Spread control: add server RandomSeed GOT diagnostic/override

1 files changed, 61 insertions, 0 deletions

diff --git a/src/hl2h.cpp b/src/hl2h.cpp
index ee2e990..90e0990 100644
--- a/src/hl2h.cpp
+++ b/src/hl2h.cpp
@@ -2,6 +2,8 @@
 #include "hl2h.h"
 #include <cmath>
 #include <cstdarg>
+#include <cstdlib>
+#include <sys/mman.h>
 
 // ---------------------------------------------------------------------------
 // logging
@@ -403,7 +405,66 @@ static bool jumpbug_apply(CUserCmd *cmd, int local, void *ent, int flags,
   return cmd->buttons != before;
 }
 
+// ---------------------------------------------------------------------------
+// server RandomSeed diagnostic / override
+// ---------------------------------------------------------------------------
+//
+// The installed 2024 server build is stripped and its usercmd/server-random-seed
+// handling differs from the 2013 SDK source. This hook is installed on the
+// server.so GOT slot for RandomSeed (R_386_JUMP_SLOT at vaddr 0xce1348) so we
+// can see which seed FireBullets actually uses and optionally force the chosen
+// spread seed. Disabled unless HL2H_SEED_TRACE / HL2H_SEED_FORCE are set.
+
+static void (*g_real_random_seed)(int) = nullptr;
+static uintptr_t g_srv_base = 0;
+static bool g_seed_hook_installed = false;
+
+static void hkdSrvRandomSeed(int seed) {
+  uintptr_t ret = (uintptr_t)__builtin_return_address(0);
+  long off = (long)(ret - g_srv_base);
+  static bool trace = getenv("HL2H_SEED_TRACE") != nullptr;
+  static bool force = getenv("HL2H_SEED_FORCE") != nullptr;
+  static int logs = 0;
+  bool bullet_site = (off >= 0x216900 && off <= 0x216930);
+  if (trace && (bullet_site || logs < 12)) {
+    if (logs < 200) {
+      logs++;
+      logf("srvseed: seed=%d off=0x%lx bullet=%d", seed, off,
+           (int)bullet_site);
+    }
+  }
+  if (force && bullet_site)
+    seed = 33;
+  if (g_real_random_seed)
+    g_real_random_seed(seed);
+}
+
+static void install_seed_hook() {
+  if (g_seed_hook_installed || !g_server.valid())
+    return;
+  g_srv_base = g_server.ranges[0].lo;
+  uintptr_t slot = g_srv_base + 0xce1348; // R_386_JUMP_SLOT RandomSeed
+  if (!g_server.contains(slot))
+    return;
+  g_real_random_seed =
+      (void (*)(int))dlsym(RTLD_NEXT, "RandomSeed");
+  if (!g_real_random_seed)
+    g_real_random_seed = (void (*)(int))dlsym(RTLD_DEFAULT, "RandomSeed");
+  if (!g_real_random_seed) {
+    logf("seed hook: real RandomSeed not found");
+    return;
+  }
+  mprotect((void *)(slot & ~(uintptr_t)0xFFF), 0x1000,
+           PROT_READ | PROT_WRITE | PROT_EXEC);
+  *(uint32_t *)slot = (uint32_t)(uintptr_t)&hkdSrvRandomSeed;
+  g_seed_hook_installed = true;
+  logf("seed hook: server GOT %#lx -> %p (real %p)",
+       (unsigned long)slot, (void *)&hkdSrvRandomSeed,
+       (void *)g_real_random_seed);
+}
+
 static void do_move(int seq, float frametime) {
+  install_seed_hook();
   static bool g_echo_sent = false;
   if (!g_input || !g_net.ok())
     return;