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, 367 insertions, 0 deletions

diff --git a/arch/arm/nwfpe/softfloat-specialize b/arch/arm/nwfpe/softfloat-specialize
new file mode 100644
index 000000000..679a0269d
--- /dev/null
+++ b/arch/arm/nwfpe/softfloat-specialize
@@ -0,0 +1,367 @@
+
+/*
+===============================================================================
+
+This C source fragment is part of the SoftFloat IEC/IEEE Floating-point
+Arithmetic Package, Release 2.
+
+Written by John R. Hauser.  This work was made possible in part by the
+International Computer Science Institute, located at Suite 600, 1947 Center
+Street, Berkeley, California 94704.  Funding was partially provided by the
+National Science Foundation under grant MIP-9311980.  The original version
+of this code was written as part of a project to build a fixed-point vector
+processor in collaboration with the University of California at Berkeley,
+overseen by Profs. Nelson Morgan and John Wawrzynek.  More information
+is available through the Web page
+http://www.jhauser.us/arithmetic/SoftFloat-2b/SoftFloat-source.txt
+
+THIS SOFTWARE IS DISTRIBUTED AS IS, FOR FREE.  Although reasonable effort
+has been made to avoid it, THIS SOFTWARE MAY CONTAIN FAULTS THAT WILL AT
+TIMES RESULT IN INCORRECT BEHAVIOR.  USE OF THIS SOFTWARE IS RESTRICTED TO
+PERSONS AND ORGANIZATIONS WHO CAN AND WILL TAKE FULL RESPONSIBILITY FOR ANY
+AND ALL LOSSES, COSTS, OR OTHER PROBLEMS ARISING FROM ITS USE.
+
+Derivative works are acceptable, even for commercial purposes, so long as
+(1) they include prominent notice that the work is derivative, and (2) they
+include prominent notice akin to these three paragraphs for those parts of
+this code that are retained.
+
+===============================================================================
+*/
+
+/*
+-------------------------------------------------------------------------------
+Underflow tininess-detection mode, statically initialized to default value.
+(The declaration in `softfloat.h' must match the `int8' type here.)
+-------------------------------------------------------------------------------
+*/
+int8 float_detect_tininess = float_tininess_after_rounding;
+
+/*
+-------------------------------------------------------------------------------
+Raises the exceptions specified by `flags'.  Floating-point traps can be
+defined here if desired.  It is currently not possible for such a trap to
+substitute a result value.  If traps are not implemented, this routine
+should be simply `float_exception_flags |= flags;'.
+
+ScottB:  November 4, 1998
+Moved this function out of softfloat-specialize into fpmodule.c.
+This effectively isolates all the changes required for integrating with the
+Linux kernel into fpmodule.c.  Porting to NetBSD should only require modifying
+fpmodule.c to integrate with the NetBSD kernel (I hope!).
+-------------------------------------------------------------------------------
+void float_raise( int8 flags )
+{
+    float_exception_flags |= flags;
+}
+*/
+
+/*
+-------------------------------------------------------------------------------
+Internal canonical NaN format.
+-------------------------------------------------------------------------------
+*/
+typedef struct {
+    flag sign;
+    bits64 high, low;
+} commonNaNT;
+
+/*
+-------------------------------------------------------------------------------
+The pattern for a default generated single-precision NaN.
+-------------------------------------------------------------------------------
+*/
+#define float32_default_nan 0xFFFFFFFF
+
+/*
+-------------------------------------------------------------------------------
+Returns 1 if the single-precision floating-point value `a' is a NaN;
+otherwise returns 0.
+-------------------------------------------------------------------------------
+*/
+flag float32_is_nan( float32 a )
+{
+
+    return ( 0xFF000000 < (bits32) ( a<<1 ) );
+
+}
+
+/*
+-------------------------------------------------------------------------------
+Returns 1 if the single-precision floating-point value `a' is a signaling
+NaN; otherwise returns 0.
+-------------------------------------------------------------------------------
+*/
+flag float32_is_signaling_nan( float32 a )
+{
+
+    return ( ( ( a>>22 ) & 0x1FF ) == 0x1FE ) && ( a & 0x003FFFFF );
+
+}
+
+/*
+-------------------------------------------------------------------------------
+Returns the result of converting the single-precision floating-point NaN
+`a' to the canonical NaN format.  If `a' is a signaling NaN, the invalid
+exception is raised.
+-------------------------------------------------------------------------------
+*/
+static commonNaNT float32ToCommonNaN( float32 a )
+{
+    commonNaNT z;
+
+    if ( float32_is_signaling_nan( a ) ) float_raise( float_flag_invalid );
+    z.sign = a>>31;
+    z.low = 0;
+    z.high = ( (bits64) a )<<41;
+    return z;
+
+}
+
+/*
+-------------------------------------------------------------------------------
+Returns the result of converting the canonical NaN `a' to the single-
+precision floating-point format.
+-------------------------------------------------------------------------------
+*/
+static float32 commonNaNToFloat32( commonNaNT a )
+{
+
+    return ( ( (bits32) a.sign )<<31 ) | 0x7FC00000 | ( a.high>>41 );
+
+}
+
+/*
+-------------------------------------------------------------------------------
+Takes two single-precision floating-point values `a' and `b', one of which
+is a NaN, and returns the appropriate NaN result.  If either `a' or `b' is a
+signaling NaN, the invalid exception is raised.
+-------------------------------------------------------------------------------
+*/
+static float32 propagateFloat32NaN( float32 a, float32 b )
+{
+    flag aIsNaN, aIsSignalingNaN, bIsNaN, bIsSignalingNaN;
+
+    aIsNaN = float32_is_nan( a );
+    aIsSignalingNaN = float32_is_signaling_nan( a );
+    bIsNaN = float32_is_nan( b );
+    bIsSignalingNaN = float32_is_signaling_nan( b );
+    a |= 0x00400000;
+    b |= 0x00400000;
+    if ( aIsSignalingNaN | bIsSignalingNaN ) float_raise( float_flag_invalid );
+    if ( aIsNaN ) {
+        return ( aIsSignalingNaN & bIsNaN ) ? b : a;
+    }
+    else {
+        return b;
+    }
+
+}
+
+/*
+-------------------------------------------------------------------------------
+The pattern for a default generated double-precision NaN.
+-------------------------------------------------------------------------------
+*/
+#define float64_default_nan LIT64( 0xFFFFFFFFFFFFFFFF )
+
+/*
+-------------------------------------------------------------------------------
+Returns 1 if the double-precision floating-point value `a' is a NaN;
+otherwise returns 0.
+-------------------------------------------------------------------------------
+*/
+flag float64_is_nan( float64 a )
+{
+
+    return ( LIT64( 0xFFE0000000000000 ) < (bits64) ( a<<1 ) );
+
+}
+
+/*
+-------------------------------------------------------------------------------
+Returns 1 if the double-precision floating-point value `a' is a signaling
+NaN; otherwise returns 0.
+-------------------------------------------------------------------------------
+*/
+flag float64_is_signaling_nan( float64 a )
+{
+
+    return
+           ( ( ( a>>51 ) & 0xFFF ) == 0xFFE )
+        && ( a & LIT64( 0x0007FFFFFFFFFFFF ) );
+
+}
+
+/*
+-------------------------------------------------------------------------------
+Returns the result of converting the double-precision floating-point NaN
+`a' to the canonical NaN format.  If `a' is a signaling NaN, the invalid
+exception is raised.
+-------------------------------------------------------------------------------
+*/
+static commonNaNT float64ToCommonNaN( float64 a )
+{
+    commonNaNT z;
+
+    if ( float64_is_signaling_nan( a ) ) float_raise( float_flag_invalid );
+    z.sign = a>>63;
+    z.low = 0;
+    z.high = a<<12;
+    return z;
+
+}
+
+/*
+-------------------------------------------------------------------------------
+Returns the result of converting the canonical NaN `a' to the double-
+precision floating-point format.
+-------------------------------------------------------------------------------
+*/
+static float64 commonNaNToFloat64( commonNaNT a )
+{
+
+    return
+          ( ( (bits64) a.sign )<<63 )
+        | LIT64( 0x7FF8000000000000 )
+        | ( a.high>>12 );
+
+}
+
+/*
+-------------------------------------------------------------------------------
+Takes two double-precision floating-point values `a' and `b', one of which
+is a NaN, and returns the appropriate NaN result.  If either `a' or `b' is a
+signaling NaN, the invalid exception is raised.
+-------------------------------------------------------------------------------
+*/
+static float64 propagateFloat64NaN( float64 a, float64 b )
+{
+    flag aIsNaN, aIsSignalingNaN, bIsNaN, bIsSignalingNaN;
+
+    aIsNaN = float64_is_nan( a );
+    aIsSignalingNaN = float64_is_signaling_nan( a );
+    bIsNaN = float64_is_nan( b );
+    bIsSignalingNaN = float64_is_signaling_nan( b );
+    a |= LIT64( 0x0008000000000000 );
+    b |= LIT64( 0x0008000000000000 );
+    if ( aIsSignalingNaN | bIsSignalingNaN ) float_raise( float_flag_invalid );
+    if ( aIsNaN ) {
+        return ( aIsSignalingNaN & bIsNaN ) ? b : a;
+    }
+    else {
+        return b;
+    }
+
+}
+
+#ifdef FLOATX80
+
+/*
+-------------------------------------------------------------------------------
+The pattern for a default generated extended double-precision NaN.  The
+`high' and `low' values hold the most- and least-significant bits,
+respectively.
+-------------------------------------------------------------------------------
+*/
+#define floatx80_default_nan_high 0xFFFF
+#define floatx80_default_nan_low  LIT64( 0xFFFFFFFFFFFFFFFF )
+
+/*
+-------------------------------------------------------------------------------
+Returns 1 if the extended double-precision floating-point value `a' is a
+NaN; otherwise returns 0.
+-------------------------------------------------------------------------------
+*/
+flag floatx80_is_nan( floatx80 a )
+{
+
+    return ( ( a.high & 0x7FFF ) == 0x7FFF ) && (bits64) ( a.low<<1 );
+
+}
+
+/*
+-------------------------------------------------------------------------------
+Returns 1 if the extended double-precision floating-point value `a' is a
+signaling NaN; otherwise returns 0.
+-------------------------------------------------------------------------------
+*/
+flag floatx80_is_signaling_nan( floatx80 a )
+{
+    //register int lr;
+    bits64 aLow;
+
+    //__asm__("mov %0, lr" : : "g" (lr));
+    //fp_printk("floatx80_is_signalling_nan() called from 0x%08x\n",lr);
+    aLow = a.low & ~ LIT64( 0x4000000000000000 );
+    return
+           ( ( a.high & 0x7FFF ) == 0x7FFF )
+        && (bits64) ( aLow<<1 )
+        && ( a.low == aLow );
+
+}
+
+/*
+-------------------------------------------------------------------------------
+Returns the result of converting the extended double-precision floating-
+point NaN `a' to the canonical NaN format.  If `a' is a signaling NaN, the
+invalid exception is raised.
+-------------------------------------------------------------------------------
+*/
+static commonNaNT floatx80ToCommonNaN( floatx80 a )
+{
+    commonNaNT z;
+
+    if ( floatx80_is_signaling_nan( a ) ) float_raise( float_flag_invalid );
+    z.sign = a.high>>15;
+    z.low = 0;
+    z.high = a.low<<1;
+    return z;
+
+}
+
+/*
+-------------------------------------------------------------------------------
+Returns the result of converting the canonical NaN `a' to the extended
+double-precision floating-point format.
+-------------------------------------------------------------------------------
+*/
+static floatx80 commonNaNToFloatx80( commonNaNT a )
+{
+    floatx80 z;
+
+    z.low = LIT64( 0xC000000000000000 ) | ( a.high>>1 );
+    z.high = ( ( (bits16) a.sign )<<15 ) | 0x7FFF;
+    z.__padding = 0;
+    return z;
+
+}
+
+/*
+-------------------------------------------------------------------------------
+Takes two extended double-precision floating-point values `a' and `b', one
+of which is a NaN, and returns the appropriate NaN result.  If either `a' or
+`b' is a signaling NaN, the invalid exception is raised.
+-------------------------------------------------------------------------------
+*/
+static floatx80 propagateFloatx80NaN( floatx80 a, floatx80 b )
+{
+    flag aIsNaN, aIsSignalingNaN, bIsNaN, bIsSignalingNaN;
+
+    aIsNaN = floatx80_is_nan( a );
+    aIsSignalingNaN = floatx80_is_signaling_nan( a );
+    bIsNaN = floatx80_is_nan( b );
+    bIsSignalingNaN = floatx80_is_signaling_nan( b );
+    a.low |= LIT64( 0xC000000000000000 );
+    b.low |= LIT64( 0xC000000000000000 );
+    if ( aIsSignalingNaN | bIsSignalingNaN ) float_raise( float_flag_invalid );
+    if ( aIsNaN ) {
+        return ( aIsSignalingNaN & bIsNaN ) ? b : a;
+    }
+    else {
+        return b;
+    }
+
+}
+
+#endif