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, 353 insertions, 0 deletions

diff --git a/arch/mips/math-emu/me-debugfs.c b/arch/mips/math-emu/me-debugfs.c
new file mode 100644
index 000000000..aeddf7aec
--- /dev/null
+++ b/arch/mips/math-emu/me-debugfs.c
@@ -0,0 +1,353 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/cpumask.h>
+#include <linux/debugfs.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/percpu.h>
+#include <linux/types.h>
+#include <asm/debug.h>
+#include <asm/fpu_emulator.h>
+#include <asm/local.h>
+
+DEFINE_PER_CPU(struct mips_fpu_emulator_stats, fpuemustats);
+
+static int fpuemu_stat_get(void *data, u64 *val)
+{
+	int cpu;
+	unsigned long sum = 0;
+
+	for_each_online_cpu(cpu) {
+		struct mips_fpu_emulator_stats *ps;
+		local_t *pv;
+
+		ps = &per_cpu(fpuemustats, cpu);
+		pv = (void *)ps + (unsigned long)data;
+		sum += local_read(pv);
+	}
+	*val = sum;
+	return 0;
+}
+DEFINE_SIMPLE_ATTRIBUTE(fops_fpuemu_stat, fpuemu_stat_get, NULL, "%llu\n");
+
+/*
+ * Used to obtain names for a debugfs instruction counter, given field name
+ * in fpuemustats structure. For example, for input "cmp_sueq_d", the output
+ * would be "cmp.sueq.d". This is needed since dots are not allowed to be
+ * used in structure field names, and are, on the other hand, desired to be
+ * used in debugfs item names to be clearly associated to corresponding
+ * MIPS FPU instructions.
+ */
+static void adjust_instruction_counter_name(char *out_name, char *in_name, size_t len)
+{
+	int i = 0;
+
+	strscpy(out_name, in_name, len);
+	while (in_name[i] != '\0') {
+		if (out_name[i] == '_')
+			out_name[i] = '.';
+		i++;
+	}
+}
+
+static int fpuemustats_clear_show(struct seq_file *s, void *unused)
+{
+	__this_cpu_write((fpuemustats).emulated, 0);
+	__this_cpu_write((fpuemustats).loads, 0);
+	__this_cpu_write((fpuemustats).stores, 0);
+	__this_cpu_write((fpuemustats).branches, 0);
+	__this_cpu_write((fpuemustats).cp1ops, 0);
+	__this_cpu_write((fpuemustats).cp1xops, 0);
+	__this_cpu_write((fpuemustats).errors, 0);
+	__this_cpu_write((fpuemustats).ieee754_inexact, 0);
+	__this_cpu_write((fpuemustats).ieee754_underflow, 0);
+	__this_cpu_write((fpuemustats).ieee754_overflow, 0);
+	__this_cpu_write((fpuemustats).ieee754_zerodiv, 0);
+	__this_cpu_write((fpuemustats).ieee754_invalidop, 0);
+	__this_cpu_write((fpuemustats).ds_emul, 0);
+
+	__this_cpu_write((fpuemustats).abs_s, 0);
+	__this_cpu_write((fpuemustats).abs_d, 0);
+	__this_cpu_write((fpuemustats).add_s, 0);
+	__this_cpu_write((fpuemustats).add_d, 0);
+	__this_cpu_write((fpuemustats).bc1eqz, 0);
+	__this_cpu_write((fpuemustats).bc1nez, 0);
+	__this_cpu_write((fpuemustats).ceil_w_s, 0);
+	__this_cpu_write((fpuemustats).ceil_w_d, 0);
+	__this_cpu_write((fpuemustats).ceil_l_s, 0);
+	__this_cpu_write((fpuemustats).ceil_l_d, 0);
+	__this_cpu_write((fpuemustats).class_s, 0);
+	__this_cpu_write((fpuemustats).class_d, 0);
+	__this_cpu_write((fpuemustats).cmp_af_s, 0);
+	__this_cpu_write((fpuemustats).cmp_af_d, 0);
+	__this_cpu_write((fpuemustats).cmp_eq_s, 0);
+	__this_cpu_write((fpuemustats).cmp_eq_d, 0);
+	__this_cpu_write((fpuemustats).cmp_le_s, 0);
+	__this_cpu_write((fpuemustats).cmp_le_d, 0);
+	__this_cpu_write((fpuemustats).cmp_lt_s, 0);
+	__this_cpu_write((fpuemustats).cmp_lt_d, 0);
+	__this_cpu_write((fpuemustats).cmp_ne_s, 0);
+	__this_cpu_write((fpuemustats).cmp_ne_d, 0);
+	__this_cpu_write((fpuemustats).cmp_or_s, 0);
+	__this_cpu_write((fpuemustats).cmp_or_d, 0);
+	__this_cpu_write((fpuemustats).cmp_ueq_s, 0);
+	__this_cpu_write((fpuemustats).cmp_ueq_d, 0);
+	__this_cpu_write((fpuemustats).cmp_ule_s, 0);
+	__this_cpu_write((fpuemustats).cmp_ule_d, 0);
+	__this_cpu_write((fpuemustats).cmp_ult_s, 0);
+	__this_cpu_write((fpuemustats).cmp_ult_d, 0);
+	__this_cpu_write((fpuemustats).cmp_un_s, 0);
+	__this_cpu_write((fpuemustats).cmp_un_d, 0);
+	__this_cpu_write((fpuemustats).cmp_une_s, 0);
+	__this_cpu_write((fpuemustats).cmp_une_d, 0);
+	__this_cpu_write((fpuemustats).cmp_saf_s, 0);
+	__this_cpu_write((fpuemustats).cmp_saf_d, 0);
+	__this_cpu_write((fpuemustats).cmp_seq_s, 0);
+	__this_cpu_write((fpuemustats).cmp_seq_d, 0);
+	__this_cpu_write((fpuemustats).cmp_sle_s, 0);
+	__this_cpu_write((fpuemustats).cmp_sle_d, 0);
+	__this_cpu_write((fpuemustats).cmp_slt_s, 0);
+	__this_cpu_write((fpuemustats).cmp_slt_d, 0);
+	__this_cpu_write((fpuemustats).cmp_sne_s, 0);
+	__this_cpu_write((fpuemustats).cmp_sne_d, 0);
+	__this_cpu_write((fpuemustats).cmp_sor_s, 0);
+	__this_cpu_write((fpuemustats).cmp_sor_d, 0);
+	__this_cpu_write((fpuemustats).cmp_sueq_s, 0);
+	__this_cpu_write((fpuemustats).cmp_sueq_d, 0);
+	__this_cpu_write((fpuemustats).cmp_sule_s, 0);
+	__this_cpu_write((fpuemustats).cmp_sule_d, 0);
+	__this_cpu_write((fpuemustats).cmp_sult_s, 0);
+	__this_cpu_write((fpuemustats).cmp_sult_d, 0);
+	__this_cpu_write((fpuemustats).cmp_sun_s, 0);
+	__this_cpu_write((fpuemustats).cmp_sun_d, 0);
+	__this_cpu_write((fpuemustats).cmp_sune_s, 0);
+	__this_cpu_write((fpuemustats).cmp_sune_d, 0);
+	__this_cpu_write((fpuemustats).cvt_d_l, 0);
+	__this_cpu_write((fpuemustats).cvt_d_s, 0);
+	__this_cpu_write((fpuemustats).cvt_d_w, 0);
+	__this_cpu_write((fpuemustats).cvt_l_s, 0);
+	__this_cpu_write((fpuemustats).cvt_l_d, 0);
+	__this_cpu_write((fpuemustats).cvt_s_d, 0);
+	__this_cpu_write((fpuemustats).cvt_s_l, 0);
+	__this_cpu_write((fpuemustats).cvt_s_w, 0);
+	__this_cpu_write((fpuemustats).cvt_w_s, 0);
+	__this_cpu_write((fpuemustats).cvt_w_d, 0);
+	__this_cpu_write((fpuemustats).div_s, 0);
+	__this_cpu_write((fpuemustats).div_d, 0);
+	__this_cpu_write((fpuemustats).floor_w_s, 0);
+	__this_cpu_write((fpuemustats).floor_w_d, 0);
+	__this_cpu_write((fpuemustats).floor_l_s, 0);
+	__this_cpu_write((fpuemustats).floor_l_d, 0);
+	__this_cpu_write((fpuemustats).maddf_s, 0);
+	__this_cpu_write((fpuemustats).maddf_d, 0);
+	__this_cpu_write((fpuemustats).max_s, 0);
+	__this_cpu_write((fpuemustats).max_d, 0);
+	__this_cpu_write((fpuemustats).maxa_s, 0);
+	__this_cpu_write((fpuemustats).maxa_d, 0);
+	__this_cpu_write((fpuemustats).min_s, 0);
+	__this_cpu_write((fpuemustats).min_d, 0);
+	__this_cpu_write((fpuemustats).mina_s, 0);
+	__this_cpu_write((fpuemustats).mina_d, 0);
+	__this_cpu_write((fpuemustats).mov_s, 0);
+	__this_cpu_write((fpuemustats).mov_d, 0);
+	__this_cpu_write((fpuemustats).msubf_s, 0);
+	__this_cpu_write((fpuemustats).msubf_d, 0);
+	__this_cpu_write((fpuemustats).mul_s, 0);
+	__this_cpu_write((fpuemustats).mul_d, 0);
+	__this_cpu_write((fpuemustats).neg_s, 0);
+	__this_cpu_write((fpuemustats).neg_d, 0);
+	__this_cpu_write((fpuemustats).recip_s, 0);
+	__this_cpu_write((fpuemustats).recip_d, 0);
+	__this_cpu_write((fpuemustats).rint_s, 0);
+	__this_cpu_write((fpuemustats).rint_d, 0);
+	__this_cpu_write((fpuemustats).round_w_s, 0);
+	__this_cpu_write((fpuemustats).round_w_d, 0);
+	__this_cpu_write((fpuemustats).round_l_s, 0);
+	__this_cpu_write((fpuemustats).round_l_d, 0);
+	__this_cpu_write((fpuemustats).rsqrt_s, 0);
+	__this_cpu_write((fpuemustats).rsqrt_d, 0);
+	__this_cpu_write((fpuemustats).sel_s, 0);
+	__this_cpu_write((fpuemustats).sel_d, 0);
+	__this_cpu_write((fpuemustats).seleqz_s, 0);
+	__this_cpu_write((fpuemustats).seleqz_d, 0);
+	__this_cpu_write((fpuemustats).selnez_s, 0);
+	__this_cpu_write((fpuemustats).selnez_d, 0);
+	__this_cpu_write((fpuemustats).sqrt_s, 0);
+	__this_cpu_write((fpuemustats).sqrt_d, 0);
+	__this_cpu_write((fpuemustats).sub_s, 0);
+	__this_cpu_write((fpuemustats).sub_d, 0);
+	__this_cpu_write((fpuemustats).trunc_w_s, 0);
+	__this_cpu_write((fpuemustats).trunc_w_d, 0);
+	__this_cpu_write((fpuemustats).trunc_l_s, 0);
+	__this_cpu_write((fpuemustats).trunc_l_d, 0);
+
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(fpuemustats_clear);
+
+static int __init debugfs_fpuemu(void)
+{
+	struct dentry *fpuemu_debugfs_base_dir;
+	struct dentry *fpuemu_debugfs_inst_dir;
+	char name[32];
+
+	fpuemu_debugfs_base_dir = debugfs_create_dir("fpuemustats",
+						     mips_debugfs_dir);
+
+	debugfs_create_file("fpuemustats_clear", 0444, mips_debugfs_dir, NULL,
+			    &fpuemustats_clear_fops);
+
+#define FPU_EMU_STAT_OFFSET(m)						\
+	offsetof(struct mips_fpu_emulator_stats, m)
+
+#define FPU_STAT_CREATE(m)						\
+do {									\
+	debugfs_create_file(#m, 0444, fpuemu_debugfs_base_dir,		\
+				(void *)FPU_EMU_STAT_OFFSET(m),		\
+				&fops_fpuemu_stat);			\
+} while (0)
+
+	FPU_STAT_CREATE(emulated);
+	FPU_STAT_CREATE(loads);
+	FPU_STAT_CREATE(stores);
+	FPU_STAT_CREATE(branches);
+	FPU_STAT_CREATE(cp1ops);
+	FPU_STAT_CREATE(cp1xops);
+	FPU_STAT_CREATE(errors);
+	FPU_STAT_CREATE(ieee754_inexact);
+	FPU_STAT_CREATE(ieee754_underflow);
+	FPU_STAT_CREATE(ieee754_overflow);
+	FPU_STAT_CREATE(ieee754_zerodiv);
+	FPU_STAT_CREATE(ieee754_invalidop);
+	FPU_STAT_CREATE(ds_emul);
+
+	fpuemu_debugfs_inst_dir = debugfs_create_dir("instructions",
+						     fpuemu_debugfs_base_dir);
+
+#define FPU_STAT_CREATE_EX(m)						\
+do {									\
+	adjust_instruction_counter_name(name, #m, sizeof(name));			\
+									\
+	debugfs_create_file(name, 0444, fpuemu_debugfs_inst_dir,	\
+				(void *)FPU_EMU_STAT_OFFSET(m),		\
+				&fops_fpuemu_stat);			\
+} while (0)
+
+	FPU_STAT_CREATE_EX(abs_s);
+	FPU_STAT_CREATE_EX(abs_d);
+	FPU_STAT_CREATE_EX(add_s);
+	FPU_STAT_CREATE_EX(add_d);
+	FPU_STAT_CREATE_EX(bc1eqz);
+	FPU_STAT_CREATE_EX(bc1nez);
+	FPU_STAT_CREATE_EX(ceil_w_s);
+	FPU_STAT_CREATE_EX(ceil_w_d);
+	FPU_STAT_CREATE_EX(ceil_l_s);
+	FPU_STAT_CREATE_EX(ceil_l_d);
+	FPU_STAT_CREATE_EX(class_s);
+	FPU_STAT_CREATE_EX(class_d);
+	FPU_STAT_CREATE_EX(cmp_af_s);
+	FPU_STAT_CREATE_EX(cmp_af_d);
+	FPU_STAT_CREATE_EX(cmp_eq_s);
+	FPU_STAT_CREATE_EX(cmp_eq_d);
+	FPU_STAT_CREATE_EX(cmp_le_s);
+	FPU_STAT_CREATE_EX(cmp_le_d);
+	FPU_STAT_CREATE_EX(cmp_lt_s);
+	FPU_STAT_CREATE_EX(cmp_lt_d);
+	FPU_STAT_CREATE_EX(cmp_ne_s);
+	FPU_STAT_CREATE_EX(cmp_ne_d);
+	FPU_STAT_CREATE_EX(cmp_or_s);
+	FPU_STAT_CREATE_EX(cmp_or_d);
+	FPU_STAT_CREATE_EX(cmp_ueq_s);
+	FPU_STAT_CREATE_EX(cmp_ueq_d);
+	FPU_STAT_CREATE_EX(cmp_ule_s);
+	FPU_STAT_CREATE_EX(cmp_ule_d);
+	FPU_STAT_CREATE_EX(cmp_ult_s);
+	FPU_STAT_CREATE_EX(cmp_ult_d);
+	FPU_STAT_CREATE_EX(cmp_un_s);
+	FPU_STAT_CREATE_EX(cmp_un_d);
+	FPU_STAT_CREATE_EX(cmp_une_s);
+	FPU_STAT_CREATE_EX(cmp_une_d);
+	FPU_STAT_CREATE_EX(cmp_saf_s);
+	FPU_STAT_CREATE_EX(cmp_saf_d);
+	FPU_STAT_CREATE_EX(cmp_seq_s);
+	FPU_STAT_CREATE_EX(cmp_seq_d);
+	FPU_STAT_CREATE_EX(cmp_sle_s);
+	FPU_STAT_CREATE_EX(cmp_sle_d);
+	FPU_STAT_CREATE_EX(cmp_slt_s);
+	FPU_STAT_CREATE_EX(cmp_slt_d);
+	FPU_STAT_CREATE_EX(cmp_sne_s);
+	FPU_STAT_CREATE_EX(cmp_sne_d);
+	FPU_STAT_CREATE_EX(cmp_sor_s);
+	FPU_STAT_CREATE_EX(cmp_sor_d);
+	FPU_STAT_CREATE_EX(cmp_sueq_s);
+	FPU_STAT_CREATE_EX(cmp_sueq_d);
+	FPU_STAT_CREATE_EX(cmp_sule_s);
+	FPU_STAT_CREATE_EX(cmp_sule_d);
+	FPU_STAT_CREATE_EX(cmp_sult_s);
+	FPU_STAT_CREATE_EX(cmp_sult_d);
+	FPU_STAT_CREATE_EX(cmp_sun_s);
+	FPU_STAT_CREATE_EX(cmp_sun_d);
+	FPU_STAT_CREATE_EX(cmp_sune_s);
+	FPU_STAT_CREATE_EX(cmp_sune_d);
+	FPU_STAT_CREATE_EX(cvt_d_l);
+	FPU_STAT_CREATE_EX(cvt_d_s);
+	FPU_STAT_CREATE_EX(cvt_d_w);
+	FPU_STAT_CREATE_EX(cvt_l_s);
+	FPU_STAT_CREATE_EX(cvt_l_d);
+	FPU_STAT_CREATE_EX(cvt_s_d);
+	FPU_STAT_CREATE_EX(cvt_s_l);
+	FPU_STAT_CREATE_EX(cvt_s_w);
+	FPU_STAT_CREATE_EX(cvt_w_s);
+	FPU_STAT_CREATE_EX(cvt_w_d);
+	FPU_STAT_CREATE_EX(div_s);
+	FPU_STAT_CREATE_EX(div_d);
+	FPU_STAT_CREATE_EX(floor_w_s);
+	FPU_STAT_CREATE_EX(floor_w_d);
+	FPU_STAT_CREATE_EX(floor_l_s);
+	FPU_STAT_CREATE_EX(floor_l_d);
+	FPU_STAT_CREATE_EX(maddf_s);
+	FPU_STAT_CREATE_EX(maddf_d);
+	FPU_STAT_CREATE_EX(max_s);
+	FPU_STAT_CREATE_EX(max_d);
+	FPU_STAT_CREATE_EX(maxa_s);
+	FPU_STAT_CREATE_EX(maxa_d);
+	FPU_STAT_CREATE_EX(min_s);
+	FPU_STAT_CREATE_EX(min_d);
+	FPU_STAT_CREATE_EX(mina_s);
+	FPU_STAT_CREATE_EX(mina_d);
+	FPU_STAT_CREATE_EX(mov_s);
+	FPU_STAT_CREATE_EX(mov_d);
+	FPU_STAT_CREATE_EX(msubf_s);
+	FPU_STAT_CREATE_EX(msubf_d);
+	FPU_STAT_CREATE_EX(mul_s);
+	FPU_STAT_CREATE_EX(mul_d);
+	FPU_STAT_CREATE_EX(neg_s);
+	FPU_STAT_CREATE_EX(neg_d);
+	FPU_STAT_CREATE_EX(recip_s);
+	FPU_STAT_CREATE_EX(recip_d);
+	FPU_STAT_CREATE_EX(rint_s);
+	FPU_STAT_CREATE_EX(rint_d);
+	FPU_STAT_CREATE_EX(round_w_s);
+	FPU_STAT_CREATE_EX(round_w_d);
+	FPU_STAT_CREATE_EX(round_l_s);
+	FPU_STAT_CREATE_EX(round_l_d);
+	FPU_STAT_CREATE_EX(rsqrt_s);
+	FPU_STAT_CREATE_EX(rsqrt_d);
+	FPU_STAT_CREATE_EX(sel_s);
+	FPU_STAT_CREATE_EX(sel_d);
+	FPU_STAT_CREATE_EX(seleqz_s);
+	FPU_STAT_CREATE_EX(seleqz_d);
+	FPU_STAT_CREATE_EX(selnez_s);
+	FPU_STAT_CREATE_EX(selnez_d);
+	FPU_STAT_CREATE_EX(sqrt_s);
+	FPU_STAT_CREATE_EX(sqrt_d);
+	FPU_STAT_CREATE_EX(sub_s);
+	FPU_STAT_CREATE_EX(sub_d);
+	FPU_STAT_CREATE_EX(trunc_w_s);
+	FPU_STAT_CREATE_EX(trunc_w_d);
+	FPU_STAT_CREATE_EX(trunc_l_s);
+	FPU_STAT_CREATE_EX(trunc_l_d);
+
+	return 0;
+}
+arch_initcall(debugfs_fpuemu);