phrase clearer that the total size shown is not the exact size of the image on disk

Author: wirthi

docs/reference-manual/native-image/BuildOutput.md

@@ -24,7 +24,7 @@ Below is the example output when building a native executable of the `HelloWorld
 GraalVM Native Image: Generating 'helloworld' (executable)...
 ================================================================================
 [1/8] Initializing...                                            (2.8s @ 0.15GB)
- Java version: 20+34, vendor version: GraalVM CE 20-dev+34.1
+ Java version: 25+13, vendor version: GraalVM CE 25-dev+13.1
  Graal compiler: optimization level: 2, target machine: x86-64-v3
  C compiler: gcc (linux, x86_64, 12.2.0)
  Garbage collector: Serial GC (max heap size: 80% of RAM)
@@ -49,7 +49,7 @@ GraalVM Native Image: Generating 'helloworld' (executable)...
    7.03MB (32.02%) for image heap:   93,301 objects and 5 resources
    8.96MB (40.83%) for debug info generated in 1.0s
  659.13kB ( 2.93%) for other data
-  21.96MB in total
+  21.96MB in total image size, 21.04MB in total file size
 --------------------------------------------------------------------------------
 Top 10 origins of code area:            Top 10 object types in image heap:
    4.03MB java.base                        1.14MB byte[] for code metadata
@@ -201,6 +201,10 @@ The progress indicator is printed periodically at an increasing interval.
 ### <a name="stage-creating"></a>Creating Image
 In this stage, the native binary is created and written to disk.
 Debug info is also generated as part of this stage (if requested).
+This section breaks down the total image size as well as [code area](#glossary-code-area) and [image heap](#glossary-image-heap) (see below for more details).
+The total image size is calculated before linking by summing the sizes of the code area, image heap, debug information (if requested and embedded in the binary), and other data.
+The total file size is the actual size of the image on disk after linking.
+Typically, the file size is slightly smaller than the image size due to additional link time optimizations.
 
 #### <a name="glossary-code-area"></a>Code Area
 The code area contains machine code produced by the Graal compiler for all reachable methods.

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/NativeImageGenerator.java

@@ -734,6 +734,7 @@ protected void doRun(Map<Method, CEntryPointData> entryPoints, JavaMainSupport j
             compileQueue.purge();
 
             int numCompilations = codeCache.getOrderedCompilations().size();
+            int imageDiskFileSize = -1;
 
             try (StopTimer t = TimerCollection.createTimerAndStart(TimerCollection.Registry.WRITE)) {
                 loader.watchdog.recordActivity();
@@ -755,14 +756,21 @@ protected void doRun(Map<Method, CEntryPointData> entryPoints, JavaMainSupport j
 
                 AfterImageWriteAccessImpl afterConfig = new AfterImageWriteAccessImpl(featureHandler, loader, hUniverse, inv, tmpDir, image.getImageKind(), debug);
                 featureHandler.forEachFeature(feature -> feature.afterImageWrite(afterConfig));
+                try {
+                    // size changes during linking and afterConfig phase
+                    imageDiskFileSize = (int) inv.getOutputFile().toFile().length();
+                } catch (Exception e) {
+                    imageDiskFileSize = -1; // we can't read a disk file size
+                }
             }
             try (StopTimer t = TimerCollection.createTimerAndStart(TimerCollection.Registry.ARCHIVE_LAYER)) {
                 if (ImageLayerBuildingSupport.buildingSharedLayer()) {
                     ImageSingletonsSupportImpl.HostedManagement.persist();
                     HostedImageLayerBuildingSupport.singleton().archiveLayer(imageName);
                 }
             }
-            reporter.printCreationEnd(image.getImageFileSize(), heap.getLayerObjectCount(), image.getImageHeapSize(), codeCache.getCodeAreaSize(), numCompilations, image.getDebugInfoSize());
+            reporter.printCreationEnd(image.getImageFileSize(), heap.getLayerObjectCount(), image.getImageHeapSize(), codeCache.getCodeAreaSize(), numCompilations, image.getDebugInfoSize(),
+                            imageDiskFileSize);
         }
     }
 

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/ProgressReporter.java

@@ -584,7 +584,7 @@ public void setDebugInfoTimer(Timer timer) {
         this.debugInfoTimer = timer;
     }
 
-    public void printCreationEnd(int imageFileSize, int heapObjectCount, long imageHeapSize, int codeAreaSize, int numCompilations, int debugInfoSize) {
+    public void printCreationEnd(int imageFileSize, int heapObjectCount, long imageHeapSize, int codeAreaSize, int numCompilations, int debugInfoSize, int imageDiskFileSize) {
         recordJsonMetric(ImageDetailKey.IMAGE_HEAP_OBJECT_COUNT, heapObjectCount);
         Timer imageTimer = getTimer(TimerCollection.Registry.IMAGE);
         Timer writeTimer = getTimer(TimerCollection.Registry.WRITE);
@@ -620,7 +620,11 @@ public void printCreationEnd(int imageFileSize, int heapObjectCount, long imageH
         recordJsonMetric(ImageDetailKey.NUM_COMP_UNITS, numCompilations);
         l().a(format, ByteFormattingUtil.bytesToHuman(otherBytes), Utils.toPercentage(otherBytes, imageFileSize))
                         .doclink("other data", "#glossary-other-data").println();
-        l().a("%9s in total", ByteFormattingUtil.bytesToHuman(imageFileSize)).println();
+        l().a("%9s in total image size", ByteFormattingUtil.bytesToHuman(imageFileSize));
+        if (imageDiskFileSize >= 0) {
+            l().a(", %s in total file size", ByteFormattingUtil.bytesToHuman(imageDiskFileSize));
+        }
+        l().println();
         printBreakdowns();
         ImageSingletons.lookup(ProgressReporterFeature.class).afterBreakdowns();
         printRecommendations();