Yeah, this actually works!

common.mk

@@ -1105,6 +1105,10 @@ incs: $(INSNS) {$(VPATH)}node_name.inc {$(VPATH)}known_errors.inc \
 
 insns: $(INSNS)
 
+ujit_examples.h: gen_ujit_examples.rb vm.$(OBJEXT)
+	$(ECHO) generating $@
+	$(Q) $(BASERUBY) gen_ujit_examples.rb
+
 id.h: $(tooldir)/generic_erb.rb $(srcdir)/template/id.h.tmpl $(srcdir)/defs/id.def
 	$(ECHO) generating $@
 	$(Q) $(BASERUBY) $(tooldir)/generic_erb.rb --output=$@ \
@@ -7002,6 +7006,7 @@ iseq.$(OBJEXT): {$(VPATH)}util.h
 iseq.$(OBJEXT): {$(VPATH)}vm_callinfo.h
 iseq.$(OBJEXT): {$(VPATH)}vm_core.h
 iseq.$(OBJEXT): {$(VPATH)}vm_opts.h
+iseq.$(OBJEXT): {$(VPATH)}ujit_examples.h
 load.$(OBJEXT): $(CCAN_DIR)/check_type/check_type.h
 load.$(OBJEXT): $(CCAN_DIR)/container_of/container_of.h
 load.$(OBJEXT): $(CCAN_DIR)/list/list.h

compile.c

@@ -856,6 +856,8 @@ rb_iseq_compile_node(rb_iseq_t *iseq, const NODE *node)
     return iseq_setup(iseq, ret);
 }
 
+extern uint8_t *native_pop_code; // TODO global hack
+
 static int
 rb_iseq_translate_threaded_code(rb_iseq_t *iseq)
 {
@@ -868,6 +870,9 @@ rb_iseq_translate_threaded_code(rb_iseq_t *iseq)
 	int insn = (int)iseq->body->iseq_encoded[i];
 	int len = insn_len(insn);
 	encoded[i] = (VALUE)table[insn];
+
+        if (insn == BIN(pop)) encoded[i] = (VALUE)native_pop_code;
+
 	i += len;
     }
     FL_SET((VALUE)iseq, ISEQ_TRANSLATED);

gen_ujit_examples.rb

@@ -2,7 +2,7 @@ def get_example_instruction_id
   # TODO we could get this from the script that generates vm.inc instead of dothings this song and dance
   `dwarfdump --name='YARVINSN_ujit_call_example' vm.o`.each_line do |line|
     if (id = line[/DW_AT_const_value\s\((\d+\))/, 1])
-      p [__method__, line]
+      p [__method__, line] if $DEBUG
       return id.to_i
     end
   end
@@ -13,7 +13,7 @@ def get_fileoff
   # use the load command to figure out the offset to the start of the content of vm.o
   `otool -l vm.o`.each_line do |line|
     if (fileoff = line[/fileoff (\d+)/, 1])
-      p [__method__, line]
+      p [__method__, line] if $DEBUG
       return fileoff.to_i
     end
   end
@@ -23,7 +23,7 @@ end
 def get_symbol_offset(symbol)
   `nm vm.o`.each_line do |line|
     if (offset = line[Regexp.compile('(\h+).+' + Regexp.escape(symbol) + '\Z'), 1])
-      p [__method__, line]
+      p [__method__, line] if $DEBUG
       return Integer(offset, 16)
     end
   end
@@ -42,15 +42,16 @@ def disassemble(offset)
   puts "feel free to verify with --reloc"
   disassembly = `#{command}`
   instructions = []
-  puts disassembly
+  puts disassembly if $DEBUG
   disassembly.each_line do |line|
     line = line.strip
-    match = /\h+: ((?:\h\h\s?)+)\s+(\w+)/.match(line) do |match_data|
+    match_data = /\h+: ((?:\h\h\s?)+)\s+(\w+)/.match(line)
+    if match_data
       bytes = match_data[1]
       mnemonic = match_data[2]
       instructions << [bytes, mnemonic, line]
-    end
+      break if mnemonic == 'jmp'
-    if !match && !instructions.empty?
+    elsif !instructions.empty?
       p line
       raise "expected a continuous sequence of disassembly lines"
     end
@@ -70,7 +71,7 @@ def disassemble(offset)
   call_idx = handler_instructions.find_index { |_, mnemonic, _| mnemonic == 'call' }
 
 
-  puts "\n\nDisassembly for the handler:"
+  puts "Disassembly for the example handler:"
   puts handler_instructions.map{|_,_,line|line}
 
   pre_call_bytes = []
@@ -78,28 +79,30 @@ def disassemble(offset)
   handler_instructions.take(call_idx).each do |bytes, mnemonic, _|
     pre_call_bytes += bytes.split
   end
-  handler_instructions[((call_idx+1)...)].each do |bytes, _, _|
+  handler_instructions[call_idx + 1, handler_instructions.size].each do |bytes, _, _|
     post_call_bytes += bytes.split
   end
 
   File.write("ujit_examples.h", <<-EOF)
-static const uint8_t ujit_precall_bytes[] = { #{pre_call_bytes.map{ |byte| '0x'+byte}.join(', ')} };
+static const uint8_t ujit_pre_call_bytes[] = { #{pre_call_bytes.map{ |byte| '0x'+byte}.join(', ')} };
-static const uint8_t ujit_postall_bytes[] = { #{post_call_bytes.map{ |byte| '0x'+byte}.join(', ')} };
+static const uint8_t ujit_post_call_bytes[] = { #{post_call_bytes.map{ |byte| '0x'+byte}.join(', ')} };
   EOF
-  puts "file:"
+  if $DEBUG
-  puts File.binread("ujit_examples.h")
+    puts "file:"
+    puts File.binread("ujit_examples.h")
+  end
 end
 
 instruction_id = get_example_instruction_id
 fileoff = get_fileoff
 tc_table_offset = get_symbol_offset('vm_exec_core.insns_address_table')
 vm_exec_core_offset = get_symbol_offset('vm_exec_core')
-p instruction_id
+p instruction_id if $DEBUG
-p fileoff
+p fileoff if $DEBUG
-p tc_table_offset.to_s(16)
+p tc_table_offset.to_s(16) if $DEBUG
 offset_to_insn_in_tc_table = fileoff + tc_table_offset + 8 * instruction_id
-p offset_to_insn_in_tc_table
+p offset_to_insn_in_tc_table if $DEBUG
 offset_to_handler_code_from_vm_exec_core = readint8b(offset_to_insn_in_tc_table)
-p offset_to_handler_code_from_vm_exec_core
+p offset_to_handler_code_from_vm_exec_core if $DEBUG
 disassemble(vm_exec_core_offset + offset_to_handler_code_from_vm_exec_core)
 

iseq.c

@@ -42,6 +42,10 @@
 #include "builtin.h"
 #include "insns.inc"
 #include "insns_info.inc"
+#include <sys/mman.h>
+#include "ujit_examples.h"
+
+uint8_t *native_pop_code; // TODO: hack. see addr2insn
 
 VALUE rb_cISeq;
 static VALUE iseqw_new(const rb_iseq_t *iseq);
@@ -3205,6 +3209,22 @@ rb_vm_encoded_insn_data_table_init(void)
         st_add_direct(encoded_insn_data, key1, (st_data_t)&insn_data[insn]);
         st_add_direct(encoded_insn_data, key2, (st_data_t)&insn_data[insn]);
     }
+
+    native_pop_code = mmap(0, 4096, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_ANON|MAP_PRIVATE, 0, 0);
+    if (native_pop_code == MAP_FAILED) rb_bug("mmap failed");
+    uint8_t *head = native_pop_code;
+    memcpy(head, ujit_pre_call_bytes, sizeof(ujit_pre_call_bytes));
+    head += sizeof(ujit_pre_call_bytes);
+    const uint8_t handmade_pop[] = {           // TODO assmeble this from a separate file
+       0x48, 0x83, 0x6f, 0x08, 0x08,         //	subq	$8, 8(%rdi)
+       0x48, 0x83, 0xc6, 0x08,               //	addq	$8, %rsi
+       0x48, 0x89, 0x37,                     //	movq	%rsi, (%rdi)
+       0x48, 0x89, 0xf0                      //	movq	%rsi, %rax
+    };
+    memcpy(head, handmade_pop, sizeof(handmade_pop));
+    head += sizeof(handmade_pop);
+    memcpy(head, ujit_post_call_bytes, sizeof(ujit_post_call_bytes));
+    // TODO this is small enough to fit in the page we allocated but that can change
 }
 
 int
@@ -3218,6 +3238,12 @@ rb_vm_insn_addr2insn(const void *addr)
         return (int)e->insn;
     }
 
+    // TODO this is a hack. The proper way to do this is to refactor this so that it takes
+    // the iseq body.
+    if (addr && addr == native_pop_code) {
+        return BIN(pop);
+    }
+
     rb_bug("rb_vm_insn_addr2insn: invalid insn address: %p", addr);
 }
 
@@ -3248,6 +3274,12 @@ encoded_iseq_trace_instrument(VALUE *iseq_encoded_insn, rb_event_flag_t turnon,
         return e->insn_len;
     }
 
+    // TODO this is a hack. The proper way to do this is to refactor this so that it takes
+    // the iseq body.
+    if (key && (uint8_t *)key == native_pop_code) {
+        return insn_len(BIN(pop));
+    }
+
     rb_bug("trace_instrument: invalid insn address: %p", (void *)*iseq_encoded_insn);
 }
 
@@ -3456,7 +3488,7 @@ trace_set_i(void *vstart, void *vend, size_t stride, void *data)
 }
 
 VALUE *
-rb_ujit_empty_func(rb_control_frame_t *cfp)
+rb_ujit_empty_func(rb_control_frame_t *cfp, const VALUE *pc)
 {
     // okay, not really empty, so maybe think of another name.
     // it's put in this file instead of say, compile.c to dodge long C compile time.

iseq.h

@@ -313,7 +313,7 @@ VALUE rb_iseq_defined_string(enum defined_type type);
 /* vm.c */
 VALUE rb_iseq_local_variables(const rb_iseq_t *iseq);
 
-NOINLINE(VALUE *rb_ujit_empty_func(rb_control_frame_t *cfp));
+NOINLINE(VALUE *rb_ujit_empty_func(rb_control_frame_t *cfp, const VALUE *pc));
 
 
 RUBY_SYMBOL_EXPORT_END

tool/ruby_vm/views/vm.inc.erb

@@ -34,7 +34,7 @@ INSN_ENTRY(<%= insn.name %>)
     START_OF_ORIGINAL_INSN(<%= insn.name %>);
     // assumes USE_MACHINE_REGS, aka reg_pc setup,
     // aka #define SET_PC(x) (reg_cfp->pc = reg_pc = (x))
-    reg_pc = rb_ujit_empty_func(GET_CFP());
+    reg_pc = rb_ujit_empty_func(GET_CFP(), reg_pc);
     END_INSN(<%= insn.name %>);
 }
 % end