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, 72 insertions, 0 deletions

diff --git a/rts/RtsSymbolInfo.c b/rts/RtsSymbolInfo.c
new file mode 100644
index 0000000000..6688d9c9ba
--- /dev/null
+++ b/rts/RtsSymbolInfo.c
@@ -0,0 +1,72 @@
+/* -----------------------------------------------------------------------------
+ *
+ * (c) The GHC Team, 2000-2015
+ *
+ * RTS Symbols
+ *
+ * ---------------------------------------------------------------------------*/
+
+#include "ghcplatform.h"
+#include "RtsSymbolInfo.h"
+
+#include "Rts.h"
+#include "HsFFI.h"
+
+#include "Hash.h"
+#include "RtsUtils.h"
+
+typedef struct _SymbolInfo {
+    /* Determines if the
+       symbol is weak */
+    HsBool isWeak;
+
+} SymbolInfo;
+
+/* -----------------------------------------------------------------------------
+* Performs a check to see if the symbol at the given address
+* is a weak symbol or not.
+*
+* Returns: HS_BOOL_TRUE on symbol being weak, else HS_BOOL_FALSE
+*/
+HsBool isSymbolWeak(ObjectCode *owner, void *label)
+{
+    SymbolInfo *info;
+    if (owner
+        && label
+        && owner->extraInfos
+        && (info = lookupStrHashTable(owner->extraInfos, label)) != NULL)
+    {
+        return info->isWeak;
+    }
+
+    return HS_BOOL_FALSE;
+}
+
+/* -----------------------------------------------------------------------------
+* Marks the symbol at the given address as weak or not.
+* If the extra symbol infos table has not been initialized
+* yet this will create and allocate a new Hashtable
+*/
+void setWeakSymbol(ObjectCode *owner, void *label)
+{
+    SymbolInfo *info;
+    if (owner && label)
+    {
+        info = NULL;
+        if (!owner->extraInfos)
+        {
+            owner->extraInfos = allocStrHashTable();
+        }
+        else {
+            info = lookupStrHashTable(owner->extraInfos, label);
+        }
+
+        if (!info){
+            info = stgMallocBytes(sizeof(SymbolInfo), "setWeakSymbol");
+        }
+
+        info->isWeak = HS_BOOL_TRUE;
+
+        insertStrHashTable(owner->extraInfos, label, info);
+    }
+}