Factor out common backtrace frame truncating code

Author: cramertj

src/capture.rs

@@ -385,7 +385,13 @@ cfg_if::cfg_if! {
 
 impl fmt::Debug for Backtrace {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
-        fmt_backtrace(self, fmt)
+        fmt.write_str("stack backtrace:\n")?;
+        let frames = if fmt.alternate() {
+            &self.frames[..]
+        } else {
+            &self.frames[self.actual_start_index..]
+        };
+        fmt_backtrace(frames, fmt)
     }
 }
 

src/capture/default_backtrace_fmt.rs

@@ -1,17 +1,9 @@
-use crate::Backtrace;
+use super::BacktraceFrame;
 use std::ffi::c_void;
 use std::fmt;
 
-pub(super) fn fmt_backtrace(bt: &Backtrace, fmt: &mut fmt::Formatter) -> fmt::Result {
-    write!(fmt, "stack backtrace:")?;
-
-    let iter = if fmt.alternate() {
-        bt.frames.iter()
-    } else {
-        bt.frames[bt.actual_start_index..].iter()
-    };
-
-    for (idx, frame) in iter.enumerate() {
+pub(super) fn fmt_backtrace(frames: &[BacktraceFrame], fmt: &mut fmt::Formatter) -> fmt::Result {
+    for (idx, frame) in frames.iter().enumerate() {
         // To reduce TCB size in Sgx enclave, we do not want to implement symbol resolution functionality.
         // Rather, we can print the offset of the address here, which could be later mapped to
         // correct function.

src/capture/fuchsia_backtrace_fmt.rs

@@ -1,25 +1,17 @@
-use crate::Backtrace;
+use super::BacktraceFrame;
 use libc::c_void;
 use std::fmt;
 
-pub(super) fn fmt_backtrace(bt: &Backtrace, fmt: &mut fmt::Formatter) -> fmt::Result {
-    fmt.write_str("stack backtrace:\n")?;
-
+pub(super) fn fmt_backtrace(frames: &[BacktraceFrame], fmt: &mut fmt::Formatter) -> fmt::Result {
     // Print the DSO context to tell the logger where our libs are loaded into memory.
     let mut dso_cx = vec![];
     fuchsia_backtrace::print_dso_context(&mut dso_cx).map_err(|_| fmt::Error)?;
     if let Ok(s) = std::string::String::from_utf8(dso_cx) {
         fmt.write_str(&s)?;
     }
 
-    let iter = if fmt.alternate() {
-        bt.frames.iter()
-    } else {
-        bt.frames[bt.actual_start_index..].iter()
-    };
-
     // Print the addresses of the backtrace frames
-    for (idx, frame) in iter.enumerate() {
+    for (idx, frame) in frames.iter().enumerate() {
         let ip: *mut c_void = frame.ip();
         fmt.write_str("{{{bt:")?;
         write!(fmt, "{}:{:?}", idx, ip)?;