From 4f7784cd1e8882d60955cfd4549949e10a83c779 Mon Sep 17 00:00:00 2001
From: Jack Lloyd <jack@randombit.net>
Date: Sun, 11 Jan 2026 08:14:05 -0500
Subject: [PATCH] Add a BOTAN_FN_ISA flag for CPU RNG function

This seems to be needed for ARMv8.5 RNG support (#5228)
---
 src/lib/rng/processor_rng/info.txt          | 6 ------
 src/lib/rng/processor_rng/processor_rng.cpp | 3 ++-
 src/lib/utils/isa_extn.h                    | 2 ++
 3 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/src/lib/rng/processor_rng/info.txt b/src/lib/rng/processor_rng/info.txt
index 3429af09577..eb2d5ef51b8 100644
--- a/src/lib/rng/processor_rng/info.txt
+++ b/src/lib/rng/processor_rng/info.txt
@@ -17,12 +17,6 @@ ppc64
 processor_rng.h
 </header:public>
 
-<isa>
-x86_32:rdrand
-x86_64:rdrand
-ppc64:power9
-</isa>
-
 <requires>
 cpuid
 </requires>
diff --git a/src/lib/rng/processor_rng/processor_rng.cpp b/src/lib/rng/processor_rng/processor_rng.cpp
index 4711e1f12fc..31557543fa8 100644
--- a/src/lib/rng/processor_rng/processor_rng.cpp
+++ b/src/lib/rng/processor_rng/processor_rng.cpp
@@ -7,6 +7,7 @@
 #include <botan/processor_rng.h>
 
 #include <botan/internal/cpuid.h>
+#include <botan/internal/isa_extn.h>
 #include <botan/internal/loadstor.h>
 #include <botan/internal/target_info.h>
 
@@ -48,7 +49,7 @@ typedef uint32_t hwrng_output;
 typedef uint64_t hwrng_output;
 #endif
 
-hwrng_output read_hwrng(bool& success) {
+hwrng_output BOTAN_FN_ISA_RNG read_hwrng(bool& success) {
    hwrng_output output = 0;  // NOLINT(*-const-correctness) clang-tidy doesn't understand inline asm
    success = false;
 
diff --git a/src/lib/utils/isa_extn.h b/src/lib/utils/isa_extn.h
index 667e71e8421..e78564fa70a 100644
--- a/src/lib/utils/isa_extn.h
+++ b/src/lib/utils/isa_extn.h
@@ -28,6 +28,7 @@
    #define BOTAN_FN_ISA_SHANI BOTAN_FUNC_ISA("sha,ssse3,sse4.1")
    #define BOTAN_FN_ISA_SHA512 BOTAN_FUNC_ISA("sha512,avx2")
    #define BOTAN_FN_ISA_BMI2 BOTAN_FUNC_ISA("bmi,bmi2")
+   #define BOTAN_FN_ISA_RNG BOTAN_FUNC_ISA("rdrnd")
    #define BOTAN_FN_ISA_SSE2 BOTAN_FUNC_ISA("sse2")
    #define BOTAN_FN_ISA_AVX2 BOTAN_FUNC_ISA("avx2")
    #define BOTAN_FN_ISA_AVX2_BMI2 BOTAN_FUNC_ISA("avx2,bmi,bmi2")
@@ -64,6 +65,7 @@
    #define BOTAN_FN_ISA_SIMD_4X32 BOTAN_FUNC_ISA("altivec")
    #define BOTAN_FN_ISA_CLMUL BOTAN_FUNC_ISA("vsx,crypto")
    #define BOTAN_FN_ISA_AES BOTAN_FUNC_ISA("vsx,crypto")
+   #define BOTAN_FN_ISA_RNG BOTAN_FUNC_ISA("cpu=power9")
 
 #endif