riscv64: pass a pointer to __riscv_hwprobe() to ifunc resolvers.

This way, callees don't need to worry about whether or not their
reference to __riscv_hwprobe() has been resolved before their ifunc
resolver is called.

This matches the current glibc proposal from rivos.

Test: treehugger
Change-Id: I0d5244aa837d0d1f0e6bd7d22091dfedb8a55bdb
diff --git a/libc/bionic/bionic_call_ifunc_resolver.cpp b/libc/bionic/bionic_call_ifunc_resolver.cpp
index 0b12088..d5a812c 100644
--- a/libc/bionic/bionic_call_ifunc_resolver.cpp
+++ b/libc/bionic/bionic_call_ifunc_resolver.cpp
@@ -28,6 +28,7 @@
 
 #include "private/bionic_call_ifunc_resolver.h"
 #include <sys/auxv.h>
+#include <sys/hwprobe.h>
 #include <sys/ifunc.h>
 
 #include "bionic/macros.h"
@@ -51,20 +52,15 @@
   return reinterpret_cast<ifunc_resolver_t>(resolver_addr)(arg._hwcap | _IFUNC_ARG_HWCAP, &arg);
 #elif defined(__arm__)
   typedef ElfW(Addr) (*ifunc_resolver_t)(unsigned long);
-  static unsigned long hwcap;
-  static bool initialized = false;
-  if (!initialized) {
-    initialized = true;
-    hwcap = getauxval(AT_HWCAP);
-  }
+  static unsigned long hwcap = getauxval(AT_HWCAP);
   return reinterpret_cast<ifunc_resolver_t>(resolver_addr)(hwcap);
 #elif defined(__riscv)
-  // The pointer argument is currently unused, but reserved for future
+  // The third argument is currently unused, but reserved for future
   // expansion. If we pass nullptr from the beginning, it'll be easier
   // to recognize if/when we pass actual data (and matches glibc).
-  typedef ElfW(Addr) (*ifunc_resolver_t)(uint64_t, void*);
+  typedef ElfW(Addr) (*ifunc_resolver_t)(uint64_t, __riscv_hwprobe_t, void*);
   static uint64_t hwcap = getauxval(AT_HWCAP);
-  return reinterpret_cast<ifunc_resolver_t>(resolver_addr)(hwcap, nullptr);
+  return reinterpret_cast<ifunc_resolver_t>(resolver_addr)(hwcap, __riscv_hwprobe, nullptr);
 #else
   typedef ElfW(Addr) (*ifunc_resolver_t)(void);
   return reinterpret_cast<ifunc_resolver_t>(resolver_addr)();
diff --git a/libc/include/sys/hwprobe.h b/libc/include/sys/hwprobe.h
index b1a8400..8e69e8a 100644
--- a/libc/include/sys/hwprobe.h
+++ b/libc/include/sys/hwprobe.h
@@ -53,6 +53,14 @@
  */
 int __riscv_hwprobe(struct riscv_hwprobe* _Nonnull __pairs, size_t __pair_count, size_t __cpu_count, unsigned long* _Nullable __cpus, unsigned __flags);
 
+/**
+ * The type of the second argument passed to riscv64 ifunc resolvers.
+ * This argument allows riscv64 ifunc resolvers to call __riscv_hwprobe()
+ * without worrying about whether that relocation is resolved before
+ * the ifunc resolver is called.
+ */
+typedef int (*__riscv_hwprobe_t)(struct riscv_hwprobe* _Nonnull __pairs, size_t __pair_count, size_t __cpu_count, unsigned long* _Nullable __cpus, unsigned __flags);
+
 __END_DECLS
 
 #endif
diff --git a/tests/ifunc_test.cpp b/tests/ifunc_test.cpp
index 1fdbf1a..09d987d 100644
--- a/tests/ifunc_test.cpp
+++ b/tests/ifunc_test.cpp
@@ -65,18 +65,18 @@
 #include <sys/hwprobe.h>
 
 static uint64_t g_hwcap;
+static __riscv_hwprobe_t g_hwprobe_ptr;
+static void* g_null;
 
 static riscv_hwprobe g_hwprobes[] = {{.key = RISCV_HWPROBE_KEY_IMA_EXT_0}};
 
-extern "C" fn_ptr_t hwcap_resolver(uint64_t hwcap, void* null) {
-  // Check hwcap like arm32/arm64.
+extern "C" fn_ptr_t hwcap_resolver(uint64_t hwcap, __riscv_hwprobe_t hwprobe_ptr, void* null) {
   g_hwcap = hwcap;
-
-  // For now, the pointer argument is reserved for future expansion.
-  if (null != NULL) abort();
+  g_hwprobe_ptr = hwprobe_ptr;
+  g_null = null;
 
   // Ensure that __riscv_hwprobe() can be called from an ifunc.
-  if (__riscv_hwprobe(g_hwprobes, 1, 0, nullptr, 0) != 0) return nullptr;
+  if ((*hwprobe_ptr)(g_hwprobes, 1, 0, nullptr, 0) != 0) return nullptr;
   return ret42;
 }
 
@@ -102,7 +102,11 @@
 #elif defined(__arm__)
   EXPECT_EQ(getauxval(AT_HWCAP), g_hwcap);
 #elif defined(__riscv)
+  printf("hwcap=%lx hwprobe_ptr=%p (__riscv_hwprobe=%p) null=%p\n", g_hwcap, g_hwprobe_ptr,
+         __riscv_hwprobe, g_null);
+
   EXPECT_EQ(getauxval(AT_HWCAP), g_hwcap);
+  EXPECT_EQ(nullptr, g_null);
 
   riscv_hwprobe probes[] = {{.key = RISCV_HWPROBE_KEY_IMA_EXT_0}};
   ASSERT_EQ(0, __riscv_hwprobe(probes, 1, 0, nullptr, 0));