[feat] should document on how to support backtrace when size optimize

[loynoir]

Problem

When use size optimize config, backtrace is not working.

[profile.reproduce]
inherits = "release"

debug = false
strip = true

backtrace::Backtrace    0: <unknown>
   1: <unknown>
   2: <unknown>
   3: <unknown>
   4: __libc_start_main
   5: <unknown>

544K    bt

When use backtrace working config, size is much larger than size optimize config.

[profile.reproduce]
inherits = "release"

debug = true
strip = false

backtrace::Backtrace    0: bt::show_backtrace
             at /path/to/reproduce/src/bin/bt.rs:2:21
      bt::f4
             at /path/to/reproduce/src/bin/bt.rs:7:5
      bt::f3
             at /path/to/reproduce/src/bin/bt.rs:11:5
      bt::f2
             at /path/to/reproduce/src/bin/bt.rs:15:5
      bt::f1
             at /path/to/reproduce/src/bin/bt.rs:19:5
      bt::main
             at /path/to/reproduce/src/bin/bt.rs:23:5
   1: core::ops::function::FnOnce::call_once
             at /rustc/9b72238eb813e9d06e9e9d270168512fbffd7ee7/library/core/src/ops/function.rs:250:5
      std::sys::backtrace::__rust_begin_short_backtrace
             at /rustc/9b72238eb813e9d06e9e9d270168512fbffd7ee7/library/std/src/sys/backtrace.rs:154:18
   2: main
   3: <unknown>
   4: __libc_start_main
   5: _start

5.4M    bt

Proposed Solution

Should document on how to find a balance like something like below.

[profile.reproduce]
inherits = "release"

debug = false_but_keep_user_backtrace
strip = true_but_not_user_backtrace

backtrace::Backtrace    0: bt::show_backtrace
             at /path/to/reproduce/src/bin/bt.rs:2:21
      bt::f4
             at /path/to/reproduce/src/bin/bt.rs:7:5
      bt::f3
             at /path/to/reproduce/src/bin/bt.rs:11:5
      bt::f2
             at /path/to/reproduce/src/bin/bt.rs:15:5
      bt::f1
             at /path/to/reproduce/src/bin/bt.rs:19:5
      bt::main
             at /path/to/reproduce/src/bin/bt.rs:23:5
   **/rustc/xxx are not kept **
   **main, <unknown>, __libc_start_main, _start are not kept**

544K    bt

Notes

feat on backtrace side

rust-lang/backtrace-rs#675

[ChrisDenton]

There is already documentation, can you suggest an improvement? https://doc.rust-lang.org/cargo/reference/profiles.html

If you want to keep backtrace info intact then try:

debug = "line-tables-only"
strip = "debuginfo"

[loynoir]

Actually, f1 f2 f3 f4 are missing.

[profile.reproduce]
inherits = "release"

debug = "line-tables-only"
strip = "debuginfo"

backtrace::Backtrace    0: bt::main
   1: std::sys::backtrace::__rust_begin_short_backtrace
   2: main
   3: <unknown>
   4: __libc_start_main
   5: _start

620K    bt

[ChrisDenton]

Then try debug = "limited" as noted in the docs.

If a function is inlined then it essentially doesn't exist in the final binary. Therefore you need more debug information to reconstruct the full trace.

[ChrisDenton]

In any case, this isn't a Cargo issue. The debug field exposes the options rustc provides. If you think there's something more that rust could do here then file an issue on rust-lang,/rust. But removing debug information is always going to be in tension with providing a full backtrace.

[loynoir]

Emm, f1 f2 f3 f4 are still missing.

[profile.reproduce]
inherits = "release"

debug = "limited"
strip = "debuginfo"

backtrace::Backtrace    0: bt::main
   1: std::sys::backtrace::__rust_begin_short_backtrace
   2: main
   3: <unknown>
   4: __libc_start_main
   5: _start

620K    bt

[weihanglo]

In any case, this isn't a Cargo issue. The debug field exposes the options rustc provides. If you think there's something more that rust could do here then file an issue on rust-lang,/rust.

Agree with Chris.

Since the same issue has been opened twice, let's keep the discussion in one place. Close in favor of rust-lang/backtrace-rs#675.