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>

4 files changed, 162 insertions, 0 deletions

diff --git a/samples/acrn/Makefile b/samples/acrn/Makefile
new file mode 100644
index 000000000..c8e3ed978
--- /dev/null
+++ b/samples/acrn/Makefile
@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: GPL-2.0
+
+.PHONY: vm-sample
+
+vm-sample: vm-sample.o payload.o
+	$(CC) $^ -o $@
+
+payload.o: payload.ld guest16.o
+	$(LD) -T $< -o $@
+
+clean:
+	rm *.o vm-sample
diff --git a/samples/acrn/guest.ld b/samples/acrn/guest.ld
new file mode 100644
index 000000000..5127c682b
--- /dev/null
+++ b/samples/acrn/guest.ld
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+OUTPUT_FORMAT(binary)
+SECTIONS
+{
+        .start : { *(.start) }
+        .text : { *(.text*) }
+        .rodata : { *(.rodata) }
+        .data : { *(.data) }
+}
diff --git a/samples/acrn/payload.ld b/samples/acrn/payload.ld
new file mode 100644
index 000000000..e8d9a498a
--- /dev/null
+++ b/samples/acrn/payload.ld
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+SECTIONS
+{
+        .payload16 0 : {
+                guest16 = .;
+                guest16.o(.text)
+                guest16_end = .;
+        }
+}
diff --git a/samples/acrn/vm-sample.c b/samples/acrn/vm-sample.c
new file mode 100644
index 000000000..c61e0f914
--- /dev/null
+++ b/samples/acrn/vm-sample.c
@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * A sample program to run a User VM on the ACRN hypervisor
+ *
+ * This sample runs in a Service VM, which is a privileged VM of ACRN.
+ * CONFIG_ACRN_HSM needs to be enabled in the Service VM.
+ *
+ * Guest VM code in guest16.s will be executed after the VM launched.
+ *
+ * Copyright (C) 2020 Intel Corporation. All rights reserved.
+ */
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <signal.h>
+#include <sys/ioctl.h>
+#include <linux/acrn.h>
+
+#define GUEST_MEMORY_SIZE	(1024*1024)
+void *guest_memory;
+
+extern const unsigned char guest16[], guest16_end[];
+static char io_request_page[4096] __attribute__((aligned(4096)));
+static struct acrn_io_request *io_req_buf = (struct acrn_io_request *)io_request_page;
+
+__u16 vcpu_num;
+__u16 vmid;
+
+int hsm_fd;
+int is_running = 1;
+
+void vm_exit(int sig)
+{
+	sig = sig;
+
+	is_running = 0;
+	ioctl(hsm_fd, ACRN_IOCTL_PAUSE_VM, vmid);
+	ioctl(hsm_fd, ACRN_IOCTL_DESTROY_IOREQ_CLIENT, 0);
+}
+
+int main(int argc, char **argv)
+{
+	int vcpu_id, ret;
+	struct acrn_vm_creation create_vm = {0};
+	struct acrn_vm_memmap ram_map = {0};
+	struct acrn_vcpu_regs regs;
+	struct acrn_io_request *io_req;
+	struct acrn_ioreq_notify __attribute__((aligned(8))) notify;
+
+	argc = argc;
+	argv = argv;
+
+	ret = posix_memalign(&guest_memory, 4096, GUEST_MEMORY_SIZE);
+	if (ret < 0) {
+		printf("Not enough memory!\n");
+		return -1;
+	}
+	hsm_fd = open("/dev/acrn_hsm", O_RDWR|O_CLOEXEC);
+
+	create_vm.ioreq_buf = (__u64)io_req_buf;
+	ret = ioctl(hsm_fd, ACRN_IOCTL_CREATE_VM, &create_vm);
+	printf("Created VM! [%d]\n", ret);
+	vcpu_num = create_vm.vcpu_num;
+	vmid = create_vm.vmid;
+
+	/* setup guest memory */
+	ram_map.type = ACRN_MEMMAP_RAM;
+	ram_map.vma_base = (__u64)guest_memory;
+	ram_map.len = GUEST_MEMORY_SIZE;
+	ram_map.user_vm_pa = 0;
+	ram_map.attr = ACRN_MEM_ACCESS_RWX;
+	ret = ioctl(hsm_fd, ACRN_IOCTL_SET_MEMSEG, &ram_map);
+	printf("Set up VM memory! [%d]\n", ret);
+
+	memcpy(guest_memory, guest16, guest16_end-guest16);
+
+	/* setup vcpu registers */
+	memset(&regs, 0, sizeof(regs));
+	regs.vcpu_id = 0;
+	regs.vcpu_regs.rip = 0;
+
+	/* CR0_ET | CR0_NE */
+	regs.vcpu_regs.cr0 = 0x30U;
+	regs.vcpu_regs.cs_ar = 0x009FU;
+	regs.vcpu_regs.cs_sel = 0xF000U;
+	regs.vcpu_regs.cs_limit = 0xFFFFU;
+	regs.vcpu_regs.cs_base = 0 & 0xFFFF0000UL;
+	regs.vcpu_regs.rip = 0 & 0xFFFFUL;
+
+	ret = ioctl(hsm_fd, ACRN_IOCTL_SET_VCPU_REGS, &regs);
+	printf("Set up VM BSP registers! [%d]\n", ret);
+
+	/* create an ioreq client for this VM */
+	ret = ioctl(hsm_fd, ACRN_IOCTL_CREATE_IOREQ_CLIENT, 0);
+	printf("Created IO request client! [%d]\n", ret);
+
+	/* run vm */
+	ret = ioctl(hsm_fd, ACRN_IOCTL_START_VM, vmid);
+	printf("Start VM! [%d]\n", ret);
+
+	signal(SIGINT, vm_exit);
+	while (is_running) {
+		ret = ioctl(hsm_fd, ACRN_IOCTL_ATTACH_IOREQ_CLIENT, 0);
+
+		for (vcpu_id = 0; vcpu_id < vcpu_num; vcpu_id++) {
+			io_req = &io_req_buf[vcpu_id];
+			if ((__sync_add_and_fetch(&io_req->processed, 0) == ACRN_IOREQ_STATE_PROCESSING)
+					&& (!io_req->kernel_handled))
+				if (io_req->type == ACRN_IOREQ_TYPE_PORTIO) {
+					int bytes, port, in;
+
+					port = io_req->reqs.pio_request.address;
+					bytes = io_req->reqs.pio_request.size;
+					in = (io_req->reqs.pio_request.direction == ACRN_IOREQ_DIR_READ);
+					printf("Guest VM %s PIO[%x] with size[%x]\n", in ? "read" : "write", port, bytes);
+
+					notify.vmid = vmid;
+					notify.vcpu = vcpu_id;
+					ioctl(hsm_fd, ACRN_IOCTL_NOTIFY_REQUEST_FINISH, &notify);
+				}
+		}
+	}
+
+	ret = ioctl(hsm_fd, ACRN_IOCTL_DESTROY_VM, NULL);
+	printf("Destroy VM! [%d]\n", ret);
+	close(hsm_fd);
+	free(guest_memory);
+	return 0;
+}