From caa6ba1a46afa1bc696adc5fe91ee992f9570c89 Mon Sep 17 00:00:00 2001
From: Yusuke Endoh <mame@ruby-lang.org>
Date: Wed, 4 Jun 2025 16:44:28 +0900
Subject: [PATCH] Make `rb_debug_inspector_backtrace_locations` return a raw
 backtrace

Previously, a user of the debug inspector API was supposed to use
`rb_debug_inspector_backtrace_locations` to get an array of
`Thread::Backtrace::Location`, and then used its index to get more
information from `rb_debug_inspector _frame_binding_get(index)`, etc.

However, `rb_debug_inspector_backtrace_locations` returned an array of
backtraces excluding rescue/ensure frames. On the other hand,
`rb_debug_inspector_frame_binding_get(index)` interprets index with
rescue/ensure frames. This led to inconsistency of the index, and it was
very difficult to correctly use the debug inspector API.

This is a minimal fix for the issue by making
`rb_debug_inspector_backtrace_locations` return a raw backtrace
including rescue/ensure frames.
---
 vm_backtrace.c | 39 +++++++++++++++++++++++++++++++--------
 1 file changed, 31 insertions(+), 8 deletions(-)

diff --git a/vm_backtrace.c b/vm_backtrace.c
index 26e0a6fb76..9046f4aa29 100644
--- a/vm_backtrace.c
+++ b/vm_backtrace.c
@@ -1493,9 +1493,8 @@ RUBY_SYMBOL_EXPORT_END
 struct rb_debug_inspector_struct {
     rb_execution_context_t *ec;
     rb_control_frame_t *cfp;
-    VALUE backtrace;
     VALUE contexts; /* [[klass, binding, iseq, cfp], ...] */
-    long backtrace_size;
+    VALUE raw_backtrace;
 };
 
 enum {
@@ -1504,18 +1503,22 @@ enum {
     CALLER_BINDING_BINDING,
     CALLER_BINDING_ISEQ,
     CALLER_BINDING_CFP,
+    CALLER_BINDING_LOC,
     CALLER_BINDING_DEPTH,
 };
 
 struct collect_caller_bindings_data {
     VALUE ary;
     const rb_execution_context_t *ec;
+    VALUE btobj;
+    rb_backtrace_t *bt;
 };
 
 static void
-collect_caller_bindings_init(void *arg, size_t size)
+collect_caller_bindings_init(void *arg, size_t num_frames)
 {
-    /* */
+    struct collect_caller_bindings_data *data = (struct collect_caller_bindings_data *)arg;
+    data->btobj = backtrace_alloc_capa(num_frames, &data->bt);
 }
 
 static VALUE
@@ -1553,6 +1556,14 @@ collect_caller_bindings_iseq(void *arg, const rb_control_frame_t *cfp)
     rb_ary_store(frame, CALLER_BINDING_BINDING, GC_GUARDED_PTR(cfp)); /* create later */
     rb_ary_store(frame, CALLER_BINDING_ISEQ, cfp->iseq ? (VALUE)cfp->iseq : Qnil);
     rb_ary_store(frame, CALLER_BINDING_CFP, GC_GUARDED_PTR(cfp));
+
+    rb_backtrace_location_t *loc = &data->bt->backtrace[data->bt->backtrace_size++];
+    RB_OBJ_WRITE(data->btobj, &loc->cme, rb_vm_frame_method_entry(cfp));
+    RB_OBJ_WRITE(data->btobj, &loc->iseq, cfp->iseq);
+    loc->pc = cfp->pc;
+    VALUE vloc = location_create(loc, (void *)data->btobj);
+    rb_ary_store(frame, CALLER_BINDING_LOC, vloc);
+
     rb_ary_store(frame, CALLER_BINDING_DEPTH, INT2FIX(frame_depth(data->ec, cfp)));
 
     rb_ary_push(data->ary, frame);
@@ -1569,6 +1580,14 @@ collect_caller_bindings_cfunc(void *arg, const rb_control_frame_t *cfp, ID mid)
     rb_ary_store(frame, CALLER_BINDING_BINDING, Qnil); /* not available */
     rb_ary_store(frame, CALLER_BINDING_ISEQ, Qnil); /* not available */
     rb_ary_store(frame, CALLER_BINDING_CFP, GC_GUARDED_PTR(cfp));
+
+    rb_backtrace_location_t *loc = &data->bt->backtrace[data->bt->backtrace_size++];
+    RB_OBJ_WRITE(data->btobj, &loc->cme, rb_vm_frame_method_entry(cfp));
+    loc->iseq = NULL;
+    loc->pc = NULL;
+    VALUE vloc = location_create(loc, (void *)data->btobj);
+    rb_ary_store(frame, CALLER_BINDING_LOC, vloc);
+
     rb_ary_store(frame, CALLER_BINDING_DEPTH, INT2FIX(frame_depth(data->ec, cfp)));
 
     rb_ary_push(data->ary, frame);
@@ -1617,15 +1636,19 @@ rb_debug_inspector_open(rb_debug_inspector_func_t func, void *data)
     rb_execution_context_t *ec = GET_EC();
     enum ruby_tag_type state;
     volatile VALUE MAYBE_UNUSED(result);
+    int i;
 
     /* escape all env to heap */
     rb_vm_stack_to_heap(ec);
 
     dbg_context.ec = ec;
     dbg_context.cfp = dbg_context.ec->cfp;
-    dbg_context.backtrace = rb_ec_backtrace_location_ary(ec, RUBY_BACKTRACE_START, RUBY_ALL_BACKTRACE_LINES, FALSE);
-    dbg_context.backtrace_size = RARRAY_LEN(dbg_context.backtrace);
     dbg_context.contexts = collect_caller_bindings(ec);
+    dbg_context.raw_backtrace = rb_ary_new();
+    for (i=0; i<RARRAY_LEN(dbg_context.contexts); i++) {
+        VALUE frame = rb_ary_entry(dbg_context.contexts, i);
+        rb_ary_push(dbg_context.raw_backtrace, rb_ary_entry(frame, CALLER_BINDING_LOC));
+    }
 
     EC_PUSH_TAG(ec);
     if ((state = EC_EXEC_TAG()) == TAG_NONE) {
@@ -1645,7 +1668,7 @@ rb_debug_inspector_open(rb_debug_inspector_func_t func, void *data)
 static VALUE
 frame_get(const rb_debug_inspector_t *dc, long index)
 {
-    if (index < 0 || index >= dc->backtrace_size) {
+    if (index < 0 || index >= RARRAY_LEN(dc->contexts)) {
         rb_raise(rb_eArgError, "no such frame");
     }
     return rb_ary_entry(dc->contexts, index);
@@ -1698,7 +1721,7 @@ rb_debug_inspector_current_depth(void)
 VALUE
 rb_debug_inspector_backtrace_locations(const rb_debug_inspector_t *dc)
 {
-    return dc->backtrace;
+    return dc->raw_backtrace;
 }
 
 static int