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/arc/lib/strcmp.S | 93 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 93 insertions(+) create mode 100644 arch/arc/lib/strcmp.S (limited to 'arch/arc/lib/strcmp.S') diff --git a/arch/arc/lib/strcmp.S b/arch/arc/lib/strcmp.S new file mode 100644 index 000000000..b20c98fb3 --- /dev/null +++ b/arch/arc/lib/strcmp.S @@ -0,0 +1,93 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) + */ + +/* This is optimized primarily for the ARC700. + It would be possible to speed up the loops by one cycle / word + respective one cycle / byte by forcing double source 1 alignment, unrolling + by a factor of two, and speculatively loading the second word / byte of + source 1; however, that would increase the overhead for loop setup / finish, + and strcmp might often terminate early. */ + +#include + +ENTRY_CFI(strcmp) + or r2,r0,r1 + bmsk_s r2,r2,1 + brne r2,0,.Lcharloop + mov_s r12,0x01010101 + ror r5,r12 +.Lwordloop: + ld.ab r2,[r0,4] + ld.ab r3,[r1,4] + nop_s + sub r4,r2,r12 + bic r4,r4,r2 + and r4,r4,r5 + brne r4,0,.Lfound0 + breq r2,r3,.Lwordloop +#ifdef __LITTLE_ENDIAN__ + xor r0,r2,r3 ; mask for difference + sub_s r1,r0,1 + bic_s r0,r0,r1 ; mask for least significant difference bit + sub r1,r5,r0 + xor r0,r5,r1 ; mask for least significant difference byte + and_s r2,r2,r0 + and_s r3,r3,r0 +#endif /* LITTLE ENDIAN */ + cmp_s r2,r3 + mov_s r0,1 + j_s.d [blink] + bset.lo r0,r0,31 + + .balign 4 +#ifdef __LITTLE_ENDIAN__ +.Lfound0: + xor r0,r2,r3 ; mask for difference + or r0,r0,r4 ; or in zero indicator + sub_s r1,r0,1 + bic_s r0,r0,r1 ; mask for least significant difference bit + sub r1,r5,r0 + xor r0,r5,r1 ; mask for least significant difference byte + and_s r2,r2,r0 + and_s r3,r3,r0 + sub.f r0,r2,r3 + mov.hi r0,1 + j_s.d [blink] + bset.lo r0,r0,31 +#else /* BIG ENDIAN */ + /* The zero-detection above can mis-detect 0x01 bytes as zeroes + because of carry-propagateion from a lower significant zero byte. + We can compensate for this by checking that bit0 is zero. + This compensation is not necessary in the step where we + get a low estimate for r2, because in any affected bytes + we already have 0x00 or 0x01, which will remain unchanged + when bit 7 is cleared. */ + .balign 4 +.Lfound0: + lsr r0,r4,8 + lsr_s r1,r2 + bic_s r2,r2,r0 ; get low estimate for r2 and get ... + bic_s r0,r0,r1 ; + or_s r3,r3,r0 ; ... high estimate r3 so that r2 > r3 will ... + cmp_s r3,r2 ; ... be independent of trailing garbage + or_s r2,r2,r0 ; likewise for r3 > r2 + bic_s r3,r3,r0 + rlc r0,0 ; r0 := r2 > r3 ? 1 : 0 + cmp_s r2,r3 + j_s.d [blink] + bset.lo r0,r0,31 +#endif /* ENDIAN */ + + .balign 4 +.Lcharloop: + ldb.ab r2,[r0,1] + ldb.ab r3,[r1,1] + nop_s + breq r2,0,.Lcmpend + breq r2,r3,.Lcharloop +.Lcmpend: + j_s.d [blink] + sub r0,r2,r3 +END_CFI(strcmp) -- cgit v1.3.1