From a69aaab6c4aeb6eebf3ebf06ea5886b2f7c1fb24 Mon Sep 17 00:00:00 2001
From: Gabriel Baraldi <baraldigabriel@gmail.com>
Date: Sat, 3 May 2025 12:33:46 -0300
Subject: [PATCH] Make build_id.lo more random (#58258)

This does not fix the underlying issue that can occur here which is a
collision of build_ids.lo between modules in IR decompression. Fixing
that requires a somewhat significant overhaul to the serialization of IR
(probably using the module identity as a key). This does mean we use a
lot more of the bits available here so it makes collisions a lot less
likely( they were already extremely rare) but hrtime does tend to only
use the lower bits of a 64 bit integer and this will hopefully add some
more randomness and make this even less likely
---
 src/module.c           |  3 ++-
 src/staticdata.c       |  6 +++++-
 src/staticdata_utils.c | 16 +++++++++++++++-
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/src/module.c b/src/module.c
index d39b7e377b2df..173f4dacf2769 100644
--- a/src/module.c
+++ b/src/module.c
@@ -24,7 +24,8 @@ JL_DLLEXPORT jl_module_t *jl_new_module_(jl_sym_t *name, jl_module_t *parent, ui
     m->istopmod = 0;
     m->uuid = uuid_zero;
     static unsigned int mcounter; // simple counter backup, in case hrtime is not incrementing
-    m->build_id.lo = jl_hrtime() + (++mcounter);
+    // TODO: this is used for ir decompression and is liable to hash collisions so use more of the bits
+    m->build_id.lo = bitmix(jl_hrtime() + (++mcounter), jl_rand());
     if (!m->build_id.lo)
         m->build_id.lo++; // build id 0 is invalid
     m->build_id.hi = ~(uint64_t)0;
diff --git a/src/staticdata.c b/src/staticdata.c
index 13284384e0485..ad62adb4ba178 100644
--- a/src/staticdata.c
+++ b/src/staticdata.c
@@ -3449,7 +3449,11 @@ static jl_value_t *jl_restore_package_image_from_stream(void* pkgimage_handle, i
 
             // No special processing of `new_specializations` is required because recaching handled it
             // Add roots to methods
-            jl_copy_roots(method_roots_list, jl_worklist_key((jl_array_t*)restored));
+            int failed = jl_copy_roots(method_roots_list, jl_worklist_key((jl_array_t*)restored));
+            if (failed != 0) {
+                jl_printf(JL_STDERR, "Error copying roots to methods from Module: %s\n", pkgname);
+                abort();
+            }
             // Insert method extensions
             jl_insert_methods(extext_methods);
             // Handle edges
diff --git a/src/staticdata_utils.c b/src/staticdata_utils.c
index 807fa2196ddf7..f08ca21017700 100644
--- a/src/staticdata_utils.c
+++ b/src/staticdata_utils.c
@@ -817,17 +817,31 @@ static void jl_insert_methods(jl_array_t *list)
     }
 }
 
-static void jl_copy_roots(jl_array_t *method_roots_list, uint64_t key)
+static int jl_copy_roots(jl_array_t *method_roots_list, uint64_t key)
 {
     size_t i, l = jl_array_len(method_roots_list);
+    int failed = 0;
     for (i = 0; i < l; i+=2) {
         jl_method_t *m = (jl_method_t*)jl_array_ptr_ref(method_roots_list, i);
         jl_array_t *roots = (jl_array_t*)jl_array_ptr_ref(method_roots_list, i+1);
         if (roots) {
             assert(jl_is_array(roots));
+            if (m->root_blocks) {
+                // check for key collision
+                uint64_t *blocks = (uint64_t*)jl_array_data(m->root_blocks);
+                size_t nx2 = jl_array_nrows(m->root_blocks);
+                for (size_t i = 0; i < nx2; i+=2) {
+                    if (blocks[i] == key) {
+                        // found duplicate block
+                        failed = -1;
+                    }
+                }
+            }
+
             jl_append_method_roots(m, key, roots);
         }
     }
+    return failed;
 }