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/memcmp.S | 149 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 149 insertions(+) create mode 100644 arch/arc/lib/memcmp.S (limited to 'arch/arc/lib/memcmp.S') diff --git a/arch/arc/lib/memcmp.S b/arch/arc/lib/memcmp.S new file mode 100644 index 000000000..d6dc5e9bc --- /dev/null +++ b/arch/arc/lib/memcmp.S @@ -0,0 +1,149 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) + */ + +#include + +#ifdef __LITTLE_ENDIAN__ +#define WORD2 r2 +#define SHIFT r3 +#else /* BIG ENDIAN */ +#define WORD2 r3 +#define SHIFT r2 +#endif + +ENTRY_CFI(memcmp) + or r12,r0,r1 + asl_s r12,r12,30 + sub r3,r2,1 + brls r2,r12,.Lbytewise + ld r4,[r0,0] + ld r5,[r1,0] + lsr.f lp_count,r3,3 +#ifdef CONFIG_ISA_ARCV2 + /* In ARCv2 a branch can't be the last instruction in a zero overhead + * loop. + * So we move the branch to the start of the loop, duplicate it + * after the end, and set up r12 so that the branch isn't taken + * initially. + */ + mov_s r12,WORD2 + lpne .Loop_end + brne WORD2,r12,.Lodd + ld WORD2,[r0,4] +#else + lpne .Loop_end + ld_s WORD2,[r0,4] +#endif + ld_s r12,[r1,4] + brne r4,r5,.Leven + ld.a r4,[r0,8] + ld.a r5,[r1,8] +#ifdef CONFIG_ISA_ARCV2 +.Loop_end: + brne WORD2,r12,.Lodd +#else + brne WORD2,r12,.Lodd +.Loop_end: +#endif + asl_s SHIFT,SHIFT,3 + bhs_s .Last_cmp + brne r4,r5,.Leven + ld r4,[r0,4] + ld r5,[r1,4] +#ifdef __LITTLE_ENDIAN__ + nop_s + ; one more load latency cycle +.Last_cmp: + xor r0,r4,r5 + bset r0,r0,SHIFT + sub_s r1,r0,1 + bic_s r1,r1,r0 + norm r1,r1 + b.d .Leven_cmp + and r1,r1,24 +.Leven: + xor r0,r4,r5 + sub_s r1,r0,1 + bic_s r1,r1,r0 + norm r1,r1 + ; slow track insn + and r1,r1,24 +.Leven_cmp: + asl r2,r4,r1 + asl r12,r5,r1 + lsr_s r2,r2,1 + lsr_s r12,r12,1 + j_s.d [blink] + sub r0,r2,r12 + .balign 4 +.Lodd: + xor r0,WORD2,r12 + sub_s r1,r0,1 + bic_s r1,r1,r0 + norm r1,r1 + ; slow track insn + and r1,r1,24 + asl_s r2,r2,r1 + asl_s r12,r12,r1 + lsr_s r2,r2,1 + lsr_s r12,r12,1 + j_s.d [blink] + sub r0,r2,r12 +#else /* BIG ENDIAN */ +.Last_cmp: + neg_s SHIFT,SHIFT + lsr r4,r4,SHIFT + lsr r5,r5,SHIFT + ; slow track insn +.Leven: + sub.f r0,r4,r5 + mov.ne r0,1 + j_s.d [blink] + bset.cs r0,r0,31 +.Lodd: + cmp_s WORD2,r12 + mov_s r0,1 + j_s.d [blink] + bset.cs r0,r0,31 +#endif /* ENDIAN */ + .balign 4 +.Lbytewise: + breq r2,0,.Lnil + ldb r4,[r0,0] + ldb r5,[r1,0] + lsr.f lp_count,r3 +#ifdef CONFIG_ISA_ARCV2 + mov r12,r3 + lpne .Lbyte_end + brne r3,r12,.Lbyte_odd +#else + lpne .Lbyte_end +#endif + ldb_s r3,[r0,1] + ldb r12,[r1,1] + brne r4,r5,.Lbyte_even + ldb.a r4,[r0,2] + ldb.a r5,[r1,2] +#ifdef CONFIG_ISA_ARCV2 +.Lbyte_end: + brne r3,r12,.Lbyte_odd +#else + brne r3,r12,.Lbyte_odd +.Lbyte_end: +#endif + bcc .Lbyte_even + brne r4,r5,.Lbyte_even + ldb_s r3,[r0,1] + ldb_s r12,[r1,1] +.Lbyte_odd: + j_s.d [blink] + sub r0,r3,r12 +.Lbyte_even: + j_s.d [blink] + sub r0,r4,r5 +.Lnil: + j_s.d [blink] + mov r0,0 +END_CFI(memcmp) -- cgit v1.3.1