subsections: don't lose the offset in the parent section

We don't want to lose the offset into the parent section when we
create a subsection, at least not for the MachO backend which is
currently the only user of subsections. Allow ofmt->herelabel() to set
a flag to copy the section offset from the previous section.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>

asm/labels.c

@@ -351,17 +351,25 @@ handle_herelabel(union label *lptr, int32_t *segment, int64_t *offset)
     if (oldseg == location.segment && *offset == location.offset) {
         /* This label is defined at this location */
         int32_t newseg;
+        bool copyoffset = false;
 
         nasm_assert(lptr->defn.mangled);
         newseg = ofmt->herelabel(lptr->defn.mangled, lptr->defn.type,
-                                 oldseg, &lptr->defn.subsection);
+                                 oldseg, &lptr->defn.subsection, &copyoffset);
         if (likely(newseg == oldseg))
             return;
 
         *segment = newseg;
+        if (copyoffset) {
+            /* Maintain the offset from the old to the new segment */
+            switch_segment(newseg);
+            location.offset = *offset;
+        } else {
+            /* Keep a separate offset for the new segment */
             *offset  = switch_segment(newseg);
         }
     }
+}
 
 static bool declare_label_lptr(union label *lptr,
                                enum label_type type, const char *special)

include/nasm.h

@@ -911,9 +911,14 @@ struct ofmt {
      * The offset isn't passed; and may not be stable at this point.
      * The subsection number is a field available for use by the
      * backend. It is initialized to NO_SEG.
+     *
+     * If "copyoffset" is set by the backend then the offset is
+     * copied from the previous segment, otherwise the new segment
+     * is treated as a new segment the normal way.
      */
     int32_t (*herelabel)(const char *name, enum label_type type,
-                         int32_t seg, int32_t *subsection);
+                         int32_t seg, int32_t *subsection,
+                         bool *copyoffset);
 
     /*
      * This procedure is called to modify section alignment,

output/outdbg.c

@@ -137,14 +137,17 @@ static int32_t dbg_section_names(char *name, int pass, int *bits)
 }
 
 static int32_t dbg_herelabel(const char *name, enum label_type type,
-                             int32_t oldseg, int32_t *subsection)
+                             int32_t oldseg, int32_t *subsection,
+                             bool *copyoffset)
 {
     int32_t newseg = oldseg;
     
     if (subsections_via_symbols && type != LBL_LOCAL) {
         newseg = *subsection;
-        if (newseg == NO_SEG)
+        if (newseg == NO_SEG) {
             newseg = *subsection = seg_alloc();
+            *copyoffset = true; /* Minic MachO for now */
+        }
     }
     fprintf(ofile, "herelabel %s type %d (seg %08x) -> %08x\n",
             name, type, oldseg, newseg);

output/outmacho.c

@@ -1018,7 +1018,8 @@ static int32_t macho_section(char *name, int pass, int *bits)
 }
 
 static int32_t macho_herelabel(const char *name, enum label_type type,
-			       int32_t section, int32_t *subsection)
+			       int32_t section, int32_t *subsection,
+			       bool *copyoffset)
 {
     struct section *s;
     int32_t subsec;
@@ -1043,6 +1044,7 @@ static int32_t macho_herelabel(const char *name, enum label_type type,
     }
 
     s->subsection = subsec;
+    *copyoffset = true;		/* Maintain previous offset */
     return subsec;
 }
 
@@ -1055,8 +1057,8 @@ static void macho_symdef(char *name, int32_t section, int64_t offset,
 
 #if defined(DEBUG) && DEBUG>2
     nasm_error(ERR_DEBUG,
-            " macho_symdef: %s, sec=%"PRIx32", off=%"PRIx64", is_global=%d, %s\n",
+            " macho_symdef: %s, pass0=%d, passn=%"PRId64", sec=%"PRIx32", off=%"PRIx64", is_global=%d, %s\n",
-            name, section, offset, is_global, special);
+	       name, pass0, passn, section, offset, is_global, special);
 #endif
 
     if (is_global == 3) {