Re-do static function dispatch.

Until now we had ifuncs for the string/memory routines in dynamic
executables but trivial one-line assembler stubs branching to the
default implementation in all cases for static executables. I did
recently experiment with running the ifuncs earlier in static
executables, but that actually broke one of our tests --- although our
internal ifuncs are built very carefully, an ifunc built as a test ends
up with shadow call stack trying to write and read x18 in the prolog and
epilog, but the shadow call stack (and x18) isn't set up yet, leading to
a crash (before any of the usual signal handlers have been installed,
so without any useful diagnostics).

While as far as I can tell, basically no-one outside of libc actually
uses ifuncs (in part because they're not available on non-Linux systems,
and if you're going to have to have a different implementation for other
OSes, you usually end up preferring to just use the same implementation
everywhere), *and* this only affects static executables, which are also
barely used in practice, I still don't fancy the app compat risk of
just saying "meh, anyone with ifuncs will have to make sure they're safe".

Which leads us to this change, which is basically a poor man's ifunc,
with function-scoped static function pointers as a poor man's GOT.
(Which means that, while not ideal performance-wise, this isn't actually
much worse than a dynamic executable.)

This change also factors out the typedefs, since there were a handful
of mistakes in some of the copies.

Test: run the static benchmarks on various architectures
Change-Id: Iec945b710174bebaa27cf71ed0101e7f5d769697

Author: enh-google

libc/Android.bp

@@ -1416,43 +1416,13 @@ cc_library_static {
 }
 
 // ========================================================
-// libc_static_dispatch.a --- libc.a ifuncs
+// libc_static_dispatch.a/libc_dynamic_dispatch.a --- string/memory "ifuncs"
+// (Actually ifuncs for libc.so, but a home-grown alternative for libc.a.)
 // ========================================================
-cc_library_static {
-    defaults: ["libc_defaults"],
-    name: "libc_static_dispatch",
 
-    arch: {
-        x86_64: {
-            srcs: ["arch-x86_64/static_function_dispatch.S"],
-        },
-        x86: {
-            srcs: ["arch-x86/static_function_dispatch.S"],
-        },
-        arm: {
-            srcs: ["arch-arm/static_function_dispatch.S"],
-        },
-        arm64: {
-            srcs: ["arch-arm64/static_function_dispatch.S"],
-        },
-        riscv64: {
-            srcs: ["arch-riscv64/static_function_dispatch.S"],
-        },
-    },
-}
-
-// ========================================================
-// libc_dynamic_dispatch.a --- libc.so ifuncs
-// ========================================================
-cc_library_static {
+cc_defaults {
+    name: "libc_dispatch_defaults",
     defaults: ["libc_defaults"],
-    name: "libc_dynamic_dispatch",
-
-    cflags: [
-        "-ffreestanding",
-        "-fno-stack-protector",
-        "-fno-jump-tables",
-    ],
     arch: {
         x86_64: {
             srcs: ["arch-x86_64/dynamic_function_dispatch.cpp"],
@@ -1470,6 +1440,30 @@ cc_library_static {
             srcs: ["arch-riscv64/dynamic_function_dispatch.cpp"],
         },
     },
+    // Prevent the compiler from inserting calls to libc/taking the address of
+    // a jump table from within an ifunc (or, in the static case, code that
+    // can be executed arbitrarily early).
+    cflags: [
+        "-ffreestanding",
+        "-fno-stack-protector",
+        "-fno-jump-tables",
+    ],
+}
+
+cc_library_static {
+    name: "libc_static_dispatch",
+    defaults: ["libc_dispatch_defaults"],
+    cflags: [
+        "-DBIONIC_STATIC_DISPATCH",
+    ],
+}
+
+cc_library_static {
+    name: "libc_dynamic_dispatch",
+    defaults: ["libc_dispatch_defaults"],
+    cflags: [
+        "-DBIONIC_DYNAMIC_DISPATCH",
+    ],
 }
 
 // ========================================================