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Fix GC compaction crash when using local variables in eval

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If we have local variables outside of the eval, the local variables names
are IDs. We convert these IDs to char * using rb_id2name. However, these
char * are actually Ruby strings, which may be embedded. This means that
it is not safe to rb_id2name and call any potential GC entrypoints because
if a GC compaction runs, the embedded string may move and the pointer will
change.

For example, if you compile with `-DRGENGC_CHECK_MODE=1`, then the following
script will crash:

    GC.auto_compact = :empty
    GC.stress = true

    o = Object.new

    eval("def o.m(k: 0) k end")

The crash message is:

    test.rb:6: [BUG] Local with constant_id 1 does not exist
    ruby 3.4.0dev (2024-12-17T18:34:57Z prism-local-compac.. 434346726c) +PRISM [arm64-darwin24]

    -- C level backtrace information -------------------------------------------
    miniruby(rb_print_backtrace+0x24) [0x10312fec4] vm_dump.c:823
    miniruby(rb_print_backtrace) (null):0
    miniruby(rb_vm_bugreport+0x2d4) [0x1031301b8] vm_dump.c:1155
    miniruby(rb_bug_without_die_internal+0xa8) [0x102dd6a94] error.c:1097
    miniruby(rb_bug+0x28) [0x102dd6b00] error.c:1115
    miniruby(pm_lookup_local_index+0xec) [0x102d61e4c] prism_compile.c:1237
    miniruby(pm_compile_node+0x45d0) [0x102d252f4] prism_compile.c:9334
    miniruby(pm_compile_node+0x1864) [0x102d22588] prism_compile.c:8650
    miniruby(pm_compile_node+0x65ec) [0x102d27310] prism_compile.c:9897
    miniruby(pm_compile_scope_node+0x3008) [0x102d77bcc] prism_compile.c:6584
    miniruby(pm_compile_node+0x5ec4) [0x102d26be8] prism_compile.c:9768
    miniruby(pm_iseq_compile_node+0xac) [0x102d20bf0] prism_compile.c:10069
    miniruby(pm_iseq_new_with_opt_try+0x2c) [0x102e7d088] iseq.c:1029
    miniruby(rb_protect+0x108) [0x102dea9bc] eval.c:1033
    miniruby(pm_iseq_new_with_opt+0x264) [0x102e7c444] iseq.c:1082
    miniruby(pm_iseq_new_eval+0xec) [0x102e7c8e0] iseq.c:961
    miniruby(pm_eval_make_iseq+0x594) [0x1031209cc] vm_eval.c:1770
    miniruby(eval_make_iseq+0x54) [0x103120068] vm_eval.c:1799
This commit is contained in:
Peter Zhu 2024-12-17 14:14:36 -05:00 committed by Kevin Newton
parent 85f3ed8cdb
commit e23a60b929
Notes: git 2024-12-20 13:25:11 +00:00 
Merged: https://github.com/ruby/ruby/pull/12374
2 changed files with 26 additions and 2 deletions
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15
test/ruby/test_eval.rb
View File

@ -636,4 +636,19 @@ class TestEval < Test::Unit::TestCase
end
end;
end
def test_outer_local_variable_under_gc_compact_stress
omit "compaction is not supported on this platform" unless GC.respond_to?(:compact)
assert_separately([], <<~RUBY)
o = Object.new
def o.m = 1
GC.verify_compaction_references(expand_heap: true, toward: :empty)
EnvUtil.under_gc_compact_stress do
assert_equal(1, eval("o.m"))
end
RUBY
end
end

13
vm_eval.c
View File

@ -1700,7 +1700,8 @@ pm_eval_make_iseq(VALUE src, VALUE fname, int line,
ID local = ISEQ_BODY(iseq)->local_table[local_index];
if (rb_is_local_id(local)) {
const char *name = rb_id2name(local);
VALUE name_obj = rb_id2str(local);
const char *name = RSTRING_PTR(name_obj);
size_t length = strlen(name);
// Explicitly skip numbered parameters. These should not be sent
@ -1709,7 +1710,15 @@ pm_eval_make_iseq(VALUE src, VALUE fname, int line,
continue;
}
pm_string_constant_init(scope_local, name, length);
/* We need to duplicate the string because the Ruby string may
* be embedded so compaction could move the string and the pointer
* will change. */
char *name_dup = xmalloc(length + 1);
strlcpy(name_dup, name, length + 1);
RB_GC_GUARD(name_obj);
pm_string_owned_init(scope_local, (uint8_t *)name_dup, length);
}
}