[sw/host] Update text end address in signer tool.

Update the signer tool to look for the .shutdown section as well as the
.text section when calculating the end address of executable code.

Signed-off-by: Miguel Osorio <miguelosorio@google.com>

sw/host/rom_ext_image_tools/signer/Cargo.toml

@@ -27,6 +27,7 @@ debug = true
 anyhow = "1.0.40"
 object = "0.25.3"
 rom_ext_image = { path = "image" }
+thiserror = "1.0.24"
 zerocopy = "0.5.0"
 
 [dependencies.mundane]

sw/host/rom_ext_image_tools/signer/src/main.rs

@@ -105,12 +105,17 @@ fn update_image_manifest(
             addr.checked_sub(manifest_addr).context("Overflow")?
         },
         code_end: {
-            let text = elf
-                .section_by_name(".text")
-                .context("Could not find the `.text` section.")?;
+            // TODO: Consider requiring all binaries signed by this tool to have a .shutdown section.
+            let section = elf
+                .section_by_name(".shutdown")
+                .or(elf.section_by_name(".text"))
+                .context(
+                    "Could not find the `.shutdown` or `.text` section.",
+                )?;
             let addr = u32::try_from(
-                text.address()
-                    .checked_add(text.size())
+                section
+                    .address()
+                    .checked_add(section.size())
                     .context("Overflow")?,
             )?;
             addr.checked_sub(manifest_addr).context("Overflow")?
@@ -171,7 +176,8 @@ fn update_image_manifest(
         "`entry_point` is outside the code region."
     );
     ensure!(
-        (manifest::MANIFEST_LENGTH_FIELD_MIN..=manifest::MANIFEST_LENGTH_FIELD_MAX)
+        (manifest::MANIFEST_LENGTH_FIELD_MIN
+            ..=manifest::MANIFEST_LENGTH_FIELD_MAX)
             .contains(&image.manifest.length),
         "`length` is outside the allowed range."
     );