make DEFAULT_MAX_BACKTRACE_LEN configurable

src/main.rs

@@ -102,6 +102,10 @@ struct Opts {
     #[structopt(long)]
     force_backtrace: bool,
 
+    /// Configure the number of lines to print before a backtrace gets cut off
+    #[structopt(long)]
+    max_backtrace_len: Option<u32>,
+
     /// Arguments passed after the ELF file path are discarded
     #[structopt(name = "REST")]
     _rest: Vec<String>,
@@ -145,6 +149,10 @@ fn notmain() -> anyhow::Result<i32> {
     }
 
     let force_backtrace = opts.force_backtrace;
+    let max_backtrace_len = match opts.max_backtrace_len {
+        Some(len) => len,
+        None => DEFAULT_MAX_BACKTRACE_LEN,
+    };
     let elf_path = opts.elf.as_deref().unwrap();
     let chip = opts.chip.as_deref().unwrap();
     let bytes = fs::read(elf_path)?;
@@ -561,7 +569,7 @@ fn notmain() -> anyhow::Result<i32> {
         &current_dir,
         // TODO any other cases in which we should force a backtrace?
         force_backtrace || canary_touched,
-        DEFAULT_MAX_BACKTRACE_LEN,
+        max_backtrace_len,
     )?;
 
     core.reset_and_halt(TIMEOUT)?;
@@ -855,8 +863,8 @@ fn construct_backtrace(
         }
 
         if frame_index >= max_backtrace_len {
-            // TODO add hint here on how to extend the length
-            log::warn!("Maximum backtrace length of {:?} reached; cutting off the rest",
+            log::warn!("Maximum backtrace length of {:?} reached; cutting off the rest
+               note: re-run with `--max-backtrace-len=<your maximum>` to extend this limit",
                      max_backtrace_len);
             return Ok(top_exception);
         }