kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 208 insertions, 0 deletions

diff --git a/include/math-emu/quad.h b/include/math-emu/quad.h
new file mode 100644
index 000000000..616113626
--- /dev/null
+++ b/include/math-emu/quad.h
@@ -0,0 +1,208 @@
+/* Software floating-point emulation.
+   Definitions for IEEE Quad Precision.
+   Copyright (C) 1997,1998,1999 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Richard Henderson (rth@cygnus.com),
+		  Jakub Jelinek (jj@ultra.linux.cz),
+		  David S. Miller (davem@redhat.com) and
+		  Peter Maydell (pmaydell@chiark.greenend.org.uk).
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Library General Public License as
+   published by the Free Software Foundation; either version 2 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Library General Public License for more details.
+
+   You should have received a copy of the GNU Library General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If
+   not, write to the Free Software Foundation, Inc.,
+   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
+
+#ifndef  __MATH_EMU_QUAD_H__
+#define  __MATH_EMU_QUAD_H__
+
+#if _FP_W_TYPE_SIZE < 32
+#error "Here's a nickel, kid. Go buy yourself a real computer."
+#endif
+
+#if _FP_W_TYPE_SIZE < 64
+#define _FP_FRACTBITS_Q         (4*_FP_W_TYPE_SIZE)
+#else
+#define _FP_FRACTBITS_Q		(2*_FP_W_TYPE_SIZE)
+#endif
+
+#define _FP_FRACBITS_Q		113
+#define _FP_FRACXBITS_Q		(_FP_FRACTBITS_Q - _FP_FRACBITS_Q)
+#define _FP_WFRACBITS_Q		(_FP_WORKBITS + _FP_FRACBITS_Q)
+#define _FP_WFRACXBITS_Q	(_FP_FRACTBITS_Q - _FP_WFRACBITS_Q)
+#define _FP_EXPBITS_Q		15
+#define _FP_EXPBIAS_Q		16383
+#define _FP_EXPMAX_Q		32767
+
+#define _FP_QNANBIT_Q		\
+	((_FP_W_TYPE)1 << (_FP_FRACBITS_Q-2) % _FP_W_TYPE_SIZE)
+#define _FP_IMPLBIT_Q		\
+	((_FP_W_TYPE)1 << (_FP_FRACBITS_Q-1) % _FP_W_TYPE_SIZE)
+#define _FP_OVERFLOW_Q		\
+	((_FP_W_TYPE)1 << (_FP_WFRACBITS_Q % _FP_W_TYPE_SIZE))
+
+#if _FP_W_TYPE_SIZE < 64
+
+union _FP_UNION_Q
+{
+   long double flt;
+   struct 
+   {
+#if __BYTE_ORDER == __BIG_ENDIAN
+      unsigned sign : 1;
+      unsigned exp : _FP_EXPBITS_Q;
+      unsigned long frac3 : _FP_FRACBITS_Q - (_FP_IMPLBIT_Q != 0)-(_FP_W_TYPE_SIZE * 3);
+      unsigned long frac2 : _FP_W_TYPE_SIZE;
+      unsigned long frac1 : _FP_W_TYPE_SIZE;
+      unsigned long frac0 : _FP_W_TYPE_SIZE;
+#else
+      unsigned long frac0 : _FP_W_TYPE_SIZE;
+      unsigned long frac1 : _FP_W_TYPE_SIZE;
+      unsigned long frac2 : _FP_W_TYPE_SIZE;
+      unsigned long frac3 : _FP_FRACBITS_Q - (_FP_IMPLBIT_Q != 0)-(_FP_W_TYPE_SIZE * 3);
+      unsigned exp : _FP_EXPBITS_Q;
+      unsigned sign : 1;
+#endif /* not bigendian */
+   } bits __attribute__((packed));
+};
+
+
+#define FP_DECL_Q(X)		_FP_DECL(4,X)
+#define FP_UNPACK_RAW_Q(X,val)	_FP_UNPACK_RAW_4(Q,X,val)
+#define FP_UNPACK_RAW_QP(X,val)	_FP_UNPACK_RAW_4_P(Q,X,val)
+#define FP_PACK_RAW_Q(val,X)	_FP_PACK_RAW_4(Q,val,X)
+#define FP_PACK_RAW_QP(val,X)		\
+  do {					\
+    if (!FP_INHIBIT_RESULTS)		\
+      _FP_PACK_RAW_4_P(Q,val,X);	\
+  } while (0)
+
+#define FP_UNPACK_Q(X,val)		\
+  do {					\
+    _FP_UNPACK_RAW_4(Q,X,val);		\
+    _FP_UNPACK_CANONICAL(Q,4,X);	\
+  } while (0)
+
+#define FP_UNPACK_QP(X,val)		\
+  do {					\
+    _FP_UNPACK_RAW_4_P(Q,X,val);	\
+    _FP_UNPACK_CANONICAL(Q,4,X);	\
+  } while (0)
+
+#define FP_PACK_Q(val,X)		\
+  do {					\
+    _FP_PACK_CANONICAL(Q,4,X);		\
+    _FP_PACK_RAW_4(Q,val,X);		\
+  } while (0)
+
+#define FP_PACK_QP(val,X)		\
+  do {					\
+    _FP_PACK_CANONICAL(Q,4,X);		\
+    if (!FP_INHIBIT_RESULTS)		\
+      _FP_PACK_RAW_4_P(Q,val,X);	\
+  } while (0)
+
+#define FP_ISSIGNAN_Q(X)		_FP_ISSIGNAN(Q,4,X)
+#define FP_NEG_Q(R,X)			_FP_NEG(Q,4,R,X)
+#define FP_ADD_Q(R,X,Y)			_FP_ADD(Q,4,R,X,Y)
+#define FP_SUB_Q(R,X,Y)			_FP_SUB(Q,4,R,X,Y)
+#define FP_MUL_Q(R,X,Y)			_FP_MUL(Q,4,R,X,Y)
+#define FP_DIV_Q(R,X,Y)			_FP_DIV(Q,4,R,X,Y)
+#define FP_SQRT_Q(R,X)			_FP_SQRT(Q,4,R,X)
+#define _FP_SQRT_MEAT_Q(R,S,T,X,Q)	_FP_SQRT_MEAT_4(R,S,T,X,Q)
+
+#define FP_CMP_Q(r,X,Y,un)	_FP_CMP(Q,4,r,X,Y,un)
+#define FP_CMP_EQ_Q(r,X,Y)	_FP_CMP_EQ(Q,4,r,X,Y)
+
+#define FP_TO_INT_Q(r,X,rsz,rsg)	_FP_TO_INT(Q,4,r,X,rsz,rsg)
+#define FP_TO_INT_ROUND_Q(r,X,rsz,rsg)	_FP_TO_INT_ROUND(Q,4,r,X,rsz,rsg)
+#define FP_FROM_INT_Q(X,r,rs,rt)	_FP_FROM_INT(Q,4,X,r,rs,rt)
+
+#define _FP_FRAC_HIGH_Q(X)	_FP_FRAC_HIGH_4(X)
+#define _FP_FRAC_HIGH_RAW_Q(X)	_FP_FRAC_HIGH_4(X)
+
+#else   /* not _FP_W_TYPE_SIZE < 64 */
+union _FP_UNION_Q
+{
+  long double flt /* __attribute__((mode(TF))) */ ;
+  struct {
+#if __BYTE_ORDER == __BIG_ENDIAN
+    unsigned sign  : 1;
+    unsigned exp   : _FP_EXPBITS_Q;
+    unsigned long frac1 : _FP_FRACBITS_Q-(_FP_IMPLBIT_Q != 0)-_FP_W_TYPE_SIZE;
+    unsigned long frac0 : _FP_W_TYPE_SIZE;
+#else
+    unsigned long frac0 : _FP_W_TYPE_SIZE;
+    unsigned long frac1 : _FP_FRACBITS_Q-(_FP_IMPLBIT_Q != 0)-_FP_W_TYPE_SIZE;
+    unsigned exp   : _FP_EXPBITS_Q;
+    unsigned sign  : 1;
+#endif
+  } bits;
+};
+
+#define FP_DECL_Q(X)		_FP_DECL(2,X)
+#define FP_UNPACK_RAW_Q(X,val)	_FP_UNPACK_RAW_2(Q,X,val)
+#define FP_UNPACK_RAW_QP(X,val)	_FP_UNPACK_RAW_2_P(Q,X,val)
+#define FP_PACK_RAW_Q(val,X)	_FP_PACK_RAW_2(Q,val,X)
+#define FP_PACK_RAW_QP(val,X)		\
+  do {					\
+    if (!FP_INHIBIT_RESULTS)		\
+      _FP_PACK_RAW_2_P(Q,val,X);	\
+  } while (0)
+
+#define FP_UNPACK_Q(X,val)		\
+  do {					\
+    _FP_UNPACK_RAW_2(Q,X,val);		\
+    _FP_UNPACK_CANONICAL(Q,2,X);	\
+  } while (0)
+
+#define FP_UNPACK_QP(X,val)		\
+  do {					\
+    _FP_UNPACK_RAW_2_P(Q,X,val);	\
+    _FP_UNPACK_CANONICAL(Q,2,X);	\
+  } while (0)
+
+#define FP_PACK_Q(val,X)		\
+  do {					\
+    _FP_PACK_CANONICAL(Q,2,X);		\
+    _FP_PACK_RAW_2(Q,val,X);		\
+  } while (0)
+
+#define FP_PACK_QP(val,X)		\
+  do {					\
+    _FP_PACK_CANONICAL(Q,2,X);		\
+    if (!FP_INHIBIT_RESULTS)		\
+      _FP_PACK_RAW_2_P(Q,val,X);	\
+  } while (0)
+
+#define FP_ISSIGNAN_Q(X)		_FP_ISSIGNAN(Q,2,X)
+#define FP_NEG_Q(R,X)			_FP_NEG(Q,2,R,X)
+#define FP_ADD_Q(R,X,Y)			_FP_ADD(Q,2,R,X,Y)
+#define FP_SUB_Q(R,X,Y)			_FP_SUB(Q,2,R,X,Y)
+#define FP_MUL_Q(R,X,Y)			_FP_MUL(Q,2,R,X,Y)
+#define FP_DIV_Q(R,X,Y)			_FP_DIV(Q,2,R,X,Y)
+#define FP_SQRT_Q(R,X)			_FP_SQRT(Q,2,R,X)
+#define _FP_SQRT_MEAT_Q(R,S,T,X,Q)	_FP_SQRT_MEAT_2(R,S,T,X,Q)
+
+#define FP_CMP_Q(r,X,Y,un)	_FP_CMP(Q,2,r,X,Y,un)
+#define FP_CMP_EQ_Q(r,X,Y)	_FP_CMP_EQ(Q,2,r,X,Y)
+
+#define FP_TO_INT_Q(r,X,rsz,rsg)	_FP_TO_INT(Q,2,r,X,rsz,rsg)
+#define FP_TO_INT_ROUND_Q(r,X,rsz,rsg)	_FP_TO_INT_ROUND(Q,2,r,X,rsz,rsg)
+#define FP_FROM_INT_Q(X,r,rs,rt)	_FP_FROM_INT(Q,2,X,r,rs,rt)
+
+#define _FP_FRAC_HIGH_Q(X)	_FP_FRAC_HIGH_2(X)
+#define _FP_FRAC_HIGH_RAW_Q(X)	_FP_FRAC_HIGH_2(X)
+
+#endif /* not _FP_W_TYPE_SIZE < 64 */
+
+#endif /* __MATH_EMU_QUAD_H__ */