i#2062 non-module offline: add workaround for vdso

Adds a temporary workaround for vdso code where we just drop the ifetch
entries, to avoid a fatal error up front mapping modules.

Review-URL: https://codereview.appspot.com/307690043

clients/drcachesim/tracer/instru_offline.cpp

@@ -248,7 +248,7 @@ offline_instru_t::instrument_instr(void *drcontext, void *tag, void **bb_field,
 
     pc = dr_fragment_app_pc(tag);
     if (drmodtrack_lookup(drcontext, pc, &modidx, &modbase) != DRCOVLIB_SUCCESS) {
-        // FIXME i#1729: add non-module support.  The plan for instrs is to have
+        // FIXME i#2062: add non-module support.  The plan for instrs is to have
         // one entry w/ the start abs pc, and subsequent entries that pack the instr
         // length for 10 instrs, 4 bits each, into a pc.modoffs field.  We will
         // also need to store the type (read/write/prefetch*) and size for the

clients/drcachesim/tracer/raw2trace.cpp

@@ -118,7 +118,11 @@ raw2trace_t::read_and_map_modules(void)
         if (drmodtrack_offline_lookup(modhandle, i, &modbase, &modsize, &path) !=
             DRCOVLIB_SUCCESS)
             FATAL_ERROR("Failed to query module file");
-        if (strcmp(path, "<unknown>") == 0) {
+        if (strcmp(path, "<unknown>") == 0 ||
+            // i#2062: VDSO is hard to decode so for now we treat is as non-module.
+            // FIXME: currently we're dropping the ifetch data: we need the tracer
+            // to identify it instead of us, which requires drmodtrack changes.
+            strcmp(path, "[vdso]") == 0) {
             // We won't be able to decode.
             modvec.push_back(module_t(path, modbase, NULL, 0));
         } else {
@@ -297,7 +301,7 @@ raw2trace_t::append_bb_entries(uint tidx, offline_entry_t *in_entry)
     app_pc pc, decode_pc = start_pc;
     if ((in_entry->pc.modidx == 0 && in_entry->pc.modoffs == 0) ||
         modvec[in_entry->pc.modidx].map_base == NULL) {
-        // FIXME i#1729: add support for code not in a module (vsyscall, JIT, etc.).
+        // FIXME i#2062: add support for code not in a module (vsyscall, JIT, etc.).
         // Once that support is in we can remove the bool return value and handle
         // the memrefs up here.
         VPRINT(3, "Skipping ifetch for %u instrs not in a module\n", instr_count);