Enable memory footprint dump on JSC in Linux

jsc-memdump.patch

diff --git a/Source/JavaScriptCore/jsc.cpp b/Source/JavaScriptCore/jsc.cpp
index ead01e20b7a..fa69e09e84e 100644
--- a/Source/JavaScriptCore/jsc.cpp
+++ b/Source/JavaScriptCore/jsc.cpp
@@ -140,17 +140,46 @@
 #if __has_include(<WebKitAdditions/MemoryFootprint.h>)
 #include <WebKitAdditions/MemoryFootprint.h>
 #else
+#include <unistd.h>
+#include <sys/resource.h>
 struct MemoryFootprint {
     uint64_t current;
     uint64_t peak;
     
     static MemoryFootprint now()
     {
-        return { 0L, 0L };
+        struct rusage ru;
+        getrusage(RUSAGE_SELF, &ru);
+        return { getCurrentMemoryUsage(), static_cast<uint64_t>(ru.ru_maxrss)*1024 };
+    }
+
+    static uint64_t getCurrentMemoryUsage()
+    {
+        long rss = 0L;
+        FILE* fp = fopen("/proc/self/statm", "r");
+        if (fp == NULL)
+            return 0L;
+        if (fscanf(fp, "%*s%ld", &rss) != 1 ) {
+            fclose(fp);
+            return 0L;
+        }
+        fclose(fp);
+        return static_cast<uint64_t>(rss) * static_cast<uint64_t>(sysconf(_SC_PAGESIZE));
     }
     
     static void resetPeak()
     {
+        // To reset the peak size, we need to write 5 to /proc/self/clear_refs
+        // as described in `man -s5 proc`, in the clear_refs section
+        FILE *f = fopen("/proc/self/clear_refs", "w");
+        if (!f) {
+            fprintf (stderr, "failed to reset peak\n");
+            return;
+        }
+        int written = write(fileno(f), "5", 1);
+        if(written != 1)
+            fprintf (stderr, "failed to reset peak\n");
+        fclose(f);
     }
 };
 #endif