objtool/rust: add one more `noreturn` Rust function

When the pointer formatting series [1] is applied and KUnit tests are enabled, objtool would report an error with any of our supported Rust versions. For instance, with Rust 1.97.1:

rust/kernel.o: error: objtool: _R..._4core3fmt7Pointer3fmtB7_() falls through to next function _R..._4core7convert5AsRefNtB5_4BStrE6as_ref()

Or, with Rust 1.85.0:

rust/kernel.o: error: objtool: _R..._4core3fmt7Pointer3fmtB7_()
falls through to next function _R..._4core3ffi5c_str4CStrENtNtBS_3fmt7Display3fmtB7_()

This happens due to calls to the noreturn symbol:

core::str::slice_error_fail

Thus add the mangled one to the list so that objtool knows it is actually noreturn.

See commit 56d680dd23c3 ("objtool/rust: list noreturn Rust functions") for more details.

---
 tools/objtool/check.c | 1 +
 1 file changed, 1 insertion(+)

index 87db9f4ed9e2..3ab5b9f1c6a4 100644
@@ -195,6 +195,7 @@ static bool is_rust_noreturn(const struct symbol *func)
 	return str_ends_with(func->name, "_4core3num20from_str_radix_panic")				||
 	       str_ends_with(func->name, "_4core3num22from_ascii_radix_panic")				||
 	       str_ends_with(func->name, "_4core3num28from_ascii_bytes_radix_panic")			||
+	       str_ends_with(func->name, "_4core3str16slice_error_fail")				||
 	       str_ends_with(func->name, "_4core5sliceSp15copy_from_slice17len_mismatch_fail")		||
 	       str_ends_with(func->name, "_4core6option13expect_failed")				||
 	       str_ends_with(func->name, "_4core6option13unwrap_failed")				||

base-commit: dc01dfb37b34beeefcfe1c3055364d41a4070c7e

2.55.0

With the version that I applied of that series, this was not strictly needed anymore.

Cheers,
Miguel

I am seeing this function causing issue on my 1.85.1 -Os build, although the error message is different this time:

rust/kernel.o: warning: objtool: _RNvXs2_NtNtCsaNryh1j6xD7_4core3str6traitseINtNtNtB9_3ops5index5IndexINtNtBJ_5range9RangeFromjEE5indexCsldbe0TGTmNx_6kernel+0x1d: stack state mismatch: cfa1=4+8 cfa2=4+16

Disassembly shows that the function call before the warning location is a call to _4core3str16slice_error_fail, and objtool thought it can return (which will end up with a unbalanced stack if it does return).

Applying the patch fixes the issue.

Best,
Gary

Thanks Gary, then I will pick it up.

Cheers,
Miguel

Applied to rust-fixes -- thanks!

[ While the series [1] mentioned above was not applied in a way
that triggered this, Gary found another case [2]:

I am seeing this function causing issue on my 1.85.1 -Os
build, although the
error message is different this time:

rust/kernel.o: warning: objtool:
_R..._5range9RangeFromjEE5indexCsldbe0TGTmNx_6kernel+0x1d:
stack state mismatch: cfa1=4+8 cfa2=4+16

Disassembly shows that the function call before the warning location is a call to _4core3str16slice_error_fail, and objtool thought it can return (which will end up with a unbalanced stack if it does return).

Thus apply it. - Miguel ]

Cc: [email protected] # Needed in 6.12.y and later (Rust is
pinned in older LTSs).

Cheers,
Miguel