Support extern C ver direct updates

FIx minor RISC encodings.

5 files changed, 130 insertions, 6 deletions

diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter25Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter25Test.java
index 41225097..bde25ab7 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter25Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter25Test.java
@@ -21,6 +21,87 @@ import org.junit.Test;
 import static org.junit.Assert.*;
 
 public class Chapter25Test {
+    @Test
+    public void testExternData() throws IOException {
+        String src = """
+            i32 counter="C";
+            i8 small="C";
+            f64 fraction="C";
+            {int} bump="C";
+            val test_global={ ->
+                val before=counter;
+                counter=before;
+                counter=++counter+1;
+                counter+=1;
+                val mid=bump();
+                small++;
+                fraction=fraction+0.5;
+                return before*10000+mid*100+counter;
+            };
+            """;
+        TestC.runC(src,"extern_data","",-1);
+    }
+
+    @Test
+    public void testExternDataEncoding() {
+        for( String cpu : new String[]{"arm","riscv"} ) {
+            CodeGen code = new CheckedCodeGen("i32 counter=\"C\"; counter=counter+3; return counter;");
+            // Exercise signed low-12 relocation arithmetic, past the first page.
+            int addr = 0x3800;
+            code._externDataAddresses.put("counter",addr);
+            code.driver(cpu,"SystemV",true,false);
+            byte[] image = new byte[1<<20];
+            var bits = code._encoding._bits;
+            System.arraycopy(bits.buf(),0,image,0,bits.size());
+            if( cpu.equals("arm") ) {
+                EvalArm64 arm = new EvalArm64(image,1<<16);
+                arm.st4(addr,-7);
+                assertEquals(0,arm.step(1000));
+                assertEquals(-4,arm.regs[0]);
+                assertEquals(-4,arm.ld4s(addr));
+            } else {
+                EvalRisc5 r5 = new EvalRisc5(image,1<<16);
+                r5.st4(addr,-7);
+                assertEquals(0,r5.step(1000));
+                assertEquals(-4,r5.regs[10]);
+                assertEquals(-4,r5.ld4s(addr));
+            }
+        }
+    }
+
+    @Test
+    public void testExternDataImports() throws IOException {
+        Path dir = Files.createTempDirectory(Path.of("build/objs"),"extern_data_");
+        String globals = "i32 counter=\"C\"; val read={ -> counter; };";
+        CodeGen globalCode = new CodeGen(null,dir.toString(),null,"Globals",globals,126,true,TypeInteger.BOT)
+            .driver(TestC.CPU_PORT,TestC.CALL_CONVENTION,false,false);
+        var clz = globalCode.compunit()._clz;
+        int counter = clz.find("counter");
+        assertTrue(clz._fields[counter]._extern);
+        assertEquals(-1,clz.offset(counter));
+        assertEquals(clz.remove(counter).size(),clz.size());
+        // Load the serialized declaration and ideal graph from Globals.o.
+        String src = """
+            i32 counter="C";
+            val test_global={ ->
+                val before=Globals.counter;
+                Globals.counter=before+1;
+                counter+=2;
+                return before*100+Globals.read();
+            };
+            """;
+        Ary<String> paths = new Ary<>(new String[]{dir.toString()});
+        for( boolean imported : new boolean[]{true,false} ) {
+            Path root = dir.resolve(imported ? "binary" : "source");
+            Files.createDirectories(root.resolve("Main"));
+            if( !imported ) Files.writeString(root.resolve("Main/Globals.smp"),globals);
+            new CodeGen(root.toString(),root.toString(),imported ? paths : null,"Main",src,126,true,TypeInteger.BOT)
+                .driver(TestC.CPU_PORT,TestC.CALL_CONVENTION,false,false);
+            assertEquals("",TestC.gcc(root+"/Main.o","",TestC.C_DRIVERS_DIR+"extern_data_import.c",
+                (String)null,new Ary<>(new String[]{dir+"/Globals.o"}),root+"/main"+(TestC.OS.startsWith("Windows") ? ".exe" : "")));
+        }
+    }
+
     @Test public void testPrintingConstantPool() throws Exception {
         com.seaofnodes.simple.codegen.PrintRegTestSupport.checkConstantPool();
     }
@@ -312,6 +393,13 @@ return  rez < buf# ? 0 : sys.libc._exit(-2);
     }
 
     @Test
+    public void testErrnoAccessor() throws IOException {
+        String src = "sys.libc.close(-1); return sys.libc.errno()==0;";
+        TestC.run(src,"errnoAccessor",new Ary<>(new String[]{SYS_BLDDIR}),
+                  TestC.CALL_CONVENTION,null,null,"",-1);
+    }
+
+    @Test
     public void testBubbles() throws IOException {
         String src = Files.readString( Path.of("docs/examples/BubbleSort.smp"));
         String exe = TestC.compile(src,"BubbleSort",new Ary<>(new String[]{SYS_BLDDIR}),
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/EvalRisc5.java b/chapter25/src/test/java/com/seaofnodes/simple/EvalRisc5.java
index a4cc7044..633e931e 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/EvalRisc5.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/EvalRisc5.java
@@ -252,7 +252,7 @@ public class EvalRisc5 {
                     case 2 -> (rs1 < rs2) ? 1 : 0;
                     case 3 -> (rs1 < rs2) ? 1 : 0;
                     case 4 -> rs1 ^ rs2;
-                    case 5 -> (ir & 0x40000000) != 0 ? (rs1 >>> (rs2 & 0x3F)) : (rs1 >> (rs2 & 0x3F));
+                    case 5 -> (ir & 0x40000000) != 0 ? (rs1 >> (rs2 & 0x3F)) : (rs1 >>> (rs2 & 0x3F));
                     case 6 -> rs1 | rs2;
                     case 7 -> rs1 & rs2;
                     default -> rval;
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/progs/extern_data.c b/chapter25/src/test/java/com/seaofnodes/simple/progs/extern_data.c
new file mode 100644
index 00000000..9325f65e
--- /dev/null
+++ b/chapter25/src/test/java/com/seaofnodes/simple/progs/extern_data.c
@@ -0,0 +1,22 @@
+#include <stdint.h>
+#include <stdio.h>
+
+int32_t counter=7;
+int8_t small=-3;
+double fraction=1.25;
+
+int64_t bump(void) { counter+=5; return counter; }
+__attribute__((CALL_CONV)) extern int64_t test_global(void);
+
+int main(void) {
+    int64_t result=test_global();
+    if(result!=71515 || counter!=15 || small!=-2 || fraction!=1.75) {
+        printf("result=%lld counter=%d small=%d fraction=%g\n",
+               (long long)result,counter,small,fraction);
+        return 1;
+    }
+    // A second call must observe C's new values, not a Simple initialization copy.
+    counter=-2;
+    result=test_global();
+    return result!=-19394 || counter!=6 || small!=-1 || fraction!=2.25;
+}
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/progs/extern_data_import.c b/chapter25/src/test/java/com/seaofnodes/simple/progs/extern_data_import.c
new file mode 100644
index 00000000..f65e5c84
--- /dev/null
+++ b/chapter25/src/test/java/com/seaofnodes/simple/progs/extern_data_import.c
@@ -0,0 +1,14 @@
+#include <stdint.h>
+#include <stdio.h>
+
+int32_t counter=7;
+__attribute__((CALL_CONV)) extern int64_t test_global(void);
+
+int main(void) {
+    int64_t result=test_global();
+    if(result!=710 || counter!=10) {
+        printf("result=%lld counter=%d\n",(long long)result,counter);
+        return 1;
+    }
+    return 0;
+}
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/spill/README.md b/chapter25/src/test/java/com/seaofnodes/simple/spill/README.md
index fae44126..6c78d46f 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/spill/README.md
+++ b/chapter25/src/test/java/com/seaofnodes/simple/spill/README.md
@@ -27,11 +27,11 @@ Chapter 25 cannot parse all earlier sources unchanged. Adaptations are explicit:
 
 All entries replay **through RegAlloc**, checking scheduled register constraints.
 The historical phase column is provenance, not a promise to run those old native
-harnesses in Chapter 25. In particular, the adapted Bubble Sort still exposes a
-pre-existing ARM extern-data encoding limitation (`i32 errno="C"; return 0;` is
-sufficient to reproduce it). Allocation succeeds; ARM encoding does not. That
-separate failure remains in the backport queue. Do not count this corpus as
-historical runtime coverage.
+harnesses in Chapter 25. The adapted Bubble Sort retains its historical
+`i32 errno="C"` declaration for allocation comparability. Direct data bindings
+now encode on all three targets, but this declaration cannot link to a libc
+whose errno is thread-local or accessor-based. Current system-library code uses
+`libc.errno()` instead. Do not count this corpus as historical runtime coverage.
 
 `SpillStats` then compiles the current system library through encoding at seed
 456, and runs Chapter25Test with its existing seeds and native checks. Together