host: preserve IEEE denormal assumptions in compiler wrappers

host/bin/prospero-clang

@@ -75,6 +75,7 @@ exec -a "${SCRIPT_NAME}" "${SCRIPT_DIR}/clang" \
      -L "${PS5_PAYLOAD_SDK}/target/lib" \
      -L "${PS5_PAYLOAD_HBROOT}/lib" \
      -fno-stack-protector -fno-plt -femulated-tls \
+     -fdenormal-fp-math=ieee \
      $LIBS_C  \
      --end-no-unused-arguments \
      "$@" \

host/bin/prospero-clang++

@@ -80,6 +80,7 @@ exec -a "${SCRIPT_NAME}" "${SCRIPT_DIR}/clang++" \
      -L "${PS5_PAYLOAD_SDK}/target/lib" \
      -L "${PS5_PAYLOAD_HBROOT}/lib" \
      -fno-stack-protector -fno-plt -femulated-tls \
+     -fdenormal-fp-math=ieee \
      -frtti -fexceptions \
      $LIBS_CXX $LIBS_C \
      --end-no-unused-arguments \

samples/test_denormals/Makefile

@@ -0,0 +1,48 @@
+#   Copyright (C) 2023 John Törnblom
+#
+# This file is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; see the file COPYING. If not see
+# <http://www.gnu.org/licenses/>.
+
+PS5_HOST ?= ps5
+PS5_PORT ?= 9021
+
+ifdef PS5_PAYLOAD_SDK
+    include $(PS5_PAYLOAD_SDK)/toolchain/prospero.mk
+else
+    $(error PS5_PAYLOAD_SDK is undefined)
+endif
+
+ELF := test_denormals.elf
+
+CFLAGS := -Wall -Werror -g -O2
+
+all: $(ELF)
+
+$(ELF): main.c classify.c
+	$(CC) $(CFLAGS) -o $@ $^
+
+clean:
+	rm -f $(ELF)
+
+test: $(ELF)
+	$(PS5_DEPLOY) -h $(PS5_HOST) -p $(PS5_PORT) $^
+
+debug: $(ELF)
+	gdb-multiarch \
+	-ex "set architecture i386:x86-64" \
+	-ex "target extended-remote $(PS5_HOST):2159" \
+	-ex "file $(ELF)" \
+	-ex "remote put $(ELF) /data/$(ELF)" \
+	-ex "set remote exec-file /data/$(ELF)" \
+	-ex "start"

samples/test_denormals/classify.c

@@ -0,0 +1,11 @@
+/* Copyright (C) 2026 Mihawk
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+#include <math.h>
+
+/* A separate translation unit prevents constant folding at the call site. */
+int
+classify(float value) {
+  return __builtin_fpclassify(FP_NAN, FP_INFINITE, FP_NORMAL,
+                             FP_SUBNORMAL, FP_ZERO, value);
+}

samples/test_denormals/main.c

@@ -0,0 +1,24 @@
+/* Copyright (C) 2026 Mihawk
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+#include <math.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+int classify(float value);
+
+int
+main(void) {
+  unsigned previous, ieee;
+  uint32_t bits = 1; /* Smallest positive IEEE binary32 subnormal. */
+  float value;
+  memcpy(&value, &bits, sizeof(value));
+  __asm__ volatile("stmxcsr %0" : "=m"(previous));
+  ieee = previous & ~0x8040u; /* Disable FTZ and DAZ for this test. */
+  __asm__ volatile("ldmxcsr %0" : : "m"(ieee) : "memory");
+  const int actual = classify(value);
+  __asm__ volatile("ldmxcsr %0" : : "m"(previous) : "memory");
+  printf("classification=%d, expected FP_SUBNORMAL=%d\n", actual, FP_SUBNORMAL);
+  return actual != FP_SUBNORMAL;
+}