "${flags}"] != "" } {
 	unresolved "failed to compile"
 	return 0
@@ -125,48 +141,50 @@ proc run_tests {} {
 # Set up a test prefix, compile the test binary, run to main, and then
 # run some tests.
 
-proc start_gdb_and_run_tests { types } {
+proc start_gdb_and_run_tests { lang types } {
     set prefix "types"
 
     foreach t $types {
 	append prefix "-" "${t}"
     }
 
-    with_test_prefix $prefix {
-	if { [start_nested_structs_test $types] } {
-	    run_tests
+    foreach_with_prefix l $lang {
+	with_test_prefix $prefix {
+	    if { [start_nested_structs_test $l $types] } {
+		run_tests
+	    }
 	}
     }
 }
 
 foreach ta $int_types {
-    start_gdb_and_run_tests $ta
+    start_gdb_and_run_tests $lang $ta
 }
 
 if [support_complex_tests] {
     foreach ta $complex_types {
-	start_gdb_and_run_tests $ta
+	start_gdb_and_run_tests $lang $ta
     }
 }
 
 if ![gdb_skip_float_test] {
     foreach ta $float_types {
-	start_gdb_and_run_tests $ta
+	start_gdb_and_run_tests $lang $ta
     }
 
     foreach ta $int_types {
 	foreach tb $float_types {
-	    start_gdb_and_run_tests [list $ta $tb]
+	    start_gdb_and_run_tests $lang [list $ta $tb]
 	}
     }
 
     foreach ta $float_types {
 	foreach tb $int_types {
-	    start_gdb_and_run_tests [list $ta $tb]
+	    start_gdb_and_run_tests $lang [list $ta $tb]
 	}
 
 	foreach tb $float_types {
-	    start_gdb_and_run_tests [list $ta $tb]
+	    start_gdb_and_run_tests $lang [list $ta $tb]
 	}
     }
 }
-- 
2.17.2 (Apple Git-113)