From 4e817b9a26d538808101b57f99b7edbe590769db Mon Sep 17 00:00:00 2001
From: Brad Campbell <bradjc5@gmail.com>
Date: Mon, 9 Aug 2021 17:59:51 -0400
Subject: [PATCH 1/3] make padding an option for `elf_to_tbf()`

---
 src/main.rs | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 527fbae..e90cb39 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -106,6 +106,7 @@ fn main() {
             opt.protected_region_size,
             opt.permissions.to_vec(),
             minimum_tock_kernel_version,
+            true,
         )
         .unwrap();
         if opt.verbose {
@@ -148,6 +149,7 @@ fn elf_to_tbf<W: Write>(
     protected_region_size_arg: Option<u32>,
     permissions: Vec<(u32, u32)>,
     kernel_version: Option<(u16, u16)>,
+    trailing_padding: bool,
 ) -> io::Result<()> {
     let package_name = package_name.unwrap_or_default();
 
@@ -553,16 +555,25 @@ fn elf_to_tbf<W: Write>(
     // the relocation data length.
     binary_index += relocation_binary.len() + mem::size_of::<u32>();
 
-    // That is everything that we are going to include in our app binary. Now
-    // we need to pad the binary to a power of 2 in size, and make sure it is
-    // at least 512 bytes in size.
-    let post_content_pad = if binary_index.count_ones() > 1 {
-        let power2len = cmp::max(1 << (32 - (binary_index as u32).leading_zeros()), 512);
-        power2len - binary_index
+    // That is everything that we are going to include in our app binary.
+
+    let post_content_pad = if trailing_padding {
+        // If trailing padding is requested, we need to pad the binary to a
+        // power of 2 in size, and make sure it is at least 512 bytes in size.
+        let pad = if binary_index.count_ones() > 1 {
+            let power2len = cmp::max(1 << (32 - (binary_index as u32).leading_zeros()), 512);
+            power2len - binary_index
+        } else {
+            0
+        };
+        // Increment to include the padding.
+        binary_index += pad;
+        pad
     } else {
+        // No padding.
         0
     };
-    binary_index += post_content_pad;
+
     let total_size = binary_index;
 
     // Now set the total size of the app in the header.
@@ -580,7 +591,7 @@ fn elf_to_tbf<W: Write>(
     output.write_all(&rel_data_len)?;
     output.write_all(relocation_binary.as_ref())?;
 
-    // Pad to get a power of 2 sized flash app.
+    // Pad to get a power of 2 sized flash app, if requested.
     util::do_pad(output, post_content_pad as usize)?;
 
     Ok(())

From 68ecad60b2bb34a89dceca9603539e5f32667626 Mon Sep 17 00:00:00 2001
From: Brad Campbell <bradjc5@gmail.com>
Date: Mon, 9 Aug 2021 18:41:08 -0400
Subject: [PATCH 2/3] only add trailing padding to cortex-m apps

---
 src/main.rs | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/main.rs b/src/main.rs
index e90cb39..91843dd 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -91,6 +91,17 @@ fn main() {
             .open(tbf_path.clone())
             .unwrap();
 
+        // Adding padding to the end of cortex-m apps. Check for a cortex-m app
+        // because the start of the elf filename will start with "cortex".
+        //
+        // RISC-V apps do not need to be sized to power of two.
+        let add_trailing_padding = elf_path
+            .file_name()
+            .unwrap_or(std::ffi::OsStr::new(""))
+            .to_str()
+            .unwrap_or("")
+            .starts_with("cortex");
+
         // Do the conversion to a tock binary.
         if opt.verbose {
             println!("Creating {:?}", tbf_path);
@@ -106,7 +117,7 @@ fn main() {
             opt.protected_region_size,
             opt.permissions.to_vec(),
             minimum_tock_kernel_version,
-            true,
+            add_trailing_padding,
         )
         .unwrap();
         if opt.verbose {

From 98cb06449ffd2e9dc44e55caf7ad0d40038e8155 Mon Sep 17 00:00:00 2001
From: Brad Campbell <bradjc5@gmail.com>
Date: Tue, 10 Aug 2021 12:34:39 -0400
Subject: [PATCH 3/3] use elf header info to detect arm apps

---
 src/main.rs | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 91843dd..13f2aad 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -92,15 +92,12 @@ fn main() {
             .unwrap();
 
         // Adding padding to the end of cortex-m apps. Check for a cortex-m app
-        // because the start of the elf filename will start with "cortex".
+        // by inspecting the "machine" value in the elf header. 0x28 is ARM (see
+        // https://en.wikipedia.org/wiki/Executable_and_Linkable_Format#File_header
+        // for a list).
         //
         // RISC-V apps do not need to be sized to power of two.
-        let add_trailing_padding = elf_path
-            .file_name()
-            .unwrap_or(std::ffi::OsStr::new(""))
-            .to_str()
-            .unwrap_or("")
-            .starts_with("cortex");
+        let add_trailing_padding = elffile.ehdr.machine.0 == 0x28;
 
         // Do the conversion to a tock binary.
         if opt.verbose {