base: add symbol support for dynamic libraries

Libraries are loaded into the process address space using the
mmap system call. Conveniently, this happens to be a good
time to update the process symbol table with the library's
incoming symbols so we handle the table update from within the
system call.

This works just like an application's normal symbols. The only
difference between a dynamic library and a main executable is
when the symbol table update occurs. The symbol table update for
an executable happens at program load time and is finished before
the process ever begins executing. Since dynamic linking happens
at runtime, the symbol loading happens after the library is
first loaded into the process address space. The library binary
is examined at this time for a symbol section and that section
is parsed for symbol types with specific bindings (global,
local, weak). Subsequently, these symbols are added to the table
and are available for use by gem5 for things like trace
generation.

Checkpointing should work just as it did previously. The address
space (and therefore the library) will be recorded and the symbol
table will be entirely recorded. (It's not possible to do anything
clever like checkpoint a program and then load the program back
with different libraries with LD_LIBRARY_PATH, because the
library becomes part of the address space after being loaded.)

1 files changed, 37 insertions, 12 deletions

diff --git a/src/base/loader/elf_object.cc b/src/base/loader/elf_object.cc
index fb5ec4c14..73c1c5dcd 100644
--- a/src/base/loader/elf_object.cc
+++ b/src/base/loader/elf_object.cc
@@ -396,7 +396,8 @@ ElfObject::ElfObject(const std::string &_filename, size_t _len,
 
 
 bool
-ElfObject::loadSomeSymbols(SymbolTable *symtab, int binding, Addr mask)
+ElfObject::loadSomeSymbols(SymbolTable *symtab, int binding, Addr mask,
+                           Addr base, Addr offset)
 {
     if (!symtab)
         return false;
@@ -432,9 +433,11 @@ ElfObject::loadSomeSymbols(SymbolTable *symtab, int binding, Addr mask)
                 if (GELF_ST_BIND(sym.st_info) == binding) {
                     char *sym_name = elf_strptr(elf, shdr.sh_link, sym.st_name);
                     if (sym_name && sym_name[0] != '$') {
-                        DPRINTF(Loader, "Symbol: %-40s value %#x\n",
-                                sym_name, sym.st_value);
-                        symtab->insert(sym.st_value & mask, sym_name);
+                        Addr value = sym.st_value - base + offset;
+                        if (symtab->insert(value & mask, sym_name)) {
+                            DPRINTF(Loader, "Symbol: %-40s value %#x\n",
+                                    sym_name, value);
+                        }
                     }
                 }
             }
@@ -449,23 +452,45 @@ ElfObject::loadSomeSymbols(SymbolTable *symtab, int binding, Addr mask)
 }
 
 bool
-ElfObject::loadGlobalSymbols(SymbolTable *symtab, Addr addr_mask)
+ElfObject::loadAllSymbols(SymbolTable *symtab, Addr base, Addr offset,
+                          Addr addr_mask)
 {
-    return loadSomeSymbols(symtab, STB_GLOBAL, addr_mask);
+    return (loadGlobalSymbols(symtab, base, offset, addr_mask) &&
+            loadLocalSymbols(symtab, base, offset, addr_mask) &&
+            loadWeakSymbols(symtab, base, offset, addr_mask));
 }
 
 bool
-ElfObject::loadLocalSymbols(SymbolTable *symtab, Addr addr_mask)
+ElfObject::loadGlobalSymbols(SymbolTable *symtab, Addr base, Addr offset,
+                             Addr addr_mask)
 {
-    bool found_local = loadSomeSymbols(symtab, STB_LOCAL, addr_mask);
-    bool found_weak = loadSomeSymbols(symtab, STB_WEAK, addr_mask);
-    return found_local || found_weak;
+    if (interpreter) {
+        interpreter->loadSomeSymbols(symtab, STB_GLOBAL, addr_mask,
+                                     base, offset);
+    }
+    return loadSomeSymbols(symtab, STB_GLOBAL, addr_mask, base, offset);
 }
 
 bool
-ElfObject::loadWeakSymbols(SymbolTable *symtab, Addr addr_mask)
+ElfObject::loadLocalSymbols(SymbolTable *symtab, Addr base, Addr offset,
+                            Addr addr_mask)
 {
-    return loadSomeSymbols(symtab, STB_WEAK, addr_mask);
+    if (interpreter) {
+        interpreter->loadSomeSymbols(symtab, STB_LOCAL, addr_mask,
+                                     base, offset);
+    }
+    return loadSomeSymbols(symtab, STB_LOCAL, addr_mask, base, offset);
+}
+
+bool
+ElfObject::loadWeakSymbols(SymbolTable *symtab, Addr base, Addr offset,
+                           Addr addr_mask)
+{
+    if (interpreter) {
+        interpreter->loadSomeSymbols(symtab, STB_WEAK, addr_mask,
+                                     base, offset);
+    }
+    return loadSomeSymbols(symtab, STB_WEAK, addr_mask, base, offset);
 }
 
 bool