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Auto merge of #125417 - lqd:lld-retry, r=<try>
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self-contained linker: retry linking without `-fuse-ld=lld` on CCs that don't support it

For the self-contained linker, this PR applies [the strategy](#125330 (comment)) of retrying the linking step when the driver doesn't support `-fuse-ld=lld`, but with the option removed. This is the same strategy we already use of retrying when e.g. `-no-pie` is not supported.

Fixes #125330
r? `@petrochenkov`

I have no idea how we could add a test here, much like we don't have one for `-no-pie` or `-static-pie` -- let me know if you have ideas -- but I tested on a CentOS7 image:

```console
[root@d25b38376ede tmp]# ../build/host/stage1/bin/rustc helloworld.rs
 WARN rustc_codegen_ssa::back::link The linker driver does not support `-fuse-ld=lld`. Retrying without it.

[root@d25b38376ede tmp]# readelf -p .comment helloworld

String dump of section '.comment':
  [     0]  GCC: (GNU) 4.8.5 20150623 (Red Hat 4.8.5-44)
  [    2d]  rustc version 1.80.0-dev
```

(I wasn't able to test with `cross` as the issue describes: I wasn't able to reproduce that behavior locally. So I'll ask for help from the OP with a try build)
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bors committed May 22, 2024
2 parents 5d328a1 + 5da41f5 commit 5572f38
Showing 1 changed file with 21 additions and 0 deletions.
21 changes: 21 additions & 0 deletions compiler/rustc_codegen_ssa/src/back/link.rs
Original file line number Diff line number Diff line change
Expand Up @@ -799,6 +799,27 @@ fn link_natively(
continue;
}

// Check if linking failed with an error message that indicates the driver didn't recognize
// the `-fuse-ld=lld` option. If so, re-perform the link step without it. This avoids having
// to spawn multiple instances on the happy path to do version checking, and ensures things
// keep working on the tier 1 baseline of GLIBC 2.17+. That is generally understood as GCCs
// circa RHEL/CentOS 7, 4.5 or so, whereas lld support was added in GCC 9.
if matches!(flavor, LinkerFlavor::Gnu(Cc::Yes, Lld::Yes))
&& unknown_arg_regex.is_match(&out)
&& out.contains("-fuse-ld=lld")
&& cmd.get_args().iter().any(|e| e.to_string_lossy() == "-fuse-ld=lld")
{
info!("linker output: {:?}", out);
warn!("The linker driver does not support `-fuse-ld=lld`. Retrying without it.");
for arg in cmd.take_args() {
if arg.to_string_lossy() != "-fuse-ld=lld" {
cmd.arg(arg);
}
}
info!("{:?}", &cmd);
continue;
}

// Detect '-static-pie' used with an older version of gcc or clang not supporting it.
// Fallback from '-static-pie' to '-static' in that case.
if matches!(flavor, LinkerFlavor::Gnu(Cc::Yes, _))
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