std: Switch from libbacktrace to gimli

This commit is a proof-of-concept for switching the standard library's
backtrace symbolication mechanism on most platforms from libbacktrace to
gimli. The standard library's support for `RUST_BACKTRACE=1` requires
in-process parsing of object files and DWARF debug information to
interpret it and print the filename/line number of stack frames as part
of a backtrace.

Historically this support in the standard library has come from a
library called "libbacktrace". The libbacktrace library seems to have
been extracted from gcc at some point and is written in C. We've had a
lot of issues with libbacktrace over time, unfortunately, though. The
library does not appear to be actively maintained since we've had
patches sit for months-to-years without comments. We have discovered a
good number of soundness issues with the library itself, both when
parsing valid DWARF as well as invalid DWARF. This is enough of an issue
that the libs team has previously decided that we cannot feed untrusted
inputs to libbacktrace. This also doesn't take into account the
portability of libbacktrace which has been difficult to manage and
maintain over time. While possible there are lots of exceptions and it's
the main C dependency of the standard library right now.

For years it's been the desire to switch over to a Rust-based solution
for symbolicating backtraces. It's been assumed that we'll be using the
Gimli family of crates for this purpose, which are targeted at safely
and efficiently parsing DWARF debug information. I've been working
recently to shore up the Gimli support in the `backtrace` crate. As of a
few weeks ago the `backtrace` crate, by default, uses Gimli when loaded
from crates.io. This transition has gone well enough that I figured it
was time to start talking seriously about this change to the standard
library.

This commit is a preview of what's probably the best way to integrate
the `backtrace` crate into the standard library with the Gimli feature
turned on. While today it's used as a crates.io dependency, this commit
switches the `backtrace` crate to a submodule of this repository which
will need to be updated manually. This is not done lightly, but is
thought to be the best solution. The primary reason for this is that the
`backtrace` crate needs to do some pretty nontrivial filesystem
interactions to locate debug information. Working without `std::fs` is
not an option, and while it might be possible to do some sort of
trait-based solution when prototyped it was found to be too unergonomic.
Using a submodule allows the `backtrace` crate to build as a submodule
of the `std` crate itself, enabling it to use `std::fs` and such.

Otherwise this adds new dependencies to the standard library. This step
requires extra attention because this means that these crates are now
going to be included with all Rust programs by default. It's important
to note, however, that we're already shipping libbacktrace with all Rust
programs by default and it has a bunch of C code implementing all of
this internally anyway, so we're basically already switching
already-shipping functionality to Rust from C.

* `object` - this crate is used to parse object file headers and
  contents. Very low-level support is used from this crate and almost
  all of it is disabled. Largely we're just using struct definitions as
  well as convenience methods internally to read bytes and such.

* `addr2line` - this is the main meat of the implementation for
  symbolication. This crate depends on `gimli` for DWARF parsing and
  then provides interfaces needed by the `backtrace` crate to turn an
  address into a filename / line number. This crate is actually pretty
  small (fits in a single file almost!) and mirrors most of what
  `dwarf.c` does for libbacktrace.

* `miniz_oxide` - the libbacktrace crate transparently handles
  compressed debug information which is compressed with zlib. This crate
  is used to decompress compressed debug sections.

* `gimli` - not actually used directly, but a dependency of `addr2line`.

* `adler32`- not used directly either, but a dependency of
  `miniz_oxide`.

The goal of this change is to improve the safety of backtrace
symbolication in the standard library, especially in the face of
possibly malformed DWARF debug information. Even to this day we're still
seeing segfaults in libbacktrace which could possibly become security
vulnerabilities. This change should almost entirely eliminate this
possibility whilc also paving the way forward to adding more features
like split debug information.

Some references for those interested are:

* Original addition of libbacktrace - #12602
* OOM with libbacktrace - #24231
* Backtrace failure due to use of uninitialized value - #28447
* Possibility to feed untrusted data to libbacktrace - #21889
* Soundness fix for libbacktrace - #33729
* Crash in libbacktrace - #39468
* Support for macOS, never merged - ianlancetaylor/libbacktrace#2
* Performance issues with libbacktrace - #29293, #37477
* Update procedure is quite complicated due to how many patches we
  need to carry - #50955
* Libbacktrace doesn't work on MinGW with dynamic libs - #71060
* Segfault in libbacktrace on macOS - #71397

Switching to Rust will not make us immune to all of these issues. The
crashes are expected to go away, but correctness and performance may
still have bugs arise. The gimli and `backtrace` crates, however, are
actively maintained unlike libbacktrace, so this should enable us to at
least efficiently apply fixes as situations come up.

13 files changed, 107 insertions, 55 deletions

diff --git a/.gitmodules b/.gitmodules
index 5c0ab737f63..b914b7d6fa1 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -44,3 +44,6 @@
 [submodule "src/tools/rust-analyzer"]
 	path = src/tools/rust-analyzer
 	url = https://github.com/rust-analyzer/rust-analyzer.git
+[submodule "src/backtrace"]
+	path = src/backtrace
+	url = https://github.com/rust-lang/backtrace-rs.git
diff --git a/Cargo.lock b/Cargo.lock
index 28ff6b3b1eb..6f27619258a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1,10 +1,26 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
 [[package]]
-name = "adler32"
-version = "1.0.3"
+name = "addr2line"
+version = "0.13.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7e522997b529f05601e05166c07ed17789691f562762c7f3b987263d2dedee5c"
+checksum = "1b6a2d3371669ab3ca9797670853d61402b03d0b4b9ebf33d677dfa720203072"
+dependencies = [
+ "compiler_builtins",
+ "gimli",
+ "rustc-std-workspace-alloc",
+ "rustc-std-workspace-core",
+]
+
+[[package]]
+name = "adler"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ccc9a9dd069569f212bc4330af9f17c4afb5e8ce185e83dbb14f1349dda18b10"
+dependencies = [
+ "compiler_builtins",
+ "rustc-std-workspace-core",
+]
 
 [[package]]
 name = "aho-corasick"
@@ -125,28 +141,14 @@ checksum = "f8aac770f1885fd7e387acedd76065302551364496e46b3dd00860b2f8359b9d"
 
 [[package]]
 name = "backtrace"
-version = "0.3.46"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b1e692897359247cc6bb902933361652380af0f1b7651ae5c5013407f30e109e"
+version = "0.3.50"
 dependencies = [
- "backtrace-sys",
+ "addr2line",
  "cfg-if",
- "compiler_builtins",
  "libc",
+ "miniz_oxide",
+ "object",
  "rustc-demangle",
- "rustc-std-workspace-core",
-]
-
-[[package]]
-name = "backtrace-sys"
-version = "0.1.37"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "18fbebbe1c9d1f383a9cc7e8ccdb471b91c8d024ee9c2ca5b5346121fe8b4399"
-dependencies = [
- "cc",
- "compiler_builtins",
- "libc",
- "rustc-std-workspace-core",
 ]
 
 [[package]]
@@ -688,9 +690,9 @@ dependencies = [
 
 [[package]]
 name = "crc32fast"
-version = "1.1.2"
+version = "1.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e91d5240c6975ef33aeb5f148f35275c25eda8e8a5f95abe421978b05b8bf192"
+checksum = "ba125de2af0df55319f41944744ad91c71113bf74a4646efff39afe1f6842db1"
 dependencies = [
  "cfg-if",
 ]
@@ -1023,9 +1025,9 @@ checksum = "37ab347416e802de484e4d03c7316c48f1ecb56574dfd4a46a80f173ce1de04d"
 
 [[package]]
 name = "flate2"
-version = "1.0.12"
+version = "1.0.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ad3c5233c9a940c8719031b423d7e6c16af66e031cb0420b0896f5245bf181d3"
+checksum = "68c90b0fc46cf89d227cc78b40e494ff81287a92dd07631e5af0d06fe3cf885e"
 dependencies = [
  "cfg-if",
  "crc32fast",
@@ -1160,6 +1162,17 @@ dependencies = [
 ]
 
 [[package]]
+name = "gimli"
+version = "0.22.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aaf91faf136cb47367fa430cd46e37a788775e7fa104f8b4bcb3861dc389b724"
+dependencies = [
+ "compiler_builtins",
+ "rustc-std-workspace-alloc",
+ "rustc-std-workspace-core",
+]
+
+[[package]]
 name = "git2"
 version = "0.13.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1819,11 +1832,14 @@ dependencies = [
 
 [[package]]
 name = "miniz_oxide"
-version = "0.3.5"
+version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6f3f74f726ae935c3f514300cc6773a0c9492abc5e972d42ba0c0ebb88757625"
+checksum = "be0f75932c1f6cfae3c04000e40114adf955636e19040f9c0a2c380702aa1c7f"
 dependencies = [
- "adler32",
+ "adler",
+ "compiler_builtins",
+ "rustc-std-workspace-alloc",
+ "rustc-std-workspace-core",
 ]
 
 [[package]]
@@ -1956,6 +1972,17 @@ dependencies = [
 ]
 
 [[package]]
+name = "object"
+version = "0.20.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1ab52be62400ca80aa00285d25253d7f7c437b7375c4de678f5405d3afe82ca5"
+dependencies = [
+ "compiler_builtins",
+ "rustc-std-workspace-alloc",
+ "rustc-std-workspace-core",
+]
+
+[[package]]
 name = "once_cell"
 version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -4332,8 +4359,8 @@ dependencies = [
 name = "std"
 version = "0.0.0"
 dependencies = [
+ "addr2line",
  "alloc",
- "backtrace",
  "cfg-if",
  "compiler_builtins",
  "core",
@@ -4342,10 +4369,13 @@ dependencies = [
  "hashbrown",
  "hermit-abi",
  "libc",
+ "miniz_oxide",
+ "object",
  "panic_abort",
  "panic_unwind",
  "profiler_builtins",
  "rand 0.7.3",
+ "rustc-demangle",
  "unwind",
  "wasi",
 ]
diff --git a/Cargo.toml b/Cargo.toml
index be15e50e2bc..4270cabec15 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -79,5 +79,11 @@ rustc-std-workspace-core = { path = 'src/tools/rustc-std-workspace-core' }
 rustc-std-workspace-alloc = { path = 'src/tools/rustc-std-workspace-alloc' }
 rustc-std-workspace-std = { path = 'src/tools/rustc-std-workspace-std' }
 
+# This crate's integration with libstd is a bit wonky, so we use a submodule
+# instead of a crates.io dependency. Make sure everything else in the repo is
+# also using the submodule, however, so we can avoid duplicate copies of the
+# source code for this crate.
+backtrace = { path = "src/backtrace" }
+
 [patch."https://github.com/rust-lang/rust-clippy"]
 clippy_lints = { path = "src/tools/clippy/clippy_lints" }
diff --git a/rustfmt.toml b/rustfmt.toml
index c76a75fa07b..b16aecc463c 100644
--- a/rustfmt.toml
+++ b/rustfmt.toml
@@ -30,6 +30,7 @@ ignore = [
     "src/tools/rust-analyzer",
     "src/tools/rust-installer",
     "src/tools/rustfmt",
+    "src/backtrace",
 
     # We do not format this file as it is externally sourced and auto-generated.
     "src/libstd/sys/cloudabi/abi/cloudabi.rs",
diff --git a/src/backtrace b/src/backtrace
new file mode 160000
+Subproject 8f89434446f72f27f8145d8bbc1a302c6ef29d1
diff --git a/src/libstd/Cargo.toml b/src/libstd/Cargo.toml
index 29893bd12f1..136db6d5d32 100644
--- a/src/libstd/Cargo.toml
+++ b/src/libstd/Cargo.toml
@@ -25,11 +25,15 @@ profiler_builtins = { path = "../libprofiler_builtins", optional = true }
 unwind = { path = "../libunwind" }
 hashbrown = { version = "0.6.2", default-features = false, features = ['rustc-dep-of-std'] }
 
-[dependencies.backtrace_rs]
-package = "backtrace"
-version = "0.3.46"
-default-features = false # without the libstd `backtrace` feature, stub out everything
-features = [ "rustc-dep-of-std" ] # enable build support for integrating into libstd
+# Dependencies of the `backtrace` crate
+addr2line = { version = "0.13.0", optional = true, default-features = false }
+rustc-demangle = { version = "0.1.4", optional = true }
+miniz_oxide = { version = "0.4.0", optional = true, default-features = false }
+[dependencies.object]
+version = "0.20"
+optional = true
+default-features = false
+features = ['read_core', 'elf', 'macho', 'pe']
 
 [dev-dependencies]
 rand = "0.7"
@@ -48,11 +52,13 @@ wasi = { version = "0.9.0", features = ['rustc-dep-of-std'], default-features =
 
 [features]
 backtrace = [
-  "backtrace_rs/dbghelp",          # backtrace/symbolize on MSVC
-  "backtrace_rs/libbacktrace",     # symbolize on most platforms
-  "backtrace_rs/libunwind",        # backtrace on most platforms
-  "backtrace_rs/dladdr",           # symbolize on platforms w/o libbacktrace
+  "gimli-symbolize",
+  'addr2line/rustc-dep-of-std',
+  'object/rustc-dep-of-std',
+  'rustc-demangle/rustc-dep-of-std',
+  'miniz_oxide/rustc-dep-of-std',
 ]
+gimli-symbolize = []
 
 panic-unwind = ["panic_unwind"]
 profiler = ["profiler_builtins"]
diff --git a/src/libstd/backtrace.rs b/src/libstd/backtrace.rs
index e10d466030f..e65775c1ced 100644
--- a/src/libstd/backtrace.rs
+++ b/src/libstd/backtrace.rs
@@ -91,6 +91,7 @@
 // `Backtrace`, but that's a relatively small price to pay relative to capturing
 // a backtrace or actually symbolizing it.
 
+use crate::backtrace_rs::{self, BytesOrWideString};
 use crate::env;
 use crate::ffi::c_void;
 use crate::fmt;
@@ -98,8 +99,6 @@ use crate::sync::atomic::{AtomicUsize, Ordering::SeqCst};
 use crate::sync::Mutex;
 use crate::sys_common::backtrace::{lock, output_filename};
 use crate::vec::Vec;
-use backtrace::BytesOrWideString;
-use backtrace_rs as backtrace;
 
 /// A captured OS thread stack backtrace.
 ///
@@ -150,7 +149,7 @@ struct BacktraceFrame {
 }
 
 enum RawFrame {
-    Actual(backtrace::Frame),
+    Actual(backtrace_rs::Frame),
     #[cfg(test)]
     Fake,
 }
@@ -197,7 +196,7 @@ impl fmt::Debug for BacktraceSymbol {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(fmt, "{{ ")?;
 
-        if let Some(fn_name) = self.name.as_ref().map(|b| backtrace::SymbolName::new(b)) {
+        if let Some(fn_name) = self.name.as_ref().map(|b| backtrace_rs::SymbolName::new(b)) {
             write!(fmt, "fn: \"{:#}\"", fn_name)?;
         } else {
             write!(fmt, "fn: <unknown>")?;
@@ -223,7 +222,7 @@ impl fmt::Debug for BytesOrWide {
                 BytesOrWide::Bytes(w) => BytesOrWideString::Bytes(w),
                 BytesOrWide::Wide(w) => BytesOrWideString::Wide(w),
             },
-            backtrace::PrintFmt::Short,
+            backtrace_rs::PrintFmt::Short,
             crate::env::current_dir().as_ref().ok(),
         )
     }
@@ -299,7 +298,7 @@ impl Backtrace {
         let mut frames = Vec::new();
         let mut actual_start = None;
         unsafe {
-            backtrace::trace_unsynchronized(|frame| {
+            backtrace_rs::trace_unsynchronized(|frame| {
                 frames.push(BacktraceFrame {
                     frame: RawFrame::Actual(frame.clone()),
                     symbols: Vec::new(),
@@ -350,9 +349,9 @@ impl fmt::Display for Backtrace {
 
         let full = fmt.alternate();
         let (frames, style) = if full {
-            (&capture.frames[..], backtrace::PrintFmt::Full)
+            (&capture.frames[..], backtrace_rs::PrintFmt::Full)
         } else {
-            (&capture.frames[capture.actual_start..], backtrace::PrintFmt::Short)
+            (&capture.frames[capture.actual_start..], backtrace_rs::PrintFmt::Short)
         };
 
         // When printing paths we try to strip the cwd if it exists, otherwise
@@ -364,7 +363,7 @@ impl fmt::Display for Backtrace {
             output_filename(fmt, path, style, cwd.as_ref().ok())
         };
 
-        let mut f = backtrace::BacktraceFmt::new(fmt, style, &mut print_path);
+        let mut f = backtrace_rs::BacktraceFmt::new(fmt, style, &mut print_path);
         f.add_context()?;
         for frame in frames {
             let mut f = f.frame();
@@ -374,7 +373,7 @@ impl fmt::Display for Backtrace {
                 for symbol in frame.symbols.iter() {
                     f.print_raw(
                         frame.frame.ip(),
-                        symbol.name.as_ref().map(|b| backtrace::SymbolName::new(b)),
+                        symbol.name.as_ref().map(|b| backtrace_rs::SymbolName::new(b)),
                         symbol.filename.as_ref().map(|b| match b {
                             BytesOrWide::Bytes(w) => BytesOrWideString::Bytes(w),
                             BytesOrWide::Wide(w) => BytesOrWideString::Wide(w),
@@ -409,7 +408,7 @@ impl Capture {
                 RawFrame::Fake => unimplemented!(),
             };
             unsafe {
-                backtrace::resolve_frame_unsynchronized(frame, |symbol| {
+                backtrace_rs::resolve_frame_unsynchronized(frame, |symbol| {
                     symbols.push(BacktraceSymbol {
                         name: symbol.name().map(|m| m.as_bytes().to_vec()),
                         filename: symbol.filename_raw().map(|b| match b {
diff --git a/src/libstd/build.rs b/src/libstd/build.rs
index eb2753d6245..58fb6fda19a 100644
--- a/src/libstd/build.rs
+++ b/src/libstd/build.rs
@@ -87,4 +87,5 @@ fn main() {
         println!("cargo:rustc-cfg=feature=\"restricted-std\"");
     }
     println!("cargo:rustc-env=STD_ENV_ARCH={}", env::var("CARGO_CFG_TARGET_ARCH").unwrap());
+    println!("cargo:rustc-cfg=backtrace_in_libstd");
 }
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 54fc35b20f7..090dbe3d39e 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -508,6 +508,10 @@ mod panicking;
 // compiler
 pub mod rt;
 
+#[path = "../backtrace/src/lib.rs"]
+#[allow(dead_code, unused_attributes)]
+mod backtrace_rs;
+
 // Pull in the `std_detect` crate directly into libstd. The contents of
 // `std_detect` are in a different repository: rust-lang/stdarch.
 //
diff --git a/src/libstd/panicking.rs b/src/libstd/panicking.rs
index 9542e7209b4..ab2a6010306 100644
--- a/src/libstd/panicking.rs
+++ b/src/libstd/panicking.rs
@@ -171,7 +171,7 @@ fn default_hook(info: &PanicInfo<'_>) {
     // If this is a double panic, make sure that we print a backtrace
     // for this panic. Otherwise only print it if logging is enabled.
     let backtrace_env = if panic_count::get() >= 2 {
-        RustBacktrace::Print(backtrace_rs::PrintFmt::Full)
+        RustBacktrace::Print(crate::backtrace_rs::PrintFmt::Full)
     } else {
         backtrace::rust_backtrace_env()
     };
diff --git a/src/libstd/sys_common/backtrace.rs b/src/libstd/sys_common/backtrace.rs
index e9b1e86d7ae..d386a656e4f 100644
--- a/src/libstd/sys_common/backtrace.rs
+++ b/src/libstd/sys_common/backtrace.rs
@@ -1,3 +1,4 @@
+use crate::backtrace_rs::{self, BacktraceFmt, BytesOrWideString, PrintFmt};
 use crate::borrow::Cow;
 /// Common code for printing the backtrace in the same way across the different
 /// supported platforms.
@@ -9,8 +10,6 @@ use crate::path::{self, Path, PathBuf};
 use crate::sync::atomic::{self, Ordering};
 use crate::sys::mutex::Mutex;
 
-use backtrace_rs::{BacktraceFmt, BytesOrWideString, PrintFmt};
-
 /// Max number of frames to print.
 const MAX_NB_FRAMES: usize = 100;
 
diff --git a/src/tools/tidy/src/deps.rs b/src/tools/tidy/src/deps.rs
index b7d3d428cd2..eeea47b7aa3 100644
--- a/src/tools/tidy/src/deps.rs
+++ b/src/tools/tidy/src/deps.rs
@@ -17,6 +17,7 @@ const LICENSES: &[&str] = &[
     "MIT",
     "Unlicense/MIT",
     "Unlicense OR MIT",
+    "0BSD OR MIT OR Apache-2.0", // adler license
 ];
 
 /// These are exceptions to Rust's permissive licensing policy, and
@@ -36,7 +37,6 @@ const EXCEPTIONS: &[(&str, &str)] = &[
     ("ryu", "Apache-2.0 OR BSL-1.0"),       // rls/cargo/... (because of serde)
     ("bytesize", "Apache-2.0"),             // cargo
     ("im-rc", "MPL-2.0+"),                  // cargo
-    ("adler32", "BSD-3-Clause AND Zlib"),   // cargo dep that isn't used
     ("constant_time_eq", "CC0-1.0"),        // rustfmt
     ("sized-chunks", "MPL-2.0+"),           // cargo via im-rc
     ("bitmaps", "MPL-2.0+"),                // cargo via im-rc
@@ -57,7 +57,8 @@ const RESTRICTED_DEPENDENCY_CRATES: &[&str] = &["rustc_middle", "rustc_codegen_l
 /// This list is here to provide a speed-bump to adding a new dependency to
 /// rustc. Please check with the compiler team before adding an entry.
 const PERMITTED_DEPENDENCIES: &[&str] = &[
-    "adler32",
+    "addr2line",
+    "adler",
     "aho-corasick",
     "annotate-snippets",
     "ansi_term",
@@ -65,7 +66,6 @@ const PERMITTED_DEPENDENCIES: &[&str] = &[
     "atty",
     "autocfg",
     "backtrace",
-    "backtrace-sys",
     "bitflags",
     "block-buffer",
     "block-padding",
@@ -98,6 +98,7 @@ const PERMITTED_DEPENDENCIES: &[&str] = &[
     "generic-array",
     "getopts",
     "getrandom",
+    "gimli",
     "hashbrown",
     "hermit-abi",
     "humantime",
@@ -119,6 +120,7 @@ const PERMITTED_DEPENDENCIES: &[&str] = &[
     "miniz_oxide",
     "nodrop",
     "num_cpus",
+    "object",
     "once_cell",
     "opaque-debug",
     "parking_lot",
diff --git a/src/tools/tidy/src/lib.rs b/src/tools/tidy/src/lib.rs
index b4aafb815fc..c0671596e19 100644
--- a/src/tools/tidy/src/lib.rs
+++ b/src/tools/tidy/src/lib.rs
@@ -60,6 +60,7 @@ fn filter_dirs(path: &Path) -> bool {
         "src/tools/rust-installer",
         "src/tools/rustfmt",
         "src/doc/book",
+        "src/backtrace",
         // Filter RLS output directories
         "target/rls",
     ];