/*
* Copyright (C) 2010 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
/* ChangeLog for this library:
*
* NDK r8d: Add android_setCpu().
*
* NDK r8c: Add new ARM CPU features: VFPv2, VFP_D32, VFP_FP16,
* VFP_FMA, NEON_FMA, IDIV_ARM, IDIV_THUMB2 and iWMMXt.
*
* Rewrite the code to parse /proc/self/auxv instead of
* the "Features" field in /proc/cpuinfo.
*
* Dynamically allocate the buffer that hold the content
* of /proc/cpuinfo to deal with newer hardware.
*
* NDK r7c: Fix CPU count computation. The old method only reported the
* number of _active_ CPUs when the library was initialized,
* which could be less than the real total.
*
* NDK r5: Handle buggy kernels which report a CPU Architecture number of 7
* for an ARMv6 CPU (see below).
*
* Handle kernels that only report 'neon', and not 'vfpv3'
* (VFPv3 is mandated by the ARM architecture is Neon is implemented)
*
* Handle kernels that only report 'vfpv3d16', and not 'vfpv3'
*
* Fix x86 compilation. Report ANDROID_CPU_FAMILY_X86 in
* android_getCpuFamily().
*
* NDK r4: Initial release
*/
#include <sys/system_properties.h>
#ifdef __arm__
#include <machine/cpu-features.h>
#endif
#include <pthread.h>
#include "cpu-features.h"
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>
static pthread_once_t g_once;
static int g_inited;
static AndroidCpuFamily g_cpuFamily;
static uint64_t g_cpuFeatures;
static int g_cpuCount;
static const int android_cpufeatures_debug = 0;
#ifdef __arm__
# define DEFAULT_CPU_FAMILY ANDROID_CPU_FAMILY_ARM
#elif defined __i386__
# define DEFAULT_CPU_FAMILY ANDROID_CPU_FAMILY_X86
#else
# define DEFAULT_CPU_FAMILY ANDROID_CPU_FAMILY_UNKNOWN
#endif
#define D(...) \
do { \
if (android_cpufeatures_debug) { \
printf(__VA_ARGS__); fflush(stdout); \
} \
} while (0)
#ifdef __i386__
static __inline__ void x86_cpuid(int func, int values[4])
{
int a, b, c, d;
/* We need to preserve ebx since we're compiling PIC code */
/* this means we can't use "=b" for the second output register */
__asm__ __volatile__ ( \
"push %%ebx\n"
"cpuid\n" \
"mov %%ebx, %1\n"
"pop %%ebx\n"
: "=a" (a), "=r" (b), "=c" (c), "=d" (d) \
: "a" (func) \
);
values[0] = a;
values[1] = b;
values[2] = c;
values[3] = d;
}
#endif
/* Get the size of a file by reading it until the end. This is needed
* because files under /proc do not always return a valid size when
* using fseek(0, SEEK_END) + ftell(). Nor can they be mmap()-ed.
*/
static int
get_file_size(const char* pathname)
{
int fd, ret, result = 0;
char buffer[256];
fd = open(pathname, O_RDONLY);
if (fd < 0) {
D("Can't open %s: %s\n", pathname, strerror(errno));
return -1;
}
for (;;) {
int ret = read(fd, buffer, sizeof buffer);
if (ret < 0) {
if (errno == EINTR)
continue;
D("Error while reading %s: %s\n", pathname, strerror(errno));
break;
}
if (ret == 0)
break;
result += ret;
}
close(fd);
return result;
}
/* Read the content of /proc/cpuinfo into a user-provided buffer.
* Return the length of the data, or -1 on error. Does *not*
* zero-terminate the content. Will not read more
* than 'buffsize' bytes.
*/
static int
read_file(const char* pathname, char* buffer, size_t buffsize)
{
int fd, count;
fd = open(pathname, O_RDONLY);
if (fd < 0) {
D("Could not open %s: %s\n", pathname, strerror(errno));
return -1;
}
count = 0;
while (count < (int)buffsize) {
int ret = read(fd, buffer + count, buffsize - count);
if (ret < 0) {
if (errno == EINTR)
continue;
D("Error while reading from %s: %s\n", pathname, strerror(errno));
if (count == 0)
count = -1;
break;
}
if (ret == 0)
break;
count += ret;
}
close(fd);
return count;
}
/* Extract the content of a the first occurence of a given field in
* the content of /proc/cpuinfo and return it as a heap-allocated
* string that must be freed by the caller.
*
* Return NULL if not found
*/
static char*
extract_cpuinfo_field(const char* buffer, int buflen, const char* field)
{
int fieldlen = strlen(field);
const char* bufend = buffer + buflen;
char* result = NULL;
int len, ignore;
const char *p, *q;
/* Look for first field occurence, and ensures it starts the line. */
p = buffer;
bufend = buffer + buflen;
for (;;) {
p = memmem(p, bufend-p, field, fieldlen);
if (p == NULL)
goto EXIT;
if (p == buffer || p[-1] == '\n')
break;
p += fieldlen;
}
/* Skip to the first column followed by a space */
p += fieldlen;
p = memchr(p, ':', bufend-p);
if (p == NULL || p[1] != ' ')
goto EXIT;
/* Find the end of the line */
p += 2;
q = memchr(p, '\n', bufend-p);
if (q == NULL)
q = bufend;
/* Copy the line into a heap-allocated buffer */
len = q-p;
result = malloc(len+1);
if (result == NULL)
goto EXIT;
memcpy(result, p, len);
result[len] = '\0';
EXIT:
return result;
}
/* Like strlen(), but for constant string literals */
#define STRLEN_CONST(x) ((sizeof(x)-1)
/* Checks that a space-separated list of items contains one given 'item'.
* Returns 1 if found, 0 otherwise.
*/
static int
has_list_item(const char* list, const char* item)
{
const char* p = list;
int itemlen = strlen(item);
if (list == NULL)
return 0;
while (*p) {
const char* q;
/* skip spaces */
while (*p == ' ' || *p == '\t')
p++;
/* find end of current list item */
q = p;
while (*q && *q != ' ' && *q != '\t')
q++;
if (itemlen == q-p && !memcmp(p, item, itemlen))
return 1;
/* skip to next item */
p = q;
}
return 0;
}
/* Parse an decimal integer starting from 'input', but not going further
* than 'limit'. Return the value into '*result'.
*
* NOTE: Does not skip over leading spaces, or deal with sign characters.
* NOTE: Ignores overflows.
*
* The function returns NULL in case of error (bad format), or the new
* position after the decimal number in case of success (which will always
* be <= 'limit').
*/
static const char*
parse_decimal(const char* input, const char* limit, int* result)
{
const char* p = input;
int val = 0;
while (p < limit) {
int d = (*p - '0');
if ((unsigned)d >= 10U)
break;
val = val*10 + d;
p++;
}
if (p == input)
return NULL;
*result = val;
return p;
}
/* This small data type is used to represent a CPU list / mask, as read
* from sysfs on Linux. See http://www.kernel.org/doc/Documentation/cputopology.txt
*
* For now, we don't expect more than 32 cores on mobile devices, so keep
* everything simple.
*/
typedef struct {
uint32_t mask;
} CpuList;
static __inline__ void
cpulist_init(CpuList* list) {
list->mask = 0;
}
static __inline__ void
cpulist_and(CpuList* list1, CpuList* list2) {
list1->mask &= list2->mask;
}
static __inline__ void
cpulist_set(CpuList* list, int index) {
if ((unsigned)index < 32) {
list->mask |= (uint32_t)(1U << index);
}
}
static __inline__ int
cpulist_count(CpuList* list) {
return __builtin_popcount(list->mask);
}
/* Parse a textual list of cpus and store the result inside a CpuList object.
* Input format is the following:
* - comma-separated list of items (no spaces)
* - each item is either a single decimal number (cpu index), or a range made
* of two numbers separated by a single dash (-). Ranges are inclusive.
*
* Examples: 0
* 2,4-127,128-143
* 0-1
*/
static void
cpulist_parse(CpuList* list, const char* line, int line_len)
{
const char* p = line;
const char* end = p + line_len;
const char* q;
/* NOTE: the input line coming from sysfs typically contains a
* trailing newline, so take care of it in the code below
*/
while (p < end && *p != '\n')
{
int val, start_value, end_value;
/* Find the end of current item, and put it into 'q' */
q = memchr(p, ',', end-p);
if (q == NULL) {
q = end;
}
/* Get first value */
p = parse_decimal(p, q, &start_value);
if (p == NULL)
goto BAD_FORMAT;
end_value = start_value;
/* If we're not at the end of the item, expect a dash and
* and integer; extract end value.
*/
if (p < q && *p == '-') {
p = parse_decimal(p+1, q, &end_value);
if (p == NULL)
goto BAD_FORMAT;
}
/* Set bits CPU list bits */
for (val = start_value; val <= end_value; val++) {
cpulist_set(list, val);
}
/* Jump to next item */
p = q;
if (p < end)
p++;
}
BAD_FORMAT:
;
}
/* Read a CPU list from one sysfs file */
static void
cpulist_read_from(CpuList* list, const char* filename)
{
char file[64];
int filelen;
cpulist_init(list);
filelen = read_file(filename, file, sizeof file);
if (filelen < 0) {
D("Could not read %s: %s\n", filename, strerror(errno));
return;
}
cpulist_parse(list, file, filelen);
}
// See <asm/hwcap.h> kernel header.
#define HWCAP_VFP (1 << 6)
#define HWCAP_IWMMXT (1 << 9)
#define HWCAP_NEON (1 << 12)
#define HWCAP_VFPv3 (1 << 13)
#define HWCAP_VFPv3D16 (1 << 14)
#define HWCAP_VFPv4 (1 << 16)
#define HWCAP_IDIVA (1 << 17)
#define HWCAP_IDIVT (1 << 18)
#define AT_HWCAP 16
#if defined(__arm__)
/* Compute the ELF HWCAP flags.
*/
static uint32_t
get_elf_hwcap(const char* cpuinfo, int cpuinfo_len)
{
/* IMPORTANT:
* Accessing /proc/self/auxv doesn't work anymore on all
* platform versions. More specifically, when running inside
* a regular application process, most of /proc/self/ will be
* non-readable, including /proc/self/auxv. This doesn't
* happen however if the application is debuggable, or when
* running under the "shell" UID, which is why this was not
* detected appropriately.
*/
#if 0
uint32_t result = 0;
const char filepath[] = "/proc/self/auxv";
int fd = open(filepath, O_RDONLY);
if (fd < 0) {
D("Could not open %s: %s\n", filepath, strerror(errno));
return 0;
}
struct { uint32_t tag; uint32_t value; } entry;
for (;;) {
int ret = read(fd, (char*)&entry, sizeof entry);
if (ret < 0) {
if (errno == EINTR)
continue;
D("Error while reading %s: %s\n", filepath, strerror(errno));
break;
}
// Detect end of list.
if (ret == 0 || (entry.tag == 0 && entry.value == 0))
break;
if (entry.tag == AT_HWCAP) {
result = entry.value;
break;
}
}
close(fd);
return result;
#else
// Recreate ELF hwcaps by parsing /proc/cpuinfo Features tag.
uint32_t hwcaps = 0;
char* cpuFeatures = extract_cpuinfo_field(cpuinfo, cpuinfo_len, "Features");
if (cpuFeatures != NULL) {
D("Found cpuFeatures = '%s'\n", cpuFeatures);
if (has_list_item(cpuFeatures, "vfp"))
hwcaps |= HWCAP_VFP;
if (has_list_item(cpuFeatures, "vfpv3"))
hwcaps |= HWCAP_VFPv3;
if (has_list_item(cpuFeatures, "vfpv3d16"))
hwcaps |= HWCAP_VFPv3D16;
if (has_list_item(cpuFeatures, "vfpv4"))
hwcaps |= HWCAP_VFPv4;
if (has_list_item(cpuFeatures, "neon"))
hwcaps |= HWCAP_NEON;
if (has_list_item(cpuFeatures, "idiva"))
hwcaps |= HWCAP_IDIVA;
if (has_list_item(cpuFeatures, "idivt"))
hwcaps |= HWCAP_IDIVT;
if (has_list_item(cpuFeatures, "idiv"))
hwcaps |= HWCAP_IDIVA | HWCAP_IDIVT;
if (has_list_item(cpuFeatures, "iwmmxt"))
hwcaps |= HWCAP_IWMMXT;
free(cpuFeatures);
}
return hwcaps;
#endif
}
#endif /* __arm__ */
/* Return the number of cpus present on a given device.
*
* To handle all weird kernel configurations, we need to compute the
* intersection of the 'present' and 'possible' CPU lists and count
* the result.
*/
static int
get_cpu_count(void)
{
CpuList cpus_present[1];
CpuList cpus_possible[1];
cpulist_read_from(cpus_present, "/sys/devices/system/cpu/present");
cpulist_read_from(cpus_possible, "/sys/devices/system/cpu/possible");
/* Compute the intersection of both sets to get the actual number of
* CPU cores that can be used on this device by the kernel.
*/
cpulist_and(cpus_present, cpus_possible);
return cpulist_count(cpus_present);
}
static void
android_cpuInitFamily(void)
{
#if defined(__ARM_ARCH__)
g_cpuFamily = ANDROID_CPU_FAMILY_ARM;
#elif defined(__i386__)
g_cpuFamily = ANDROID_CPU_FAMILY_X86;
#elif defined(_MIPS_ARCH)
g_cpuFamily = ANDROID_CPU_FAMILY_MIPS;
#else
g_cpuFamily = ANDROID_CPU_FAMILY_UNKNOWN;
#endif
}
static void
android_cpuInit(void)
{
char* cpuinfo = NULL;
int cpuinfo_len;
android_cpuInitFamily();
g_cpuFeatures = 0;
g_cpuCount = 1;
g_inited = 1;
cpuinfo_len = get_file_size("/proc/cpuinfo");
if (cpuinfo_len < 0) {
D("cpuinfo_len cannot be computed!");
return;
}
cpuinfo = malloc(cpuinfo_len);
if (cpuinfo == NULL) {
D("cpuinfo buffer could not be allocated");
return;
}
cpuinfo_len = read_file("/proc/cpuinfo", cpuinfo, cpuinfo_len);
D("cpuinfo_len is (%d):\n%.*s\n", cpuinfo_len,
cpuinfo_len >= 0 ? cpuinfo_len : 0, cpuinfo);
if (cpuinfo_len < 0) /* should not happen */ {
free(cpuinfo);
return;
}
/* Count the CPU cores, the value may be 0 for single-core CPUs */
g_cpuCount = get_cpu_count();
if (g_cpuCount == 0) {
g_cpuCount = 1;
}
D("found cpuCount = %d\n", g_cpuCount);
#ifdef __ARM_ARCH__
{
char* features = NULL;
char* architecture = NULL;
/* Extract architecture from the "CPU Architecture" field.
* The list is well-known, unlike the the output of
* the 'Processor' field which can vary greatly.
*
* See the definition of the 'proc_arch' array in
* $KERNEL/arch/arm/kernel/setup.c and the 'c_show' function in
* same file.
*/
char* cpuArch = extract_cpuinfo_field(cpuinfo, cpuinfo_len, "CPU architecture");
if (cpuArch != NULL) {
char* end;
long archNumber;
int hasARMv7 = 0;
D("found cpuArch = '%s'\n", cpuArch);
/* read the initial decimal number, ignore the rest */
archNumber = strtol(cpuArch, &end, 10);
/* Here we assume that ARMv8 will be upwards compatible with v7
* in the future. Unfortunately, there is no 'Features' field to
* indicate that Thumb-2 is supported.
*/
if (end > cpuArch && archNumber >= 7) {
hasARMv7 = 1;
}
/* Unfortunately, it seems that certain ARMv6-based CPUs
* report an incorrect architecture number of 7!
*
* See http://code.google.com/p/android/issues/detail?id=10812
*
* We try to correct this by looking at the 'elf_format'
* field reported by the 'Processor' field, which is of the
* form of "(v7l)" for an ARMv7-based CPU, and "(v6l)" for
* an ARMv6-one.
*/
if (hasARMv7) {
char* cpuProc = extract_cpuinfo_field(cpuinfo, cpuinfo_len,
"Processor");
if (cpuProc != NULL) {
D("found cpuProc = '%s'\n", cpuProc);
if (has_list_item(cpuProc, "(v6l)")) {
D("CPU processor and architecture mismatch!!\n");
hasARMv7 = 0;
}
free(cpuProc);
}
}
if (hasARMv7) {
g_cpuFeatures |= ANDROID_CPU_ARM_FEATURE_ARMv7;
}
/* The LDREX / STREX instructions are available from ARMv6 */
if (archNumber >= 6) {
g_cpuFeatures |= ANDROID_CPU_ARM_FEATURE_LDREX_STREX;
}
free(cpuArch);
}
/* Extract the list of CPU features from ELF hwcaps */
uint32_t hwcaps = get_elf_hwcap(cpuinfo, cpuinfo_len);
if (hwcaps != 0) {
int has_vfp = (hwcaps & HWCAP_VFP);
int has_vfpv3 = (hwcaps & HWCAP_VFPv3);
int has_vfpv3d16 = (hwcaps & HWCAP_VFPv3D16);
int has_vfpv4 = (hwcaps & HWCAP_VFPv4);
int has_neon = (hwcaps & HWCAP_NEON);
int has_idiva = (hwcaps & HWCAP_IDIVA);
int has_idivt = (hwcaps & HWCAP_IDIVT);
int has_iwmmxt = (hwcaps & HWCAP_IWMMXT);
// The kernel does a poor job at ensuring consistency when
// describing CPU features. So lots of guessing is needed.
// 'vfpv4' implies VFPv3|VFP_FMA|FP16
if (has_vfpv4)
g_cpuFeatures |= ANDROID_CPU_ARM_FEATURE_VFPv3 |
ANDROID_CPU_ARM_FEATURE_VFP_FP16 |
ANDROID_CPU_ARM_FEATURE_VFP_FMA;
// 'vfpv3' or 'vfpv3d16' imply VFPv3. Note that unlike GCC,
// a value of 'vfpv3' doesn't necessarily mean that the D32
// feature is present, so be conservative. All CPUs in the
// field that support D32 also support NEON, so this should
// not be a problem in practice.
if (has_vfpv3 || has_vfpv3d16)
g_cpuFeatures |= ANDROID_CPU_ARM_FEATURE_VFPv3;
// 'vfp' is super ambiguous. Depending on the kernel, it can
// either mean VFPv2 or VFPv3. Make it depend on ARMv7.
if (has_vfp) {
if (g_cpuFeatures & ANDROID_CPU_ARM_FEATURE_ARMv7)
g_cpuFeatures |= ANDROID_CPU_ARM_FEATURE_VFPv3;
else
g_cpuFeatures |= ANDROID_CPU_ARM_FEATURE_VFPv2;
}
// Neon implies VFPv3|D32, and if vfpv4 is detected, NEON_FMA
if (has_neon) {
g_cpuFeatures |= ANDROID_CPU_ARM_FEATURE_VFPv3 |
ANDROID_CPU_ARM_FEATURE_NEON |
ANDROID_CPU_ARM_FEATURE_VFP_D32;
if (has_vfpv4)
g_cpuFeatures |= ANDROID_CPU_ARM_FEATURE_NEON_FMA;
}
// VFPv3 implies VFPv2 and ARMv7
if (g_cpuFeatures & ANDROID_CPU_ARM_FEATURE_VFPv3)
g_cpuFeatures |= ANDROID_CPU_ARM_FEATURE_VFPv2 |
ANDROID_CPU_ARM_FEATURE_ARMv7;
// Note that some buggy kernels do not report these even when
// the CPU actually support the division instructions. However,
// assume that if 'vfpv4' is detected, then the CPU supports
// sdiv/udiv properly.
if (has_idiva || has_vfpv4)
g_cpuFeatures |= ANDROID_CPU_ARM_FEATURE_IDIV_ARM;
if (has_idivt || has_vfpv4)
g_cpuFeatures |= ANDROID_CPU_ARM_FEATURE_IDIV_THUMB2;
if (has_iwmmxt)
g_cpuFeatures |= ANDROID_CPU_ARM_FEATURE_iWMMXt;
}
}
#endif /* __ARM_ARCH__ */
#ifdef __i386__
int regs[4];
/* According to http://en.wikipedia.org/wiki/CPUID */
#define VENDOR_INTEL_b 0x756e6547
#define VENDOR_INTEL_c 0x6c65746e
#define VENDOR_INTEL_d 0x49656e69
x86_cpuid(0, regs);
int vendorIsIntel = (regs[1] == VENDOR_INTEL_b &&
regs[2] == VENDOR_INTEL_c &&
regs[3] == VENDOR_INTEL_d);
x86_cpuid(1, regs);
if ((regs[2] & (1 << 9)) != 0) {
g_cpuFeatures |= ANDROID_CPU_X86_FEATURE_SSSE3;
}
if ((regs[2] & (1 << 23)) != 0) {
g_cpuFeatures |= ANDROID_CPU_X86_FEATURE_POPCNT;
}
if (vendorIsIntel && (regs[2] & (1 << 22)) != 0) {
g_cpuFeatures |= ANDROID_CPU_X86_FEATURE_MOVBE;
}
#endif
free(cpuinfo);
}
AndroidCpuFamily
android_getCpuFamily(void)
{
pthread_once(&g_once, android_cpuInit);
return g_cpuFamily;
}
uint64_t
android_getCpuFeatures(void)
{
pthread_once(&g_once, android_cpuInit);
return g_cpuFeatures;
}
int
android_getCpuCount(void)
{
pthread_once(&g_once, android_cpuInit);
return g_cpuCount;
}
static void
android_cpuInitDummy(void)
{
g_inited = 1;
}
int
android_setCpu(int cpu_count, uint64_t cpu_features)
{
/* Fail if the library was already initialized. */
if (g_inited)
return 0;
android_cpuInitFamily();
g_cpuCount = (cpu_count <= 0 ? 1 : cpu_count);
g_cpuFeatures = cpu_features;
pthread_once(&g_once, android_cpuInitDummy);
return 1;
}
/*
* Technical note: Making sense of ARM's FPU architecture versions.
*
* FPA was ARM's first attempt at an FPU architecture. There is no Android
* device that actually uses it since this technology was already obsolete
* when the project started. If you see references to FPA instructions
* somewhere, you can be sure that this doesn't apply to Android at all.
*
* FPA was followed by "VFP", soon renamed "VFPv1" due to the emergence of
* new versions / additions to it. ARM considers this obsolete right now,
* and no known Android device implements it either.
*
* VFPv2 added a few instructions to VFPv1, and is an *optional* extension
* supported by some ARMv5TE, ARMv6 and ARMv6T2 CPUs. Note that a device
* supporting the 'armeabi' ABI doesn't necessarily support these.
*
* VFPv3-D16 adds a few instructions on top of VFPv2 and is typically used
* on ARMv7-A CPUs which implement a FPU. Note that it is also mandated
* by the Android 'armeabi-v7a' ABI. The -D16 suffix in its name means
* that it provides 16 double-precision FPU registers (d0-d15) and 32
* single-precision ones (s0-s31) which happen to be mapped to the same
* register banks.
*
* VFPv3-D32 is the name of an extension to VFPv3-D16 that provides 16
* additional double precision registers (d16-d31). Note that there are
* still only 32 single precision registers.
*
* VFPv3xD is a *subset* of VFPv3-D16 that only provides single-precision
* registers. It is only used on ARMv7-M (i.e. on micro-controllers) which
* are not supported by Android. Note that it is not compatible with VFPv2.
*
* NOTE: The term 'VFPv3' usually designate either VFPv3-D16 or VFPv3-D32
* depending on context. For example GCC uses it for VFPv3-D32, but
* the Linux kernel code uses it for VFPv3-D16 (especially in
* /proc/cpuinfo). Always try to use the full designation when
* possible.
*
* NEON, a.k.a. "ARM Advanced SIMD" is an extension that provides
* instructions to perform parallel computations on vectors of 8, 16,
* 32, 64 and 128 bit quantities. NEON requires VFPv32-D32 since all
* NEON registers are also mapped to the same register banks.
*
* VFPv4-D16, adds a few instructions on top of VFPv3-D16 in order to
* perform fused multiply-accumulate on VFP registers, as well as
* half-precision (16-bit) conversion operations.
*
* VFPv4-D32 is VFPv4-D16 with 32, instead of 16, FPU double precision
* registers.
*
* VPFv4-NEON is VFPv4-D32 with NEON instructions. It also adds fused
* multiply-accumulate instructions that work on the NEON registers.
*
* NOTE: Similarly, "VFPv4" might either reference VFPv4-D16 or VFPv4-D32
* depending on context.
*
* The following information was determined by scanning the binutils-2.22
* sources:
*
* Basic VFP instruction subsets:
*
* #define FPU_VFP_EXT_V1xD 0x08000000 // Base VFP instruction set.
* #define FPU_VFP_EXT_V1 0x04000000 // Double-precision insns.
* #define FPU_VFP_EXT_V2 0x02000000 // ARM10E VFPr1.
* #define FPU_VFP_EXT_V3xD 0x01000000 // VFPv3 single-precision.
* #define FPU_VFP_EXT_V3 0x00800000 // VFPv3 double-precision.
* #define FPU_NEON_EXT_V1 0x00400000 // Neon (SIMD) insns.
* #define FPU_VFP_EXT_D32 0x00200000 // Registers D16-D31.
* #define FPU_VFP_EXT_FP16 0x00100000 // Half-precision extensions.
* #define FPU_NEON_EXT_FMA 0x00080000 // Neon fused multiply-add
* #define FPU_VFP_EXT_FMA 0x00040000 // VFP fused multiply-add
*
* FPU types (excluding NEON)
*
* FPU_VFP_V1xD (EXT_V1xD)
* |
* +--------------------------+
* | |
* FPU_VFP_V1 (+EXT_V1) FPU_VFP_V3xD (+EXT_V2+EXT_V3xD)
* | |
* | |
* FPU_VFP_V2 (+EXT_V2) FPU_VFP_V4_SP_D16 (+EXT_FP16+EXT_FMA)
* |
* FPU_VFP_V3D16 (+EXT_Vx3D+EXT_V3)
* |
* +--------------------------+
* | |
* FPU_VFP_V3 (+EXT_D32) FPU_VFP_V4D16 (+EXT_FP16+EXT_FMA)
* | |
* | FPU_VFP_V4 (+EXT_D32)
* |
* FPU_VFP_HARD (+EXT_FMA+NEON_EXT_FMA)
*
* VFP architectures:
*
* ARCH_VFP_V1xD (EXT_V1xD)
* |
* +------------------+
* | |
* | ARCH_VFP_V3xD (+EXT_V2+EXT_V3xD)
* | |
* | ARCH_VFP_V3xD_FP16 (+EXT_FP16)
* | |
* | ARCH_VFP_V4_SP_D16 (+EXT_FMA)
* |
* ARCH_VFP_V1 (+EXT_V1)
* |
* ARCH_VFP_V2 (+EXT_V2)
* |
* ARCH_VFP_V3D16 (+EXT_V3xD+EXT_V3)
* |
* +-------------------+
* | |
* | ARCH_VFP_V3D16_FP16 (+EXT_FP16)
* |
* +-------------------+
* | |
* | ARCH_VFP_V4_D16 (+EXT_FP16+EXT_FMA)
* | |
* | ARCH_VFP_V4 (+EXT_D32)
* | |
* | ARCH_NEON_VFP_V4 (+EXT_NEON+EXT_NEON_FMA)
* |
* ARCH_VFP_V3 (+EXT_D32)
* |
* +-------------------+
* | |
* | ARCH_VFP_V3_FP16 (+EXT_FP16)
* |
* ARCH_VFP_V3_PLUS_NEON_V1 (+EXT_NEON)
* |
* ARCH_NEON_FP16 (+EXT_FP16)
*
* -fpu=<name> values and their correspondance with FPU architectures above:
*
* {"vfp", FPU_ARCH_VFP_V2},
* {"vfp9", FPU_ARCH_VFP_V2},
* {"vfp3", FPU_ARCH_VFP_V3}, // For backwards compatbility.
* {"vfp10", FPU_ARCH_VFP_V2},
* {"vfp10-r0", FPU_ARCH_VFP_V1},
* {"vfpxd", FPU_ARCH_VFP_V1xD},
* {"vfpv2", FPU_ARCH_VFP_V2},
* {"vfpv3", FPU_ARCH_VFP_V3},
* {"vfpv3-fp16", FPU_ARCH_VFP_V3_FP16},
* {"vfpv3-d16", FPU_ARCH_VFP_V3D16},
* {"vfpv3-d16-fp16", FPU_ARCH_VFP_V3D16_FP16},
* {"vfpv3xd", FPU_ARCH_VFP_V3xD},
* {"vfpv3xd-fp16", FPU_ARCH_VFP_V3xD_FP16},
* {"neon", FPU_ARCH_VFP_V3_PLUS_NEON_V1},
* {"neon-fp16", FPU_ARCH_NEON_FP16},
* {"vfpv4", FPU_ARCH_VFP_V4},
* {"vfpv4-d16", FPU_ARCH_VFP_V4D16},
* {"fpv4-sp-d16", FPU_ARCH_VFP_V4_SP_D16},
* {"neon-vfpv4", FPU_ARCH_NEON_VFP_V4},
*
*
* Simplified diagram that only includes FPUs supported by Android:
* Only ARCH_VFP_V3D16 is actually mandated by the armeabi-v7a ABI,
* all others are optional and must be probed at runtime.
*
* ARCH_VFP_V3D16 (EXT_V1xD+EXT_V1+EXT_V2+EXT_V3xD+EXT_V3)
* |
* +-------------------+
* | |
* | ARCH_VFP_V3D16_FP16 (+EXT_FP16)
* |
* +-------------------+
* | |
* | ARCH_VFP_V4_D16 (+EXT_FP16+EXT_FMA)
* | |
* | ARCH_VFP_V4 (+EXT_D32)
* | |
* | ARCH_NEON_VFP_V4 (+EXT_NEON+EXT_NEON_FMA)
* |
* ARCH_VFP_V3 (+EXT_D32)
* |
* +-------------------+
* | |
* | ARCH_VFP_V3_FP16 (+EXT_FP16)
* |
* ARCH_VFP_V3_PLUS_NEON_V1 (+EXT_NEON)
* |
* ARCH_NEON_FP16 (+EXT_FP16)
*
*/