From 5febf432df1cfa5b25d99b54c32103fafbdd0eb9 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Sun, 16 Aug 2026 15:32:33 +0200 Subject: kbuild: rust: keep Rust objects out of Clang LTO with inline helpers 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 Cc: Boqun Feng Cc: Alice Ryhl Cc: Matthew Maurer Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: stable@vger.kernel.org Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust") Acked-by: Gary Guo Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org Signed-off-by: Miguel Ojeda --- arch/alpha/lib/divide.S | 199 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 199 insertions(+) create mode 100644 arch/alpha/lib/divide.S (limited to 'arch/alpha/lib/divide.S') diff --git a/arch/alpha/lib/divide.S b/arch/alpha/lib/divide.S new file mode 100644 index 000000000..db01840d7 --- /dev/null +++ b/arch/alpha/lib/divide.S @@ -0,0 +1,199 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * arch/alpha/lib/divide.S + * + * (C) 1995 Linus Torvalds + * + * Alpha division.. + */ + +/* + * The alpha chip doesn't provide hardware division, so we have to do it + * by hand. The compiler expects the functions + * + * __divqu: 64-bit unsigned long divide + * __remqu: 64-bit unsigned long remainder + * __divqs/__remqs: signed 64-bit + * __divlu/__remlu: unsigned 32-bit + * __divls/__remls: signed 32-bit + * + * These are not normal C functions: instead of the normal + * calling sequence, these expect their arguments in registers + * $24 and $25, and return the result in $27. Register $28 may + * be clobbered (assembly temporary), anything else must be saved. + * + * In short: painful. + * + * This is a rather simple bit-at-a-time algorithm: it's very good + * at dividing random 64-bit numbers, but the more usual case where + * the divisor is small is handled better by the DEC algorithm + * using lookup tables. This uses much less memory, though, and is + * nicer on the cache.. Besides, I don't know the copyright status + * of the DEC code. + */ + +/* + * My temporaries: + * $0 - current bit + * $1 - shifted divisor + * $2 - modulus/quotient + * + * $23 - return address + * $24 - dividend + * $25 - divisor + * + * $27 - quotient/modulus + * $28 - compare status + */ + +#include +#define halt .long 0 + +/* + * Select function type and registers + */ +#define mask $0 +#define divisor $1 +#define compare $28 +#define tmp1 $3 +#define tmp2 $4 + +#ifdef DIV +#define DIV_ONLY(x,y...) x,##y +#define MOD_ONLY(x,y...) +#define func(x) __div##x +#define modulus $2 +#define quotient $27 +#define GETSIGN(x) xor $24,$25,x +#define STACK 48 +#else +#define DIV_ONLY(x,y...) +#define MOD_ONLY(x,y...) x,##y +#define func(x) __rem##x +#define modulus $27 +#define quotient $2 +#define GETSIGN(x) bis $24,$24,x +#define STACK 32 +#endif + +/* + * For 32-bit operations, we need to extend to 64-bit + */ +#ifdef INTSIZE +#define ufunction func(lu) +#define sfunction func(l) +#define LONGIFY(x) zapnot x,15,x +#define SLONGIFY(x) addl x,0,x +#else +#define ufunction func(qu) +#define sfunction func(q) +#define LONGIFY(x) +#define SLONGIFY(x) +#endif + +.set noat +.align 3 +.globl ufunction +.ent ufunction +ufunction: + subq $30,STACK,$30 + .frame $30,STACK,$23 + .prologue 0 + +7: stq $1, 0($30) + bis $25,$25,divisor + stq $2, 8($30) + bis $24,$24,modulus + stq $0,16($30) + bis $31,$31,quotient + LONGIFY(divisor) + stq tmp1,24($30) + LONGIFY(modulus) + bis $31,1,mask + DIV_ONLY(stq tmp2,32($30)) + beq divisor, 9f /* div by zero */ + +#ifdef INTSIZE + /* + * shift divisor left, using 3-bit shifts for + * 32-bit divides as we can't overflow. Three-bit + * shifts will result in looping three times less + * here, but can result in two loops more later. + * Thus using a large shift isn't worth it (and + * s8add pairs better than a sll..) + */ +1: cmpult divisor,modulus,compare + s8addq divisor,$31,divisor + s8addq mask,$31,mask + bne compare,1b +#else +1: cmpult divisor,modulus,compare + blt divisor, 2f + addq divisor,divisor,divisor + addq mask,mask,mask + bne compare,1b + unop +#endif + + /* ok, start to go right again.. */ +2: DIV_ONLY(addq quotient,mask,tmp2) + srl mask,1,mask + cmpule divisor,modulus,compare + subq modulus,divisor,tmp1 + DIV_ONLY(cmovne compare,tmp2,quotient) + srl divisor,1,divisor + cmovne compare,tmp1,modulus + bne mask,2b + +9: ldq $1, 0($30) + ldq $2, 8($30) + ldq $0,16($30) + ldq tmp1,24($30) + DIV_ONLY(ldq tmp2,32($30)) + addq $30,STACK,$30 + ret $31,($23),1 + .end ufunction +EXPORT_SYMBOL(ufunction) + +/* + * Uhh.. Ugly signed division. I'd rather not have it at all, but + * it's needed in some circumstances. There are different ways to + * handle this, really. This does: + * -a / b = a / -b = -(a / b) + * -a % b = -(a % b) + * a % -b = a % b + * which is probably not the best solution, but at least should + * have the property that (x/y)*y + (x%y) = x. + */ +.align 3 +.globl sfunction +.ent sfunction +sfunction: + subq $30,STACK,$30 + .frame $30,STACK,$23 + .prologue 0 + bis $24,$25,$28 + SLONGIFY($28) + bge $28,7b + stq $24,0($30) + subq $31,$24,$28 + stq $25,8($30) + cmovlt $24,$28,$24 /* abs($24) */ + stq $23,16($30) + subq $31,$25,$28 + stq tmp1,24($30) + cmovlt $25,$28,$25 /* abs($25) */ + unop + bsr $23,ufunction + ldq $24,0($30) + ldq $25,8($30) + GETSIGN($28) + subq $31,$27,tmp1 + SLONGIFY($28) + ldq $23,16($30) + cmovlt $28,tmp1,$27 + ldq tmp1,24($30) + addq $30,STACK,$30 + ret $31,($23),1 + .end sfunction +EXPORT_SYMBOL(sfunction) -- cgit v1.3.1