Rollup merge of #143910 - ChrisDenton:no-symbolization, r=tgross35

Add experimental `backtrace-trace-only` std feature

This experimentally allows building std with backtrace but without symbolisation. It does not affect stable and requires build-std to use. This doesn't change the backtrace crate itself so relies on the optimizer to remove the unused parts.

Example usage:

```toml
# .cargo/config.toml
[unstable]
build-std = ["core", "alloc", "panic_unwind", "std"]
build-std-features = ["backtrace", "backtrace-trace-only", "panic-unwind"]
```

```toml
# Cargo.toml
[profile.release]
opt-level = 3
lto = "thin"
codegen-units = 1
```

Ideally we should split the backtrace feature into `backtrace-trace` and `backtrace-symbolize` (with the latter dependent on the former) because Cargo features tend to work better when they're positive rather than negative. But I'm keen for this experiment not to break existing users.

cc ``@joshtriplett``

library/std/Cargo.toml

@@ -92,6 +92,9 @@ backtrace = [
     'object/rustc-dep-of-std',
     'miniz_oxide/rustc-dep-of-std',
 ]
+# Disable symbolization in backtraces. For use with -Zbuild-std.
+# FIXME: Ideally this should be an additive backtrace-symbolization feature
+backtrace-trace-only = []
 
 panic-unwind = ["dep:panic_unwind"]
 compiler-builtins-c = ["alloc/compiler-builtins-c"]

library/std/src/sys/backtrace.rs

@@ -68,61 +68,67 @@ unsafe fn _print_fmt(fmt: &mut fmt::Formatter<'_>, print_fmt: PrintFmt) -> fmt::
                 return false;
             }
 
-            let mut hit = false;
-            backtrace_rs::resolve_frame_unsynchronized(frame, |symbol| {
-                hit = true;
+            if cfg!(feature = "backtrace-trace-only") {
+                const HEX_WIDTH: usize = 2 + 2 * size_of::<usize>();
+                let frame_ip = frame.ip();
+                res = writeln!(bt_fmt.formatter(), "{idx:4}: {frame_ip:HEX_WIDTH$?}");
+            } else {
+                let mut hit = false;
+                backtrace_rs::resolve_frame_unsynchronized(frame, |symbol| {
+                    hit = true;
 
-                // `__rust_end_short_backtrace` means we are done hiding symbols
-                // for now. Print until we see `__rust_begin_short_backtrace`.
-                if print_fmt == PrintFmt::Short {
-                    if let Some(sym) = symbol.name().and_then(|s| s.as_str()) {
-                        if sym.contains("__rust_end_short_backtrace") {
-                            print = true;
-                            return;
-                        }
-                        if print && sym.contains("__rust_begin_short_backtrace") {
-                            print = false;
-                            return;
-                        }
-                        if !print {
-                            omitted_count += 1;
+                    // `__rust_end_short_backtrace` means we are done hiding symbols
+                    // for now. Print until we see `__rust_begin_short_backtrace`.
+                    if print_fmt == PrintFmt::Short {
+                        if let Some(sym) = symbol.name().and_then(|s| s.as_str()) {
+                            if sym.contains("__rust_end_short_backtrace") {
+                                print = true;
+                                return;
+                            }
+                            if print && sym.contains("__rust_begin_short_backtrace") {
+                                print = false;
+                                return;
+                            }
+                            if !print {
+                                omitted_count += 1;
+                            }
                         }
                     }
-                }
 
-                if print {
-                    if omitted_count > 0 {
-                        debug_assert!(print_fmt == PrintFmt::Short);
-                        // only print the message between the middle of frames
-                        if !first_omit {
-                            let _ = writeln!(
-                                bt_fmt.formatter(),
-                                "      [... omitted {} frame{} ...]",
-                                omitted_count,
-                                if omitted_count > 1 { "s" } else { "" }
-                            );
+                    if print {
+                        if omitted_count > 0 {
+                            debug_assert!(print_fmt == PrintFmt::Short);
+                            // only print the message between the middle of frames
+                            if !first_omit {
+                                let _ = writeln!(
+                                    bt_fmt.formatter(),
+                                    "      [... omitted {} frame{} ...]",
+                                    omitted_count,
+                                    if omitted_count > 1 { "s" } else { "" }
+                                );
+                            }
+                            first_omit = false;
+                            omitted_count = 0;
                         }
-                        first_omit = false;
-                        omitted_count = 0;
+                        res = bt_fmt.frame().symbol(frame, symbol);
                     }
-                    res = bt_fmt.frame().symbol(frame, symbol);
+                });
+                #[cfg(target_os = "nto")]
+                if libc::__my_thread_exit as *mut libc::c_void == frame.ip() {
+                    if !hit && print {
+                        use crate::backtrace_rs::SymbolName;
+                        res = bt_fmt.frame().print_raw(
+                            frame.ip(),
+                            Some(SymbolName::new("__my_thread_exit".as_bytes())),
+                            None,
+                            None,
+                        );
+                    }
+                    return false;
                 }
-            });
-            #[cfg(target_os = "nto")]
-            if libc::__my_thread_exit as *mut libc::c_void == frame.ip() {
                 if !hit && print {
-                    use crate::backtrace_rs::SymbolName;
-                    res = bt_fmt.frame().print_raw(
-                        frame.ip(),
-                        Some(SymbolName::new("__my_thread_exit".as_bytes())),
-                        None,
-                        None,
-                    );
+                    res = bt_fmt.frame().print_raw(frame.ip(), None, None, None);
                 }
-                return false;
-            }
-            if !hit && print {
-                res = bt_fmt.frame().print_raw(frame.ip(), None, None, None);
             }
 
             idx += 1;

library/sysroot/Cargo.toml

@@ -20,6 +20,7 @@ test = { path = "../test", public = true }
 [features]
 default = ["std_detect_file_io", "std_detect_dlsym_getauxval", "panic-unwind"]
 backtrace = ["std/backtrace"]
+backtrace-trace-only = ["std/backtrace-trace-only"]
 compiler-builtins-c = ["std/compiler-builtins-c"]
 compiler-builtins-mem = ["std/compiler-builtins-mem"]
 compiler-builtins-no-asm = ["std/compiler-builtins-no-asm"]