Auto merge of #143613 - Enselic:panic-abort-uwtables, r=petrochenkov

Fix backtraces with `-C panic=abort` on linux; emit unwind tables by default

The linux backtrace unwinder relies on unwind tables to work properly, and generating and printing a backtrace is done by for example the default panic hook.

Begin emitting unwind tables by default again with `-C panic=abort` (see history below) so that backtraces work.

Closes https://github.com/rust-lang/rust/issues/81902 which is **regression-from-stable-to-stable**
Closes https://github.com/rust-lang/rust/issues/94815

### History

Backtraces with `-C panic=abort` used to work in Rust 1.22 but broke in Rust 1.23, because in 1.23 we stopped emitting unwind tables with `-C panic=abort` (see https://github.com/rust-lang/rust/pull/45031 and https://github.com/rust-lang/rust/issues/81902#issuecomment-3046487084).

In 1.45 a workaround in the form of `-C force-unwind-tables=yes` was added (see https://github.com/rust-lang/rust/pull/69984).

`-C panic=abort` was added in [Rust 1.10](https://blog.rust-lang.org/2016/07/07/Rust-1.10/#what-s-in-1-10-stable) and the motivation was binary size and compile time. But given how confusing that behavior has turned out to be, it is better to make binary size optimization opt-in with `-C force-unwind-tables=no` rather than default since the current default breaks backtraces.

Besides, if binary size is a primary concern, there are many other tricks that can be used that has a higher impact.

# Release Note Entry Draft:

## Compatibility Notes

* [Fix backtraces with `-C panic=abort` on Linux by generating unwind tables by default](https://github.com/rust-lang/rust/pull/143613). Build with `-C force-unwind-tables=no` to keep omitting unwind tables.

try-job: aarch64-apple
try-job: armhf-gnu
try-job: aarch64-msvc-1

1 files changed, 7 insertions, 4 deletions

diff --git a/tests/run-make/panic-abort-eh_frame/rmake.rs b/tests/run-make/panic-abort-eh_frame/rmake.rs
index 23d95dc5774..2eccde62795 100644
--- a/tests/run-make/panic-abort-eh_frame/rmake.rs
+++ b/tests/run-make/panic-abort-eh_frame/rmake.rs
@@ -1,9 +1,11 @@
 // An `.eh_frame` section in an object file is a symptom of an UnwindAction::Terminate
 // being inserted, useful for determining whether or not unwinding is necessary.
-// This is useless when panics would NEVER unwind due to -C panic=abort. This section should
-// therefore never appear in the emit file of a -C panic=abort compilation, and this test
-// checks that this is respected.
-// See https://github.com/rust-lang/rust/pull/112403
+// This is useless when panics would NEVER unwind due to -C panic=abort and when we don't need
+// being able to generate backtraces (which depend on unwind tables on linux). This section should
+// therefore never appear in the emit file of a -C panic=abort compilation
+// with -C force-unwind-tables=no, and this test checks that this is respected.
+// See https://github.com/rust-lang/rust/pull/112403 and
+// https://github.com/rust-lang/rust/pull/143613.
 
 //@ only-linux
 // FIXME(Oneirical): the DW_CFA symbol appears on Windows-gnu, because uwtable
@@ -19,6 +21,7 @@ fn main() {
         .panic("abort")
         .edition("2021")
         .arg("-Zvalidate-mir")
+        .arg("-Cforce-unwind-tables=no")
         .run();
     llvm_objdump().arg("--dwarf=frames").input("foo.o").run().assert_stdout_not_contains("DW_CFA");
 }