From de79154a58dac7d81f3ba75c50ec25ad00557af7 Mon Sep 17 00:00:00 2001
From: Brad Smith <brad@comstyle.com>
Date: Sat, 12 Sep 2026 19:33:46 -0400
Subject: [PATCH] Add CPU detection for FreeBSD / OpenBSD AArch64

---
 absl/base/config.h               |  9 +++++++++
 absl/base/internal/cpu_detect.cc | 24 ++++++++++++++++++++----
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/absl/base/config.h b/absl/base/config.h
index e3e2c96a39c..f4926e59e9f 100644
--- a/absl/base/config.h
+++ b/absl/base/config.h
@@ -381,6 +381,15 @@ static_assert(ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 #define ABSL_HAVE_SCHED_YIELD 1
 #endif
 
+// ABSL_HAVE_ELF_AUX_INFO
+//
+// Checks whether the platform implements elf_aux_info(3).
+#ifdef ABSL_HAVE_ELF_AUX_INFO
+#error ABSL_HAVE_ELF_AUX_INFO cannot be directly set
+#elif (defined(__FreeBSD__) || defined(__OpenBSD__)) && __has_include(<sys/auxv.h>)
+#define ABSL_HAVE_ELF_AUX_INFO 1
+#endif
+
 // ABSL_HAVE_SEMAPHORE_H
 //
 // Checks whether the platform supports the <semaphore.h> header and sem_init(3)
diff --git a/absl/base/internal/cpu_detect.cc b/absl/base/internal/cpu_detect.cc
index 4ceed84a0c7..1fbedfabaff 100644
--- a/absl/base/internal/cpu_detect.cc
+++ b/absl/base/internal/cpu_detect.cc
@@ -20,8 +20,11 @@
 
 #include "absl/base/config.h"
 
-#if defined(__aarch64__) && defined(__linux__)
+#if defined(__aarch64__) && \
+    (defined(__linux__) || defined(ABSL_HAVE_ELF_AUX_INFO))
+#if defined(__linux__)
 #include <asm/hwcap.h>
+#endif
 #include <sys/auxv.h>
 #endif
 
@@ -265,7 +268,8 @@ bool SupportsBmi2() {
   return (cpu_info[1] & (1 << 8)) != 0;
 }
 
-#elif defined(__aarch64__) && defined(__linux__)
+#elif defined(__aarch64__) && \
+    (defined(__linux__) || defined(ABSL_HAVE_ELF_AUX_INFO))
 
 #ifndef HWCAP_CPUID
 #define HWCAP_CPUID (1 << 11)
@@ -276,12 +280,18 @@ bool SupportsBmi2() {
 
 CpuType GetCpuType() {
   // MIDR_EL1 is not visible to EL0, however the access will be emulated by
-  // linux if AT_HWCAP has HWCAP_CPUID set.
+  // Linux, FreeBSD and OpenBSD if AT_HWCAP has HWCAP_CPUID set.
   //
   // This method will be unreliable on heterogeneous computing systems (ex:
   // big.LITTLE) since the value of MIDR_EL1 will change based on the calling
   // thread.
+#if defined(ABSL_HAVE_ELF_AUX_INFO)
+  uint64_t hwcaps;
+  if (elf_aux_info(AT_HWCAP, &hwcaps, sizeof(hwcaps)) != 0)
+    return CpuType::kUnknown;
+#else
   uint64_t hwcaps = getauxval(AT_HWCAP);
+#endif
   if (hwcaps & HWCAP_CPUID) {
     uint64_t midr = 0;
     ABSL_INTERNAL_AARCH64_ID_REG_READ(MIDR_EL1, midr);
@@ -328,7 +338,13 @@ CpuType GetCpuType() {
 }
 
 bool SupportsArmCRC32PMULL() {
-#if defined(HWCAP_CRC32) && defined(HWCAP_PMULL)
+#if defined(ABSL_HAVE_ELF_AUX_INFO)
+  uint64_t hwcaps;
+  bool ret = false;
+  if (elf_aux_info(AT_HWCAP, &hwcaps, sizeof(hwcaps)) == 0)
+    ret = (hwcaps & HWCAP_CRC32) && (hwcaps & HWCAP_PMULL);
+  return ret;
+#elif defined(HWCAP_CRC32) && defined(HWCAP_PMULL)
   uint64_t hwcaps = getauxval(AT_HWCAP);
   return (hwcaps & HWCAP_CRC32) && (hwcaps & HWCAP_PMULL);
 #else