backwards relocs

Signed-off-by: lizzie <lizzie@eden-emu.dev>

externals/powah/powah_emit.hpp

@@ -138,14 +138,15 @@ struct Context {
     }
 
     void ApplyRelocs() {
-        for (auto const [index, info] : relocs) {
-            assert(labels[index] != 0); //label must have an addr
+        for (auto const &[index, info] : relocs) {
+            //assert(labels[index] != 0); //label must have an addr
+            int32_t rel = (int32_t)labels[index] - (int32_t)info.offset;
             switch (info.kind) {
             case RelocKind::FormB:
-                base[info.offset] |= bitExt(labels[index] - info.offset, 16, 14);
+                base[info.offset] |= bitExt(rel, 16, 14);
                 break;
             case RelocKind::FormI:
-                base[info.offset] |= bitExt(labels[index] - info.offset, 6, 24);
+                base[info.offset] |= bitExt(rel, 6, 24);
                 break;
             }
         }
@@ -176,7 +177,7 @@ struct Context {
     }
 
     uint32_t bitExt(uint32_t value, uint32_t offs, uint32_t n) {
-        uint32_t mask = (1UL << (n + 1)) - 1;
+        uint32_t mask = (1UL << n) - 1;
         return (value & mask) << (32 - (n + offs));
     }
     void emit_XO(uint32_t op, GPR const rt, GPR const ra, GPR const rb, bool oe, bool rc) {

externals/powah/tests.cpp

@@ -141,7 +141,19 @@ TEST_CASE("ppc64: rotldi", "[ppc64]") {
     REQUIRE(data[12] == EB32(0x7823837c));
 }
 
-#if 1 //&& defined(ARCHITECTURE_ppc64)
+TEST_CASE("ppc64: branch-backwards", "[ppc64]") {
+    std::vector<uint32_t> data(64);
+    powah::Context ctx(data.data(), data.size());
+    powah::Label l_3 = ctx.DefineLabel();
+    ctx.LABEL(l_3);
+    ctx.ADD(powah::R1, powah::R2, powah::R3);
+    ctx.B(l_3);
+    ctx.ApplyRelocs();
+    REQUIRE(data[0] == EB32(0x141a227c));
+    REQUIRE(data[1] == EB32(0xfcffff4b));
+}
+
+#if defined(ARCHITECTURE_ppc64)
 /*
     0: d619637c  	mullw 3, 3, 3
     4: 20006378  	clrldi	3, 3, 32
@@ -221,6 +233,7 @@ TEST_CASE("ppc64: live-exec xoralu", "[ppc64]") {
     };
     auto* fn = (int (*)(int, int, int))data;
     REQUIRE(fn(0, 1, 2) == orig(0, 1, 2));
+    REQUIRE(fn(6456, 4564, 4564561) == orig(6456, 4564, 4564561));
 
     munmap((void*)data, 4096);
 }