Add '--set-addr' to defmt-print

CHANGELOG.md

@@ -509,6 +509,7 @@ Initial release
 
 ### [defmt-print-next]
 
+* [#985] Add `--set-addr` option to actively set the `_SEGGER_RTT` address
 * [#952] Support sending dtr on connection for serial port input
 * [#965] Also support `--log-format=online` or  `--log-format=default`
 * [#986] Bump MSRV to 1.81

print/Cargo.toml

@@ -16,6 +16,7 @@ version = "1.0.0"
 anyhow = "1"
 clap = { version = "4.0", features = ["derive", "env"] }
 defmt-decoder = { version = "=1.0.0", path = "../decoder" }
+goblin = "0.9"
 log = "0.4"
 notify = "8"
 tokio = { version = "1.38", features = ["full"] }

print/src/main.rs

@@ -13,10 +13,11 @@ use defmt_decoder::{
     },
     DecodeError, Frame, Locations, Table, DEFMT_VERSIONS,
 };
+use goblin::elf::Elf;
 use notify::{Config, Event, RecommendedWatcher, RecursiveMode, Watcher};
 use tokio::{
     fs,
-    io::{self, AsyncReadExt, Stdin},
+    io::{self, AsyncReadExt, AsyncWriteExt, Stdin},
     net::TcpStream,
     select,
     sync::mpsc::Receiver,
@@ -27,30 +28,43 @@ use tokio_serial::{SerialPort, SerialPortBuilderExt, SerialStream};
 #[derive(Parser, Clone)]
 #[command(name = "defmt-print")]
 struct Opts {
+    /// The firmware running on the device being logged
     #[arg(short, required = true, conflicts_with("version"))]
     elf: Option<PathBuf>,
 
+    /// Emit logs in JSON format
     #[arg(long)]
     json: bool,
 
+    /// A format string for target-generated logs
     #[arg(long)]
     log_format: Option<String>,
 
+    /// A format string for host-generated logs
     #[arg(long)]
     host_log_format: Option<String>,
 
+    /// Tell Segger J-Link what the RTT address is
+    #[arg(long)]
+    set_addr: bool,
+
+    /// Log any malformed defmt frames that are being skipped
     #[arg(long)]
     show_skipped_frames: bool,
 
+    /// Print extra detail
     #[arg(short, long)]
     verbose: bool,
 
+    /// Print the version number, and quit
     #[arg(short = 'V', long)]
     version: bool,
 
+    /// Reload the ELF file when it changes
     #[arg(short, long)]
     watch_elf: bool,
 
+    /// Which operation to perform
     #[command(subcommand)]
     command: Option<Command>,
 }
@@ -59,14 +73,15 @@ struct Opts {
 enum Command {
     /// Read defmt frames from stdin (default)
     Stdin,
-    /// Read defmt frames from tcp
+    /// Read defmt frames from a TCP server
     Tcp {
         #[arg(long, env = "RTT_HOST", default_value = "localhost")]
         host: String,
 
         #[arg(long, env = "RTT_PORT", default_value_t = 19021)]
         port: u16,
     },
+    /// Read defmt frames from a serial port
     Serial {
         #[arg(long, env = "SERIAL_PORT", default_value = "/dev/ttyUSB0")]
         path: PathBuf,
@@ -106,6 +121,27 @@ impl Source {
         Ok(Source::Serial(ser))
     }
 
+    async fn set_rtt_addr(&mut self, elf_bytes: &[u8]) -> anyhow::Result<()> {
+        let Source::Tcp(tcpstream) = self else {
+            return Ok(());
+        };
+
+        let elf = Elf::parse(elf_bytes)?;
+        let rtt_symbol = elf
+            .syms
+            .iter()
+            .find(|sym| elf.strtab.get_at(sym.st_name) == Some("_SEGGER_RTT"))
+            .ok_or_else(|| anyhow!("Symbol '_SEGGER_RTT' not found in ELF file"))?;
+
+        let cmd = format!(
+            "$$SEGGER_TELNET_ConfigStr=SetRTTAddr;{:#x}$$",
+            rtt_symbol.st_value
+        );
+        tcpstream.write_all(cmd.as_bytes()).await?;
+
+        Ok(())
+    }
+
     async fn read(&mut self, buf: &mut [u8]) -> anyhow::Result<(usize, bool)> {
         match self {
             Source::Stdin(stdin) => {
@@ -186,6 +222,7 @@ async fn run(opts: Opts, source: &mut Source) -> anyhow::Result<()> {
         json,
         log_format,
         host_log_format,
+        set_addr,
         show_skipped_frames,
         verbose,
         ..
@@ -196,6 +233,11 @@ async fn run(opts: Opts, source: &mut Source) -> anyhow::Result<()> {
     let table = Table::parse(&bytes)?.ok_or_else(|| anyhow!(".defmt data not found"))?;
     let locs = table.get_locations(&bytes)?;
 
+    if set_addr {
+        // Using Segger RTT server, set the _SEGGER_RTT address actively.
+        source.set_rtt_addr(&bytes).await?;
+    }
+
     // check if the locations info contains all the indicies
     let locs = if table.indices().all(|idx| locs.contains_key(&(idx as u64))) {
         Some(locs)