From 131d9fba298e1bc7e3cbdab6097e68b87a0771ee Mon Sep 17 00:00:00 2001
From: Christian Hergert <chergert@redhat.com>
Date: Mon, 15 May 2023 13:30:41 -0700
Subject: [PATCH] libsysprof-analyze: implement kallsyms symbolizer

This does a simple binary search across the parsed kallsyms using the
addresses we've parsed. We need to be sure we've created the array properly
so that our bounds checking will prevent infinite loops in the tight
binary search loop.
---
 .../sysprof-kallsyms-symbolizer.c             | 72 ++++++++++++++++++-
 1 file changed, 69 insertions(+), 3 deletions(-)

diff --git a/src/libsysprof-analyze/sysprof-kallsyms-symbolizer.c b/src/libsysprof-analyze/sysprof-kallsyms-symbolizer.c
index 98a54d1c..7c4d0a78 100644
--- a/src/libsysprof-analyze/sysprof-kallsyms-symbolizer.c
+++ b/src/libsysprof-analyze/sysprof-kallsyms-symbolizer.c
@@ -38,6 +38,8 @@ struct _SysprofKallsymsSymbolizer
 {
   SysprofSymbolizer  parent_instance;
   GArray            *kallsyms;
+  guint64            low;
+  guint64            high;
 };
 
 struct _SysprofKallsymsSymbolizerClass
@@ -48,6 +50,7 @@ struct _SysprofKallsymsSymbolizerClass
 G_DEFINE_FINAL_TYPE (SysprofKallsymsSymbolizer, sysprof_kallsyms_symbolizer, SYSPROF_TYPE_SYMBOLIZER)
 
 static SysprofStrings *kallsym_strings;
+static GRefString *linux_string;
 
 static void
 kernel_symbol_clear (gpointer data)
@@ -76,6 +79,7 @@ sysprof_kallsyms_symbolizer_prepare_worker (GTask        *task,
   SysprofKallsymsSymbolizer *self = source_object;
   GDataInputStream *input = task_data;
   g_autoptr(GError) error = NULL;
+  guint64 last_address = 0;
   char *line;
   gsize len;
 
@@ -126,7 +130,14 @@ sysprof_kallsyms_symbolizer_prepare_worker (GTask        *task,
       /* Make @name usable as C string */
       *iter = 0;
 
-      sysprof_kallsyms_symbolizer_add (self, address, type, name);
+      /* Only add this if we're after the previous address so that
+       * we can be sure our sort is proper and will not break the
+       * tight loop in lookup binary search.
+       */
+      if (address > last_address)
+        sysprof_kallsyms_symbolizer_add (self, address, type, name);
+
+      last_address = address;
 
     failure:
       g_free (line);
@@ -136,6 +147,19 @@ sysprof_kallsyms_symbolizer_prepare_worker (GTask        *task,
    * We just trust that the kernel did that part correctly.
    */
 
+  /* Store a "best guess" at an lower/upper bound for the max address so that
+   * we can avoid searching for anything unreasonably past the end of the last
+   * kernel symbol.
+   */
+  if (self->kallsyms->len > 0)
+    {
+      const KernelSymbol *head = &g_array_index (self->kallsyms, KernelSymbol, 0);
+      const KernelSymbol *tail = &g_array_index (self->kallsyms, KernelSymbol, self->kallsyms->len-1);
+
+      self->low = head->address;
+      self->high = tail->address + 0xFFFF;
+    }
+
   g_task_return_boolean (task, TRUE);
 }
 
@@ -198,7 +222,48 @@ sysprof_kallsyms_symbolizer_symbolize (SysprofSymbolizer        *symbolizer,
                                        SysprofAddressContext     context,
                                        SysprofAddress            address)
 {
-  return NULL;
+  SysprofKallsymsSymbolizer *self = (SysprofKallsymsSymbolizer *)symbolizer;
+  const KernelSymbol *symbols;
+  guint n_symbols;
+  guint left;
+  guint right;
+  guint mid;
+
+  if (context != SYSPROF_ADDRESS_CONTEXT_KERNEL)
+    return NULL;
+
+  if (address < self->low || address >= self->high)
+    return NULL;
+
+  symbols = &g_array_index (self->kallsyms, KernelSymbol, 0);
+  n_symbols = self->kallsyms->len;
+
+  left = 0;
+  right = n_symbols;
+  mid = n_symbols / 2;
+
+  for (;;)
+    {
+      const KernelSymbol *ksym = &symbols[mid];
+      const KernelSymbol *next = &symbols[mid+1];
+
+      if (address >= ksym->address &&
+          (address < next->address || next->address == 0))
+        return _sysprof_symbol_new (g_ref_string_acquire (ksym->name),
+                                    g_ref_string_acquire (linux_string),
+                                    NULL,
+                                    ksym->address,
+                                    next->address ? next->address : ksym->address + 0xFFFF);
+
+      if (address < ksym->address)
+        right = mid;
+      else
+        left = mid + 1;
+
+      mid = left + ((right-left) / 2);
+    }
+
+  g_assert_not_reached ();
 }
 
 static void
@@ -224,12 +289,13 @@ sysprof_kallsyms_symbolizer_class_init (SysprofKallsymsSymbolizerClass *klass)
   symbolizer_class->symbolize = sysprof_kallsyms_symbolizer_symbolize;
 
   kallsym_strings = sysprof_strings_new ();
+  linux_string = g_ref_string_new_intern ("Linux");
 }
 
 static void
 sysprof_kallsyms_symbolizer_init (SysprofKallsymsSymbolizer *self)
 {
-  self->kallsyms = g_array_new (FALSE, FALSE, sizeof (KernelSymbol));
+  self->kallsyms = g_array_new (TRUE, FALSE, sizeof (KernelSymbol));
   g_array_set_clear_func (self->kallsyms, kernel_symbol_clear);
 }