[libc] Add arm 32 FEnvImpl.

Reviewed By: lntue

Differential Revision: https://reviews.llvm.org/D145347

libc/config/linux/arm/entrypoints.txt

@@ -89,6 +89,22 @@ set(TARGET_LIBC_ENTRYPOINTS
 )
 
 set(TARGET_LIBM_ENTRYPOINTS
+    # fenv.h entrypoints
+    libc.src.fenv.feclearexcept
+    libc.src.fenv.fedisableexcept
+    libc.src.fenv.feenableexcept
+    libc.src.fenv.fegetenv
+    libc.src.fenv.fegetexcept
+    libc.src.fenv.fegetexceptflag
+    libc.src.fenv.fegetround
+    libc.src.fenv.feholdexcept
+    libc.src.fenv.fesetenv
+    libc.src.fenv.fesetexceptflag
+    libc.src.fenv.fesetround
+    libc.src.fenv.feraiseexcept
+    libc.src.fenv.fetestexcept
+    libc.src.fenv.feupdateenv
+
     # math.h entrypoints
     libc.src.math.fabs
     libc.src.math.fabsf

libc/src/__support/FPUtil/FEnvImpl.h

@@ -28,6 +28,8 @@
 // the apple condition here should be removed.
 #elif defined(LIBC_TARGET_ARCH_IS_X86) && !defined(__APPLE__)
 #include "x86_64/FEnvImpl.h"
+#elif defined(LIBC_TARGET_ARCH_IS_ARM)
+#include "arm/FEnvImpl.h"
 #else
 
 namespace __llvm_libc::fputil {

libc/src/__support/FPUtil/arm/FEnvImpl.h

@@ -0,0 +1,265 @@
+//===-- arm floating point env manipulation functions -----------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SUPPORT_FPUTIL_ARM_FENVIMPL_H
+#define LLVM_LIBC_SRC_SUPPORT_FPUTIL_ARM_FENVIMPL_H
+
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/macros/config.h" // For LIBC_INLINE
+
+#include <fenv.h>
+#include <stdint.h>
+
+namespace __llvm_libc {
+namespace fputil {
+
+struct FEnv {
+  // Arm floating point state is all stored in a single 32-bit register named
+  // fpscr.
+  uint32_t fpscr;
+  static constexpr uint32_t RoundingControlBitPosition = 22;
+  static constexpr uint32_t ExceptionControlBitPosition = 8;
+
+  static constexpr uint32_t TONEAREST = 0x0;
+  static constexpr uint32_t UPWARD = 0x1;
+  static constexpr uint32_t DOWNWARD = 0x2;
+  static constexpr uint32_t TOWARDZERO = 0x3;
+
+  static constexpr uint32_t INVALID_ENABLE = 0x1;
+  static constexpr uint32_t DIVBYZERO_ENABLE = 0x2;
+  static constexpr uint32_t OVERFLOW_ENABLE = 0x4;
+  static constexpr uint32_t UNDERFLOW_ENABLE = 0x8;
+  static constexpr uint32_t INEXACT_ENABLE = 0x10;
+  static constexpr uint32_t DENORMAL_ENABLE = 0x20;
+
+  static constexpr uint32_t INVALID_STATUS = 0x1;
+  static constexpr uint32_t DIVBYZERO_STATUS = 0x2;
+  static constexpr uint32_t OVERFLOW_STATUS = 0x4;
+  static constexpr uint32_t UNDERFLOW_STATUS = 0x8;
+  static constexpr uint32_t INEXACT_STATUS = 0x10;
+  static constexpr uint32_t DENORMAL_STATUS = 0x80;
+
+  LIBC_INLINE static uint32_t get_fpscr() { return __builtin_arm_get_fpscr(); }
+  LIBC_INLINE static void set_fpscr(uint32_t val) {
+    __builtin_arm_set_fpscr(val);
+  }
+
+  LIBC_INLINE static int exception_enable_bits_to_macro(uint32_t status) {
+    return (status & INVALID_ENABLE ? FE_INVALID : 0) |
+           (status & DIVBYZERO_ENABLE ? FE_DIVBYZERO : 0) |
+           (status & OVERFLOW_ENABLE ? FE_OVERFLOW : 0) |
+           (status & UNDERFLOW_ENABLE ? FE_UNDERFLOW : 0) |
+           (status & INEXACT_ENABLE ? FE_INEXACT : 0);
+  }
+
+  LIBC_INLINE static uint32_t exception_macro_to_enable_bits(int except) {
+    return (except & FE_INVALID ? INVALID_ENABLE : 0) |
+           (except & FE_DIVBYZERO ? DIVBYZERO_ENABLE : 0) |
+           (except & FE_OVERFLOW ? OVERFLOW_ENABLE : 0) |
+           (except & FE_UNDERFLOW ? UNDERFLOW_ENABLE : 0) |
+           (except & FE_INEXACT ? INEXACT_ENABLE : 0);
+  }
+
+  LIBC_INLINE static uint32_t exception_macro_to_status_bits(int except) {
+    return (except & FE_INVALID ? INVALID_STATUS : 0) |
+           (except & FE_DIVBYZERO ? DIVBYZERO_STATUS : 0) |
+           (except & FE_OVERFLOW ? OVERFLOW_STATUS : 0) |
+           (except & FE_UNDERFLOW ? UNDERFLOW_STATUS : 0) |
+           (except & FE_INEXACT ? INEXACT_STATUS : 0);
+  }
+
+  LIBC_INLINE static uint32_t exception_status_bits_to_macro(int status) {
+    return (status & INVALID_STATUS ? FE_INVALID : 0) |
+           (status & DIVBYZERO_STATUS ? FE_DIVBYZERO : 0) |
+           (status & OVERFLOW_STATUS ? FE_OVERFLOW : 0) |
+           (status & UNDERFLOW_STATUS ? FE_UNDERFLOW : 0) |
+           (status & INEXACT_STATUS ? FE_INEXACT : 0);
+  }
+};
+
+// Enables exceptions in |excepts| and returns the previously set exceptions.
+LIBC_INLINE int enable_except(int excepts) {
+  uint32_t new_excepts = FEnv::exception_macro_to_enable_bits(excepts);
+  uint32_t fpscr = FEnv::get_fpscr();
+  int old = (fpscr >> FEnv::ExceptionControlBitPosition) & 0x3F;
+  fpscr |= (new_excepts << FEnv::ExceptionControlBitPosition);
+  FEnv::set_fpscr(fpscr);
+  return FEnv::exception_enable_bits_to_macro(old);
+}
+
+// Disables exceptions in |excepts| and returns the previously set exceptions.
+LIBC_INLINE int disable_except(int excepts) {
+  uint32_t disable_bits = FEnv::exception_macro_to_enable_bits(excepts);
+  uint32_t fpscr = FEnv::get_fpscr();
+  int old = (fpscr >> FEnv::ExceptionControlBitPosition) & 0x3F;
+  fpscr &= ~(disable_bits << FEnv::ExceptionControlBitPosition);
+  FEnv::set_fpscr(fpscr);
+  return FEnv::exception_enable_bits_to_macro(old);
+}
+
+// Returns the currently enabled exceptions.
+LIBC_INLINE int get_except() {
+  uint32_t fpscr = FEnv::get_fpscr();
+  int enabled_excepts = (fpscr >> FEnv::ExceptionControlBitPosition) & 0x3F;
+  return FEnv::exception_enable_bits_to_macro(enabled_excepts);
+}
+
+// Clears the exceptions in |excepts|.
+LIBC_INLINE int clear_except(int excepts) {
+  uint32_t fpscr = FEnv::get_fpscr();
+  uint32_t to_clear = FEnv::exception_macro_to_status_bits(excepts);
+  fpscr &= ~to_clear;
+  FEnv::set_fpscr(fpscr);
+  return 0;
+}
+
+// Returns the set of exceptions which are from the input set |excepts|.
+LIBC_INLINE int test_except(int excepts) {
+  uint32_t to_test = FEnv::exception_macro_to_status_bits(excepts);
+  uint32_t fpscr = FEnv::get_fpscr();
+  return FEnv::exception_status_bits_to_macro(fpscr & 0x9F & to_test);
+}
+
+// Set the exceptions in |excepts|.
+LIBC_INLINE int set_except(int excepts) {
+  uint32_t fpscr = FEnv::get_fpscr();
+  FEnv::set_fpscr(fpscr | FEnv::exception_macro_to_status_bits(excepts));
+  return 0;
+}
+
+LIBC_INLINE int raise_except(int excepts) {
+  float zero = 0.0f;
+  float one = 1.0f;
+  float large_value = float(FPBits<float>(FPBits<float>::MAX_NORMAL));
+  float small_value = float(FPBits<float>(FPBits<float>::MIN_NORMAL));
+  auto divfunc = [](float a, float b) {
+    __asm__ __volatile__("flds  s0, %0\n\t"
+                         "flds  s1, %1\n\t"
+                         "fdivs s0, s0, s1\n\t"
+                         : // No outputs
+                         : "m"(a), "m"(b)
+                         : "s0", "s1" /* s0 and s1 are clobbered */);
+  };
+
+  uint32_t to_raise = FEnv::exception_macro_to_status_bits(excepts);
+  int result = 0;
+
+  if (to_raise & FEnv::INVALID_STATUS) {
+    divfunc(zero, zero);
+    uint32_t fpscr = FEnv::get_fpscr();
+    if (!(fpscr & FEnv::INVALID_STATUS))
+      result = -1;
+  }
+  if (to_raise & FEnv::DIVBYZERO_STATUS) {
+    divfunc(one, zero);
+    uint32_t fpscr = FEnv::get_fpscr();
+    if (!(fpscr & FEnv::DIVBYZERO_STATUS))
+      result = -1;
+  }
+  if (to_raise & FEnv::OVERFLOW_STATUS) {
+    divfunc(large_value, small_value);
+    uint32_t fpscr = FEnv::get_fpscr();
+    if (!(fpscr & FEnv::OVERFLOW_STATUS))
+      result = -1;
+  }
+  if (to_raise & FEnv::UNDERFLOW_STATUS) {
+    divfunc(small_value, large_value);
+    uint32_t fpscr = FEnv::get_fpscr();
+    if (!(fpscr & FEnv::UNDERFLOW_STATUS))
+      result = -1;
+  }
+  if (to_raise & FEnv::INEXACT_STATUS) {
+    float two = 2.0f;
+    float three = 3.0f;
+    // 2.0 / 3.0 cannot be represented exactly in any radix 2 floating point
+    // format.
+    divfunc(two, three);
+    uint32_t fpscr = FEnv::get_fpscr();
+    if (!(fpscr & FEnv::INEXACT_STATUS))
+      result = -1;
+  }
+  return result;
+}
+
+LIBC_INLINE int get_round() {
+  uint32_t mode = (FEnv::get_fpscr() >> FEnv::RoundingControlBitPosition) & 0x3;
+  switch (mode) {
+  case FEnv::TONEAREST:
+    return FE_TONEAREST;
+  case FEnv::DOWNWARD:
+    return FE_DOWNWARD;
+  case FEnv::UPWARD:
+    return FE_UPWARD;
+  case FEnv::TOWARDZERO:
+    return FE_TOWARDZERO;
+  default:
+    return -1; // Error value.
+  }
+  return 0;
+}
+
+LIBC_INLINE int set_round(int mode) {
+  uint16_t bits;
+  switch (mode) {
+  case FE_TONEAREST:
+    bits = FEnv::TONEAREST;
+    break;
+  case FE_DOWNWARD:
+    bits = FEnv::DOWNWARD;
+    break;
+  case FE_UPWARD:
+    bits = FEnv::UPWARD;
+    break;
+  case FE_TOWARDZERO:
+    bits = FEnv::TOWARDZERO;
+    break;
+  default:
+    return 1; // To indicate failure
+  }
+
+  uint32_t fpscr = FEnv::get_fpscr();
+  fpscr &= ~(0x3 << FEnv::RoundingControlBitPosition);
+  fpscr |= (bits << FEnv::RoundingControlBitPosition);
+  FEnv::set_fpscr(fpscr);
+
+  return 0;
+}
+
+LIBC_INLINE int get_env(fenv_t *envp) {
+  FEnv *state = reinterpret_cast<FEnv *>(envp);
+  state->fpscr = FEnv::get_fpscr();
+  return 0;
+}
+
+LIBC_INLINE int set_env(const fenv_t *envp) {
+  if (envp == FE_DFL_ENV) {
+    uint32_t fpscr = FEnv::get_fpscr();
+    // Default status implies:
+    // 1. Round to nearest rounding mode.
+    fpscr &= ~(0x3 << FEnv::RoundingControlBitPosition);
+    fpscr |= (FEnv::TONEAREST << FEnv::RoundingControlBitPosition);
+    // 2. All exceptions are disabled.
+    fpscr &= ~(0x3F << FEnv::ExceptionControlBitPosition);
+    // 3. All exceptions are cleared. There are two reserved bits
+    // at bit 5 and 6 so we just write one full byte (6 bits for
+    // the exceptions, and 2 reserved bits.)
+    fpscr &= ~(static_cast<uint32_t>(0xFF));
+
+    FEnv::set_fpscr(fpscr);
+    return 0;
+  }
+
+  const FEnv *state = reinterpret_cast<const FEnv *>(envp);
+  FEnv::set_fpscr(state->fpscr);
+  return 0;
+}
+
+} // namespace fputil
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SUPPORT_FPUTIL_ARM_FENVIMPL_H

libc/test/src/fenv/enabled_exceptions_test.cpp

@@ -21,8 +21,8 @@
 // This test enables an exception and verifies that raising that exception
 // triggers SIGFPE.
 TEST(LlvmLibcExceptionStatusTest, RaiseAndCrash) {
-#if defined(LIBC_TARGET_ARCH_IS_AARCH64)
-  // Few aarch64 HW implementations do not trap exceptions. We skip this test
+#if defined(LIBC_TARGET_ARCH_IS_ANY_ARM)
+  // Few Arm HW implementations do not trap exceptions. We skip this test
   // completely on such HW.
   //
   // Whether HW supports trapping exceptions or not is deduced by enabling an
@@ -33,7 +33,7 @@ TEST(LlvmLibcExceptionStatusTest, RaiseAndCrash) {
   __llvm_libc::fputil::enable_except(FE_DIVBYZERO);
   if (__llvm_libc::fputil::get_except() == 0)
     return;
-#endif // defined(LIBC_TARGET_ARCH_IS_AARCH64)
+#endif // defined(LIBC_TARGET_ARCH_IS_ANY_ARM)
 
   // TODO: Install a floating point exception handler and verify that the
   // the expected exception was raised. One will have to longjmp back from

libc/test/src/fenv/feenableexcept_test.cpp

@@ -16,8 +16,8 @@
 #include <fenv.h>
 
 TEST(LlvmLibcFEnvTest, EnableTest) {
-#if defined(LIBC_TARGET_ARCH_IS_AARCH64)
-  // Few aarch64 HW implementations do not trap exceptions. We skip this test
+#if defined(LIBC_TARGET_ARCH_IS_ANY_ARM)
+  // Few Arm HW implementations do not trap exceptions. We skip this test
   // completely on such HW.
   //
   // Whether HW supports trapping exceptions or not is deduced by enabling an
@@ -28,7 +28,7 @@ TEST(LlvmLibcFEnvTest, EnableTest) {
   __llvm_libc::feenableexcept(FE_DIVBYZERO);
   if (__llvm_libc::fegetexcept() == 0)
     return;
-#endif // defined(LIBC_TARGET_ARCH_IS_AARCH64)
+#endif // defined(LIBC_TARGET_ARCH_IS_ANY_ARM)
 
   int excepts[] = {FE_DIVBYZERO, FE_INVALID, FE_INEXACT, FE_OVERFLOW,
                    FE_UNDERFLOW};

libc/test/src/fenv/feholdexcept_test.cpp

@@ -16,8 +16,8 @@
 #include <fenv.h>
 
 TEST(LlvmLibcFEnvTest, RaiseAndCrash) {
-#if defined(LIBC_TARGET_ARCH_IS_AARCH64)
-  // Few aarch64 HW implementations do not trap exceptions. We skip this test
+#if defined(LIBC_TARGET_ARCH_IS_ANY_ARM)
+  // Few Arm HW implementations do not trap exceptions. We skip this test
   // completely on such HW.
   //
   // Whether HW supports trapping exceptions or not is deduced by enabling an
@@ -28,7 +28,7 @@ TEST(LlvmLibcFEnvTest, RaiseAndCrash) {
   __llvm_libc::fputil::enable_except(FE_DIVBYZERO);
   if (__llvm_libc::fputil::get_except() == 0)
     return;
-#endif // defined(LIBC_TARGET_ARCH_IS_AARCH64)
+#endif // defined(LIBC_TARGET_ARCH_IS_ANY_ARM)
 
   int excepts[] = {FE_DIVBYZERO, FE_INVALID, FE_INEXACT, FE_OVERFLOW,
                    FE_UNDERFLOW};