libdrgn: stack_trace: fix source info without .debug_aranges

dwfl_module_getsrc() relies on .debug_aranges to find the CU containing
the PC. If the module has a missing or incomplete .debug_aranges, it
fails. This lookup is actually redundant since we already found the CU
when we unwound the stack. Use the libdw helpers that take the CU DIE
instead to avoid this. We also need to save the CU for frames where we
found it but couldn't find the subprogram (typically assembly files).

Signed-off-by: Omar Sandoval <osandov@osandov.com>

libdrgn/stack_trace.c

@@ -291,21 +291,38 @@ drgn_stack_frame_source(struct drgn_stack_trace *trace, size_t frame,
 				*column_ret = value;
 		}
 		return filename;
-	} else {
+	} else if (trace->frames[frame].num_scopes > 0) {
 		struct drgn_register_state *regs = trace->frames[frame].regs;
 		Dwfl_Module *dwfl_module =
 			regs->module ? regs->module->dwfl_module : NULL;
 		if (!dwfl_module)
 			return NULL;
+
 		struct optional_uint64 pc = drgn_register_state_get_pc(regs);
 		if (!pc.has_value)
 			return NULL;
-		pc.value -= !regs->interrupted;
-		Dwfl_Line *line = dwfl_module_getsrc(dwfl_module, pc.value);
+		Dwarf_Addr bias;
+		if (!dwfl_module_getdwarf(dwfl_module, &bias))
+			return NULL;
+		pc.value = pc.value - bias - !regs->interrupted;
+
+		Dwarf_Die *scopes = trace->frames[frame].scopes;
+		size_t num_scopes = trace->frames[frame].num_scopes;
+		Dwarf_Die cu_die;
+		if (!dwarf_cu_die(scopes[num_scopes - 1].cu, &cu_die, NULL,
+				  NULL, NULL, NULL, NULL, NULL))
+			return NULL;
+
+		Dwarf_Line *line = dwarf_getsrc_die(&cu_die, pc.value);
 		if (!line)
 			return NULL;
-		return dwfl_lineinfo(line, NULL, line_ret, column_ret, NULL,
-				     NULL);
+		if (line_ret)
+			dwarf_lineno(line, line_ret);
+		if (column_ret)
+			dwarf_linecol(line, column_ret);
+		return dwarf_linesrc(line, NULL, NULL);
+	} else {
+		return NULL;
 	}
 }
 
@@ -359,7 +376,7 @@ drgn_stack_frame_find_object(struct drgn_stack_trace *trace, size_t frame_i,
 	struct drgn_error *err;
 	struct drgn_stack_frame *frame = &trace->frames[frame_i];
 
-	if (frame->num_scopes == 0)
+	if (frame->function_scope >= frame->num_scopes)
 		goto not_found;
 
 	Dwarf_Die die, type_die;
@@ -811,11 +828,25 @@ drgn_stack_trace_add_frames(struct drgn_stack_trace **trace,
 
 	/*
 	 * We didn't find a matching DW_TAG_subprogram. Free any matching
-	 * DW_TAG_inlined_subroutine frames we found and add a scopeless frame.
+	 * DW_TAG_inlined_subroutine frames we found.
 	 */
 	for (size_t i = orig_num_frames; i < (*trace)->num_frames; i++)
 		free((*trace)->frames[i].scopes);
 	(*trace)->num_frames = orig_num_frames;
+	/* If we at least found the unit DIE, keep it. */
+	if (num_scopes > 0) {
+		Dwarf_Die *frame_scopes;
+		if (!(frame_scopes = realloc(scopes, sizeof(scopes[0]))))
+			frame_scopes = scopes;
+		err = drgn_stack_trace_append_frame(trace, trace_capacity, regs,
+						    frame_scopes, 1, 1);
+		if (err) {
+			free(frame_scopes);
+			goto out;
+		}
+		return NULL;
+	}
+	/* Otherwise, add a scopeless frame. */
 	err = drgn_stack_trace_append_frame(trace, trace_capacity, regs, NULL,
 					    0, 0);
 out_scopes: