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This patch adds a `-Z linker-flavor` flag to rustc which can be used to invoke
the linker using a different interface.
For example, by default rustc assumes that all the Linux targets will be linked
using GCC. This makes it impossible to use LLD as a linker using just `-C
linker=ld.lld` because that will invoke LLD with invalid command line
arguments. (e.g. rustc will pass -Wl,--gc-sections to LLD but LLD doesn't
understand that; --gc-sections would be the right argument)
With this patch one can pass `-Z linker-flavor=ld` to rustc to invoke the linker
using a LD-like interface. This way, `rustc -C linker=ld.lld -Z
linker-flavor=ld` will invoke LLD with the right arguments.
`-Z linker-flavor` accepts 4 different arguments: `em` (emcc), `ld`,
`gcc`, `msvc` (link.exe). `em`, `gnu` and `msvc` cover all the existing linker
interfaces. `ld` is a new flavor for interfacing GNU's ld and LLD.
This patch also changes target specifications. `linker-flavor` is now a
mandatory field that specifies the *default* linker flavor that the target will
use. This change also makes the linker interface *explicit*; before, it used to
be derived from other fields like linker-is-gnu, is-like-msvc,
is-like-emscripten, etc.
Another change to target specifications is that the fields `pre-link-args`,
`post-link-args` and `late-link-args` now expect a map from flavor to linker
arguments.
``` diff
- "pre-link-args": ["-Wl,--as-needed", "-Wl,-z,-noexecstack"],
+ "pre-link-args": {
+ "gcc": ["-Wl,--as-needed", "-Wl,-z,-noexecstack"],
+ "ld": ["--as-needed", "-z,-noexecstack"],
+ },
```
[breaking-change] for users of custom targets specifications
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#[used] attribute
(For an explanation of what this feature does, read the commit message)
I'd like to propose landing this as an experimental feature (experimental as in:
no clear stabilization path -- like `asm!`, `#[linkage]`) as it's low
maintenance (I think) and relevant to the "Usage in resource-constrained
environments" exploration area.
The main use case I see is running code before `main`. This could be used, for
instance, to cheaply initialize an allocator before `main` where the alternative
is to use `lazy_static` to initialize the allocator on its first use which it's
more expensive (atomics) and doesn't work on ARM Cortex-M0 microcontrollers (no
`AtomicUsize` on that platform)
Here's a `std` example of that:
``` rust
unsafe extern "C" fn before_main_1() {
println!("Hello");
}
unsafe extern "C" fn before_main_2() {
println!("World");
}
#[link_section = ".init_arary"]
#[used]
static INIT_ARRAY: [unsafe extern "C" fn(); 2] = [before_main_1, before_main_2];
fn main() {
println!("Goodbye");
}
```
```
$ rustc -C lto -C opt-level=3 before_main.rs
$ ./before_main
Hello
World
Goodbye
```
In general, this pattern could be used to let *dependencies* run code before
`main` (which sounds like it could go very wrong in some cases). There are
probably other use cases; I hope that the people I have cc-ed can comment on
those.
Note that I'm personally unsure if the above pattern is something we want to
promote / allow and that's why I'm proposing this feature as experimental. If
this leads to more footguns than benefits then we can just axe the feature.
cc @nikomatsakis ^ I know you have some thoughts on having a process for
experimental features though I'm fine with writing an RFC before landing this.
- `dead_code` lint will have to be updated to special case `#[used]` symbols.
- Should we extend `#[used]` to work on non-generic functions?
cc rust-lang/rfcs#1002
cc rust-lang/rfcs#1459
cc @dpc @JinShil
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the nm in our macOS bots don't support that flag and it's not really required
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it's not related to this feature
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Handle extern functions and statics in save-analysis
r? @eddyb
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Properly adjust filenames when multiple emissions
Fixes #40993
Should backport just fine to beta but not sure if we want to do this since this is quite old stable regression.
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rustc: Stabilize the `#![windows_subsystem]` attribute
This commit stabilizes the `#![windows_subsystem]` attribute which is a
conservative exposure of the `/SUBSYSTEM` linker flag on Widnows platforms. This
is useful for creating applications as well as console programs.
Closes #37499
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Fixes #40993
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save-analysis: track associated types
r? @eddyb
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This commit stabilizes the `#![windows_subsystem]` attribute which is a
conservative exposure of the `/SUBSYSTEM` linker flag on Widnows platforms. This
is useful for creating applications as well as console programs.
Closes #37499
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They are so annoying to update, and haven't caught any bugs afaik.
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Rollup of 12 pull requests
- Successful merges: #40146, #40299, #40315, #40319, #40344, #40345, #40372, #40373, #40400, #40404, #40419, #40431
- Failed merges:
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syntax: add `ast::ItemKind::MacroDef`, simplify hygiene info
This PR
- adds a new variant `MacroDef` to `ast::ItemKind` for `macro_rules!` and eventually `macro` items,
- [breaking-change] forbids macro defs without a name (`macro_rules! { () => {} }` compiles today),
- removes `ast::MacroDef`, and
- no longer uses `Mark` and `Invocation` to identify and characterize macro definitions.
- We used to apply (at least) two `Mark`s to an expanded identifier's `SyntaxContext` -- the definition mark(s) and the expansion mark(s). We now only apply the latter.
r? @nrc
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Fix UB in repr(packed) tests
r? @arielb1
cc #37609 and #27060
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This commit alters the compiler to exit quickly if the only output being emitted
is `dep-info`, which doesn't need a lot of other information to generate.
Closes #40328
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Add a reference to the dl library to the Makefile of the test issue-2…
…4445.
It prevents the test to fail on ppc64el at least.
Part of #39015
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Add a test that -fPIC is applied
r? @alexcrichton Can it really be this simple? I've tested it works, but still testing that it used to fail.
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It prevents the test to fail on ppc64el at least.
Part of #39015
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Normalize labeled and unlabeled breaks
Part of #39849.
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As we continue to add more crates to the compiler and use them to implement
various features we want to be sure we're not accidentally expanding the API
surface area of the compiler! To that end this commit adds a new `run-make` test
which will attempt to `extern crate foo` all crates in the sysroot, verifying
that they're all unstable.
This commit discovered that the `std_shim` and `test_shim` crates were
accidentally stable and fixes the situation by deleting those shims. The shims
are no longer necessary due to changes in Cargo that have happened since they
were originally incepted.
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test: Remove sanitizer-thread test
Unfortunately it appears to spuriously fail so we can't gate on it
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Unfortunately it appears to spuriously fail so we can't gate on it
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This reverts commit 9903975003276cc42a1ed5f21eee292b7c62c331.
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Add 128-bit atomics
This is currently only supported on AArch64 since that is the only target which unconditionally supports 128-bit atomic operations.
cc #35118
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Implement kind="static-nobundle" (RFC 1717)
This implements the "static-nobundle" library kind (last item from #37403).
Rustc handles "static-nobundle" libs very similarly to dylibs, except that on Windows, uses of their symbols do not get marked with "dllimport". Which is the whole point of this feature.
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These are static libraries that are not bundled (as the name implies) into rlibs and staticlibs that rustc generates,
and must be present when the final binary artifact is being linked.
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during CGU partitioning.
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