vm: improve context for early errors

Print "Before start of program" for errors that are raised before entering
main(), e.g. on module preloading failure.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

1 files changed, 3 insertions, 1 deletions

diff --git a/vm.c b/vm.c
index f7d2e09..7d60805 100644
--- a/vm.c
+++ b/vm.c
@@ -842,8 +842,10 @@ uc_vm_get_error_context(uc_vm *vm)
 
 	if (offset)
 		format_error_context(buf, frame->closure->function->source, stacktrace, offset);
+	else if (frame->ip != chunk->entries)
+		ucv_stringbuf_printf(buf, "At instruction %zu", (frame->ip - chunk->entries) - 1);
 	else
-		ucv_stringbuf_printf(buf, "At offset %zu", (frame->ip - chunk->entries) - 1);
+		ucv_stringbuf_append(buf, "At start of program");
 
 	ucv_object_add(ucv_array_get(stacktrace, 0), "context", ucv_stringbuf_finish(buf));