Refactored SymbolInfo to lower memory usage in RTS

Previously as part of #11223 a new struct `SymbolInfo` was introduced to
keep track it the weak symbol status of a symbol.

This structure also kept a copy of the calculated address of the symbol
which turns out was useful in ignoring non-weak zero-valued symbols.

The information was kept in an array so it means for every symbol two
extra bytes were kept even though the vast majority of symbols are
non-weak and non-zero valued.

This changes the array into a sparse map keeping this information only
for the symbols that are weak or zero-valued. This allows for a
reduction in the amount of information needed to be kept while giving up
a small (negligable) hit in performance as this information now has to
be looked up in hashmaps.

Test Plan: ./validate on all platforms that use the runtime linker.

For unix platforms please ensure `DYNAMIC_GHC_PROGRAMS=NO` is added to
your validate file.

Reviewers: simonmar, austin, erikd, bgamari

Reviewed By: simonmar, bgamari

Subscribers: thomie, #ghc_windows_task_force

Differential Revision: https://phabricator.haskell.org/D2184

GHC Trac Issues: #11816

1 files changed, 7 insertions, 16 deletions

diff --git a/rts/LinkerInternals.h b/rts/LinkerInternals.h
index b311a8f341..815180c757 100644
--- a/rts/LinkerInternals.h
+++ b/rts/LinkerInternals.h
@@ -10,6 +10,7 @@
 #define LINKERINTERNALS_H
 
 #include "Rts.h"
+#include "Hash.h"
 
 /* See Linker.c Note [runtime-linker-phases] */
 typedef enum {
@@ -99,20 +100,6 @@ typedef struct {
 } SymbolExtra;
 
 
-/* Top-level structure for an symbols in object module.  One of these is allocated
-* for each symbol in an object in use.
-*/
-typedef struct _SymbolInfo {
-    /* The name of the symbol. */
-    char*          name;
-
-    /* The address of the symbol. */
-    void* addr;
-
-    /* Indicates if the symbol is weak */
-    HsBool isWeak;
-} SymbolInfo;
-
 /* Top-level structure for an object module.  One of these is allocated
  * for each object file in use.
  */
@@ -131,8 +118,8 @@ typedef struct _ObjectCode {
        this object into the global symbol hash table.  This is so that
        we know which parts of the latter mapping to nuke when this
        object is removed from the system. */
-    SymbolInfo* symbols;
-    int         n_symbols;
+    char** symbols;
+    int    n_symbols;
 
     /* ptr to mem containing the object file image */
     char*      image;
@@ -178,6 +165,10 @@ typedef struct _ObjectCode {
        execute code from it. */
     HsBool isImportLib;
 
+    /* Holds the list of symbols in the .o file which
+       require extra information.*/
+    HashTable *extraInfos;
+
 } ObjectCode;
 
 #define OC_INFORMATIVE_FILENAME(OC)             \