i#2213 modgap: avoid double-mapping libs in drraw2trace (#2245)

For modules with gaps, drraw2trace now simply has the later segments point
at the first mapping, which should itself include the gap and the other
segments.  With all PC arithmetic using the absolute module base, rather
than segment bases, it all works out.

clients/drcachesim/tracer/raw2trace.cpp

@@ -123,6 +123,18 @@ raw2trace_t::read_and_map_modules(void)
             strcmp(info.path, "[vdso]") == 0) {
             // We won't be able to decode.
             modvec.push_back(module_t(info.path, info.start, NULL, 0));
+        } else if (info.containing_index != i) {
+            // For split segments, drmodtrack_lookup() gave the lowest base addr,
+            // so our PC offsets are from that.  We assume that the single mmap of
+            // the first segment thus includes the other segments and that we don't
+            // need another mmap.
+            VPRINT(1, "Separate segment assumed covered: module %d seg " PFX " = %s\n",
+                   (int)modvec.size(), (ptr_uint_t)info.start, info.path);
+            modvec.push_back(module_t(info.path,
+                                      // We want the low base not segment base.
+                                      modvec[info.containing_index].orig_base,
+                                      // 0 size indicates this is a secondary segment.
+                                      modvec[info.containing_index].map_base, 0));
         } else {
             size_t map_size;
             byte *base_pc = dr_map_executable_file(info.path, DR_MAPEXE_SKIP_WRITABLE,
@@ -152,7 +164,7 @@ raw2trace_t::unmap_modules(void)
         FATAL_ERROR("Failed to clean up module table data");
     for (std::vector<module_t>::iterator mvi = modvec.begin();
          mvi != modvec.end(); ++mvi) {
-        if (mvi->map_base != NULL) {
+        if (mvi->map_base != NULL && mvi->map_size != 0) {
             bool ok = dr_unmap_executable_file(mvi->map_base, mvi->map_size);
             if (!ok)
                 WARN("Failed to unmap module %s", mvi->path);