add simple patching mechanism

4 files changed, 68 insertions, 2 deletions

diff --git a/src/copyjit.c b/src/copyjit.c
index 393c8e1..0de85d3 100644
--- a/src/copyjit.c
+++ b/src/copyjit.c
@@ -471,6 +471,23 @@ void compile_start(ctx_t *ctx)
 	ctx->pc = ctx->buf;
 }
 
+reloc_t compile_placeholder(ctx_t *ctx, compile_callback_t call)
+{
+	reloc_t r = {0};
+	r.addr = call(ctx, 0);
+
+	/* the immediate is the last sizeof(uintptr_t) bytes of the generated
+	 * instruction
+	 * (at least we assume, the user could've passed anything to our callback) */
+	r.imm = ((uintptr_t *)ctx->pc) - 1;
+	return r;
+}
+
+void compile_patch(reloc_t reloc, void *addr)
+{
+	*reloc.imm = (uintptr_t)addr;
+}
+
 void compile_finish(ctx_t *ctx)
 {
 	__builtin___clear_cache(ctx->buf, ctx->buf + ctx->size);
diff --git a/src/copyjit.h b/src/copyjit.h
index d752144..8170204 100644
--- a/src/copyjit.h
+++ b/src/copyjit.h
@@ -3,12 +3,21 @@
 #ifndef HMMJIT_H
 #define HMMJIT_H
 
+#include <stdint.h>
+
 typedef struct {
 	char *pc;
 	char *buf;
 	size_t size;
 } ctx_t;
 
+typedef struct {
+	void *addr;
+	uintptr_t *imm;
+} reloc_t;
+
+typedef void *(*compile_callback_t)(ctx_t *, unsigned long);
+
 #include "../lib/op_decls.h"
 #include "../lib/imm_decls.h"
 
@@ -30,6 +39,9 @@ void *compile_sly(ctx_t *ctx, unsigned long i);
 /** @todo add in placeholders (for example for load immediate but we don't know
  * what the immediate is yet) */
 
+reloc_t compile_placeholder(ctx_t *ctx, compile_callback_t call);
+void compile_patch(reloc_t reloc, void *addr);
+
 void compile_start(ctx_t *ctx);
 void compile_finish(ctx_t *ctx);
 unsigned long run(ctx_t *ctx);
diff --git a/tests/check b/tests/check
index b079a57..a904b37 100755
--- a/tests/check
+++ b/tests/check
diff --git a/tests/check.c b/tests/check.c
index 8f4c6de..f6e775c 100644
--- a/tests/check.c
+++ b/tests/check.c
@@ -138,8 +138,45 @@ static void check_add()
 
 static void check_branch()
 {
-	/* oh yeah, I don't support forward references (yet), so this is a bit
-	 * tricky */
+	for (size_t i = 0; i < 2; ++i) {
+		ctx_t ctx;
+		compile_start(&ctx);
+
+		compile_fast_lia(&ctx, i);
+		reloc_t r = compile_placeholder(&ctx, compile_lio);
+		compile_ban(&ctx);
+
+		compile_lix(&ctx, 0);
+		compile_end(&ctx);
+
+		void *skip = compile_lix(&ctx, 1);
+		compile_end(&ctx);
+		compile_patch(r, skip);
+
+		compile_finish(&ctx);
+
+		assert(run(&ctx) == (i != 0));
+	}
+
+	for (size_t i = 0; i < 2; ++i) {
+		ctx_t ctx;
+		compile_start(&ctx);
+
+		compile_fast_lia(&ctx, i);
+		reloc_t r = compile_placeholder(&ctx, compile_lio);
+		compile_baz(&ctx);
+
+		compile_lix(&ctx, 0);
+		compile_end(&ctx);
+
+		void *skip = compile_lix(&ctx, 1);
+		compile_end(&ctx);
+		compile_patch(r, skip);
+
+		compile_finish(&ctx);
+
+		assert(run(&ctx) == (i == 0));
+	}
 }
 
 int main()