feat: enable CPU runtime dispatch (GGML_CPU_ALL_VARIANTS)

Signed-off-by: Onuralp SEZER <thunderbirdtr@fedoraproject.org>

0001-Load-the-dynamic-backends-from-the-library-itself.patch

@@ -0,0 +1,48 @@
+From: Onuralp Sezer <thunderbirdtr@fedoraproject.org>
+Date: Sun, 23 Aug 2026 15:10:00 +0300
+Subject: [PATCH] Load the dynamic backends from the library itself
+
+When whisper.cpp is built with GGML_BACKEND_DL the compute backends become
+loadable modules, and something has to call ggml_backend_load_all() before any
+device can be found. Today only the bundled example programs do that, so a
+program that links libwhisper and calls whisper_init_* directly finds no
+devices at all and ggml aborts on GGML_ASSERT(device).
+
+Do it inside whisper_backend_init_gpu, guarded by std::call_once so repeated
+context creation stays cheap. It is a no-op for a build that is not using
+loadable backends.
+
+Signed-off-by: Onuralp Sezer <thunderbirdtr@fedoraproject.org>
+---
+ src/whisper.cpp | 11 +++++++++++
+ 1 file changed, 11 insertions(+)
+
+diff --git a/src/whisper.cpp b/src/whisper.cpp
+index 1111111..2222222 100644
+--- a/src/whisper.cpp
++++ b/src/whisper.cpp
+@@ -28,6 +28,7 @@
+ #include <fstream>
+ #include <functional>
+ #include <map>
++#include <mutex>
+ #include <random>
+ #include <regex>
+ #include <set>
+@@ -1290,6 +1291,16 @@ static size_t whisper_backend_buffer_size(const whisper_context_params & params)
+ static ggml_backend_t whisper_backend_init_gpu(const whisper_context_params & params) {
+     ggml_log_set(g_state.log_callback, g_state.log_callback_user_data);
+ 
++    // With GGML_BACKEND_DL the backends are loadable modules and nothing has
++    // registered them yet. Callers that link this library rather than using the
++    // bundled examples would otherwise find no devices at all.
++    {
++        static std::once_flag flag;
++        std::call_once(flag, [] {
++            ggml_backend_load_all();
++        });
++    }
++
+     ggml_backend_dev_t dev = nullptr;
+ 
+     int cnt = 0;

whisper-cpp.spec

@@ -14,6 +14,11 @@ Release:        %autorelease
 URL:            https://github.com/ggerganov/whisper.cpp
 Source0:        %{url}/archive/refs/tags/v%{version}.tar.gz#/whisper.cpp-%{version}.tar.gz
 
+# A library built with GGML_BACKEND_DL has to register its own backends, or
+# anything linking it finds no devices and aborts. Drop this once ggml does
+# the registration itself.
+Patch0:         0001-Load-the-dynamic-backends-from-the-library-itself.patch
+
 ExclusiveArch:  x86_64 aarch64 ppc64le
 %global toolchain gcc
 
@@ -43,6 +48,17 @@ ExclusiveArch:  x86_64 aarch64 ppc64le
 %global rocm_gpu_list %{nil}
 %endif
 
+# GGML_CPU_ALL_VARIANTS builds one CPU backend per microarchitecture and picks
+# the best one at startup, so we keep running on old hardware while still using
+# AVX2 and friends where they exist. Upstream supports it on x86, ARM and
+# PowerPC, which is every arch in ExclusiveArch above.
+#
+# The backends become dlopened modules, and they are only looked for in this
+# directory, the executable's directory and the current one. Without
+# GGML_BACKEND_DIR they would land in %%{_bindir} and never be found. Keep it
+# package private, llama-cpp ships its own copy of ggml.
+%global backend_dir %{_libdir}/%{name}
+
 %bcond_with test
 %if %{with test}
 %global build_test ON
@@ -118,6 +134,9 @@ recognition (ASR) model:
     -DWHISPER_OPENVINO=%{build_openvino} \
     -DGGML_HIP=%{build_rocm} \
     -DGGML_NATIVE=OFF \
+    -DGGML_BACKEND_DL=ON \
+    -DGGML_CPU_ALL_VARIANTS=ON \
+    -DGGML_BACKEND_DIR=%{backend_dir} \
     -DGGML_AMX_TILE=OFF \
     -DGGML_AMX_INT8=OFF \
     -DGGML_AMX_BF16=OFF \
@@ -156,20 +175,18 @@ find %{buildroot} -name 'whisper.pc' -delete
 %license LICENSE
 %{_libdir}/libggml.so.*
 %{_libdir}/libggml-base.so.*
-%{_libdir}/libggml-cpu.so.*
 %{_libdir}/libwhisper.so.*
 %{_libdir}/libparakeet.so.*
 
-%if %{with rocm}
-%{_libdir}/libggml-hip.so.*
-%endif
+# The backend modules carry no version, but they are dlopened at runtime, so
+# they belong here and not in the devel package.
+%{backend_dir}/
 
 %files devel
 %doc README.md
 %{_includedir}/*.h
 %{_libdir}/libggml.so
 %{_libdir}/libggml-base.so
-%{_libdir}/libggml-cpu.so
 %{_libdir}/libparakeet.so
 %{_libdir}/libwhisper.so
 %{_libdir}/cmake/ggml/
@@ -177,10 +194,6 @@ find %{buildroot} -name 'whisper.pc' -delete
 %{_libdir}/cmake/whisper/
 %{_libdir}/pkgconfig/parakeet.pc
 
-%if %{with rocm}
-%{_libdir}/libggml-hip.so
-%endif
-
 %changelog
 %autochangelog