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rustc: Stabilize -Zrun-dsymutil as -Csplit-debuginfo

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This commit adds a new stable codegen option to rustc,
`-Csplit-debuginfo`. The old `-Zrun-dsymutil` flag is deleted and now
subsumed by this stable flag. Additionally `-Zsplit-dwarf` is also
subsumed by this flag but still requires `-Zunstable-options` to
actually activate. The `-Csplit-debuginfo` flag takes one of
three values:

* `off` - This indicates that split-debuginfo from the final artifact is
  not desired. This is not supported on Windows and is the default on
  Unix platforms except macOS. On macOS this means that `dsymutil` is
  not executed.

* `packed` - This means that debuginfo is desired in one location
  separate from the main executable. This is the default on Windows
  (`*.pdb`) and macOS (`*.dSYM`). On other Unix platforms this subsumes
  `-Zsplit-dwarf=single` and produces a `*.dwp` file.

* `unpacked` - This means that debuginfo will be roughly equivalent to
  object files, meaning that it's throughout the build directory
  rather than in one location (often the fastest for local development).
  This is not the default on any platform and is not supported on Windows.

Each target can indicate its own default preference for how debuginfo is
handled. Almost all platforms default to `off` except for Windows and
macOS which default to `packed` for historical reasons.

Some equivalencies for previous unstable flags with the new flags are:

* `-Zrun-dsymutil=yes` -> `-Csplit-debuginfo=packed`
* `-Zrun-dsymutil=no` -> `-Csplit-debuginfo=unpacked`
* `-Zsplit-dwarf=single` -> `-Csplit-debuginfo=packed`
* `-Zsplit-dwarf=split` -> `-Csplit-debuginfo=unpacked`

Note that `-Csplit-debuginfo` still requires `-Zunstable-options` for
non-macOS platforms since split-dwarf support was *just* implemented in
rustc.

There's some more rationale listed on #79361, but the main gist of the
motivation for this commit is that `dsymutil` can take quite a long time
to execute in debug builds and provides little benefit. This means that
incremental compile times appear that much worse on macOS because the
compiler is constantly running `dsymutil` over every single binary it
produces during `cargo build` (even build scripts!). Ideally rustc would
switch to not running `dsymutil` by default, but that's a problem left
to get tackled another day.

Closes #79361
This commit is contained in:
Alex Crichton 2020-11-30 08:39:08 -08:00
parent 7fba12bb1d
commit a124043fb0
21 changed files with 352 additions and 134 deletions
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84
compiler/rustc_codegen_ssa/src/back/link.rs
View file

@ -14,7 +14,7 @@ use rustc_session::utils::NativeLibKind;
use rustc_session::{filesearch, Session};
use rustc_span::symbol::Symbol;
use rustc_target::spec::crt_objects::{CrtObjects, CrtObjectsFallback};
use rustc_target::spec::{LinkOutputKind, LinkerFlavor, LldFlavor};
use rustc_target::spec::{LinkOutputKind, LinkerFlavor, LldFlavor, SplitDebuginfo};
use rustc_target::spec::{PanicStrategy, RelocModel, RelroLevel, Target};
use super::archive::ArchiveBuilder;
@ -99,9 +99,6 @@ pub fn link_binary<'a, B: ArchiveBuilder<'a>>(
path.as_ref(),
target_cpu,
);
if sess.opts.debugging_opts.split_dwarf == config::SplitDwarfKind::Split {
link_dwarf_object(sess, &out_filename);
}
}
}
if sess.opts.json_artifact_notifications {
@ -828,29 +825,43 @@ fn link_natively<'a, B: ArchiveBuilder<'a>>(
}
}
// On macOS, debuggers need this utility to get run to do some munging of
// the symbols. Note, though, that if the object files are being preserved
// for their debug information there's no need for us to run dsymutil.
if sess.target.is_like_osx
&& sess.opts.debuginfo != DebugInfo::None
&& !preserve_objects_for_their_debuginfo(sess)
{
let prog = Command::new("dsymutil").arg(out_filename).output();
match prog {
Ok(prog) => {
if !prog.status.success() {
let mut output = prog.stderr.clone();
output.extend_from_slice(&prog.stdout);
sess.struct_warn(&format!(
"processing debug info with `dsymutil` failed: {}",
prog.status
))
.note(&escape_string(&output))
.emit();
match sess.split_debuginfo() {
// If split debug information is disabled or located in individual files
// there's nothing to do here.
SplitDebuginfo::Off | SplitDebuginfo::Unpacked => {}
// If packed split-debuginfo is requested, but the final compilation
// doesn't actually have any debug information, then we skip this step.
SplitDebuginfo::Packed if sess.opts.debuginfo == DebugInfo::None => {}
// On macOS the external `dsymutil` tool is used to create the packed
// debug information. Note that this will read debug information from
// the objects on the filesystem which we'll clean up later.
SplitDebuginfo::Packed if sess.target.is_like_osx => {
let prog = Command::new("dsymutil").arg(out_filename).output();
match prog {
Ok(prog) => {
if !prog.status.success() {
let mut output = prog.stderr.clone();
output.extend_from_slice(&prog.stdout);
sess.struct_warn(&format!(
"processing debug info with `dsymutil` failed: {}",
prog.status
))
.note(&escape_string(&output))
.emit();
}
}
Err(e) => sess.fatal(&format!("unable to run `dsymutil`: {}", e)),
}
Err(e) => sess.fatal(&format!("unable to run `dsymutil`: {}", e)),
}
// On MSVC packed debug information is produced by the linker itself so
// there's no need to do anything else here.
SplitDebuginfo::Packed if sess.target.is_like_msvc => {}
// ... and otherwise we're processing a `*.dwp` packed dwarf file.
SplitDebuginfo::Packed => link_dwarf_object(sess, &out_filename),
}
}
@ -1050,28 +1061,9 @@ fn preserve_objects_for_their_debuginfo(sess: &Session) -> bool {
return false;
}
// Single mode keeps debuginfo in the same object file, but in such a way that it it skipped
// by the linker - so it's expected that when codegen units are linked together that this
// debuginfo would be lost without keeping around the temps.
if sess.opts.debugging_opts.split_dwarf == config::SplitDwarfKind::Single {
return true;
}
// If we're on OSX then the equivalent of split dwarf is turned on by
// default. The final executable won't actually have any debug information
// except it'll have pointers to elsewhere. Historically we've always run
// `dsymutil` to "link all the dwarf together" but this is actually sort of
// a bummer for incremental compilation! (the whole point of split dwarf is
// that you don't do this sort of dwarf link).
//
// Basically as a result this just means that if we're on OSX and we're
// *not* running dsymutil then the object files are the only source of truth
// for debug information, so we must preserve them.
if sess.target.is_like_osx {
return !sess.opts.debugging_opts.run_dsymutil;
}
false
// "unpacked" split debuginfo means that we leave object files as the
// debuginfo is found in the original object files themselves
sess.split_debuginfo() == SplitDebuginfo::Unpacked
}
pub fn archive_search_paths(sess: &Session) -> Vec<PathBuf> {