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, 429 insertions, 0 deletions

diff --git a/lib/iomap.c b/lib/iomap.c
new file mode 100644
index 000000000..a65717cd8
--- /dev/null
+++ b/lib/iomap.c
@@ -0,0 +1,429 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Implement the default iomap interfaces
+ *
+ * (C) Copyright 2004 Linus Torvalds
+ */
+#include <linux/pci.h>
+#include <linux/io.h>
+#include <linux/kmsan-checks.h>
+
+#include <linux/export.h>
+
+/*
+ * Read/write from/to an (offsettable) iomem cookie. It might be a PIO
+ * access or a MMIO access, these functions don't care. The info is
+ * encoded in the hardware mapping set up by the mapping functions
+ * (or the cookie itself, depending on implementation and hw).
+ *
+ * The generic routines don't assume any hardware mappings, and just
+ * encode the PIO/MMIO as part of the cookie. They coldly assume that
+ * the MMIO IO mappings are not in the low address range.
+ *
+ * Architectures for which this is not true can't use this generic
+ * implementation and should do their own copy.
+ */
+
+#ifndef HAVE_ARCH_PIO_SIZE
+/*
+ * We encode the physical PIO addresses (0-0xffff) into the
+ * pointer by offsetting them with a constant (0x10000) and
+ * assuming that all the low addresses are always PIO. That means
+ * we can do some sanity checks on the low bits, and don't
+ * need to just take things for granted.
+ */
+#define PIO_OFFSET	0x10000UL
+#define PIO_MASK	0x0ffffUL
+#define PIO_RESERVED	0x40000UL
+#endif
+
+static void bad_io_access(unsigned long port, const char *access)
+{
+	static int count = 10;
+	if (count) {
+		count--;
+		WARN(1, KERN_ERR "Bad IO access at port %#lx (%s)\n", port, access);
+	}
+}
+
+/*
+ * Ugly macros are a way of life.
+ */
+#define IO_COND(addr, is_pio, is_mmio) do {			\
+	unsigned long port = (unsigned long __force)addr;	\
+	if (port >= PIO_RESERVED) {				\
+		is_mmio;					\
+	} else if (port > PIO_OFFSET) {				\
+		port &= PIO_MASK;				\
+		is_pio;						\
+	} else							\
+		bad_io_access(port, #is_pio );			\
+} while (0)
+
+#ifndef pio_read16be
+#define pio_read16be(port) swab16(inw(port))
+#define pio_read32be(port) swab32(inl(port))
+#endif
+
+#ifndef mmio_read16be
+#define mmio_read16be(addr) swab16(readw(addr))
+#define mmio_read32be(addr) swab32(readl(addr))
+#define mmio_read64be(addr) swab64(readq(addr))
+#endif
+
+/*
+ * Here and below, we apply __no_kmsan_checks to functions reading data from
+ * hardware, to ensure that KMSAN marks their return values as initialized.
+ */
+__no_kmsan_checks
+unsigned int ioread8(const void __iomem *addr)
+{
+	IO_COND(addr, return inb(port), return readb(addr));
+	return 0xff;
+}
+__no_kmsan_checks
+unsigned int ioread16(const void __iomem *addr)
+{
+	IO_COND(addr, return inw(port), return readw(addr));
+	return 0xffff;
+}
+__no_kmsan_checks
+unsigned int ioread16be(const void __iomem *addr)
+{
+	IO_COND(addr, return pio_read16be(port), return mmio_read16be(addr));
+	return 0xffff;
+}
+__no_kmsan_checks
+unsigned int ioread32(const void __iomem *addr)
+{
+	IO_COND(addr, return inl(port), return readl(addr));
+	return 0xffffffff;
+}
+__no_kmsan_checks
+unsigned int ioread32be(const void __iomem *addr)
+{
+	IO_COND(addr, return pio_read32be(port), return mmio_read32be(addr));
+	return 0xffffffff;
+}
+EXPORT_SYMBOL(ioread8);
+EXPORT_SYMBOL(ioread16);
+EXPORT_SYMBOL(ioread16be);
+EXPORT_SYMBOL(ioread32);
+EXPORT_SYMBOL(ioread32be);
+
+#ifdef CONFIG_64BIT
+static u64 pio_read64_lo_hi(unsigned long port)
+{
+	u64 lo, hi;
+
+	lo = inl(port);
+	hi = inl(port + sizeof(u32));
+
+	return lo | (hi << 32);
+}
+
+static u64 pio_read64_hi_lo(unsigned long port)
+{
+	u64 lo, hi;
+
+	hi = inl(port + sizeof(u32));
+	lo = inl(port);
+
+	return lo | (hi << 32);
+}
+
+static u64 pio_read64be_lo_hi(unsigned long port)
+{
+	u64 lo, hi;
+
+	lo = pio_read32be(port + sizeof(u32));
+	hi = pio_read32be(port);
+
+	return lo | (hi << 32);
+}
+
+static u64 pio_read64be_hi_lo(unsigned long port)
+{
+	u64 lo, hi;
+
+	hi = pio_read32be(port);
+	lo = pio_read32be(port + sizeof(u32));
+
+	return lo | (hi << 32);
+}
+
+__no_kmsan_checks
+u64 __ioread64_lo_hi(const void __iomem *addr)
+{
+	IO_COND(addr, return pio_read64_lo_hi(port), return readq(addr));
+	return 0xffffffffffffffffULL;
+}
+
+__no_kmsan_checks
+u64 __ioread64_hi_lo(const void __iomem *addr)
+{
+	IO_COND(addr, return pio_read64_hi_lo(port), return readq(addr));
+	return 0xffffffffffffffffULL;
+}
+
+__no_kmsan_checks
+u64 __ioread64be_lo_hi(const void __iomem *addr)
+{
+	IO_COND(addr, return pio_read64be_lo_hi(port),
+		return mmio_read64be(addr));
+	return 0xffffffffffffffffULL;
+}
+
+__no_kmsan_checks
+u64 __ioread64be_hi_lo(const void __iomem *addr)
+{
+	IO_COND(addr, return pio_read64be_hi_lo(port),
+		return mmio_read64be(addr));
+	return 0xffffffffffffffffULL;
+}
+
+EXPORT_SYMBOL(__ioread64_lo_hi);
+EXPORT_SYMBOL(__ioread64_hi_lo);
+EXPORT_SYMBOL(__ioread64be_lo_hi);
+EXPORT_SYMBOL(__ioread64be_hi_lo);
+
+#endif /* CONFIG_64BIT */
+
+#ifndef pio_write16be
+#define pio_write16be(val,port) outw(swab16(val),port)
+#define pio_write32be(val,port) outl(swab32(val),port)
+#endif
+
+#ifndef mmio_write16be
+#define mmio_write16be(val,port) writew(swab16(val),port)
+#define mmio_write32be(val,port) writel(swab32(val),port)
+#define mmio_write64be(val,port) writeq(swab64(val),port)
+#endif
+
+void iowrite8(u8 val, void __iomem *addr)
+{
+	/* Make sure uninitialized memory isn't copied to devices. */
+	kmsan_check_memory(&val, sizeof(val));
+	IO_COND(addr, outb(val,port), writeb(val, addr));
+}
+void iowrite16(u16 val, void __iomem *addr)
+{
+	/* Make sure uninitialized memory isn't copied to devices. */
+	kmsan_check_memory(&val, sizeof(val));
+	IO_COND(addr, outw(val,port), writew(val, addr));
+}
+void iowrite16be(u16 val, void __iomem *addr)
+{
+	/* Make sure uninitialized memory isn't copied to devices. */
+	kmsan_check_memory(&val, sizeof(val));
+	IO_COND(addr, pio_write16be(val,port), mmio_write16be(val, addr));
+}
+void iowrite32(u32 val, void __iomem *addr)
+{
+	/* Make sure uninitialized memory isn't copied to devices. */
+	kmsan_check_memory(&val, sizeof(val));
+	IO_COND(addr, outl(val,port), writel(val, addr));
+}
+void iowrite32be(u32 val, void __iomem *addr)
+{
+	/* Make sure uninitialized memory isn't copied to devices. */
+	kmsan_check_memory(&val, sizeof(val));
+	IO_COND(addr, pio_write32be(val,port), mmio_write32be(val, addr));
+}
+EXPORT_SYMBOL(iowrite8);
+EXPORT_SYMBOL(iowrite16);
+EXPORT_SYMBOL(iowrite16be);
+EXPORT_SYMBOL(iowrite32);
+EXPORT_SYMBOL(iowrite32be);
+
+#ifdef CONFIG_64BIT
+static void pio_write64_lo_hi(u64 val, unsigned long port)
+{
+	outl(val, port);
+	outl(val >> 32, port + sizeof(u32));
+}
+
+static void pio_write64_hi_lo(u64 val, unsigned long port)
+{
+	outl(val >> 32, port + sizeof(u32));
+	outl(val, port);
+}
+
+static void pio_write64be_lo_hi(u64 val, unsigned long port)
+{
+	pio_write32be(val, port + sizeof(u32));
+	pio_write32be(val >> 32, port);
+}
+
+static void pio_write64be_hi_lo(u64 val, unsigned long port)
+{
+	pio_write32be(val >> 32, port);
+	pio_write32be(val, port + sizeof(u32));
+}
+
+void __iowrite64_lo_hi(u64 val, void __iomem *addr)
+{
+	/* Make sure uninitialized memory isn't copied to devices. */
+	kmsan_check_memory(&val, sizeof(val));
+	IO_COND(addr, pio_write64_lo_hi(val, port),
+		writeq(val, addr));
+}
+
+void __iowrite64_hi_lo(u64 val, void __iomem *addr)
+{
+	/* Make sure uninitialized memory isn't copied to devices. */
+	kmsan_check_memory(&val, sizeof(val));
+	IO_COND(addr, pio_write64_hi_lo(val, port),
+		writeq(val, addr));
+}
+
+void __iowrite64be_lo_hi(u64 val, void __iomem *addr)
+{
+	/* Make sure uninitialized memory isn't copied to devices. */
+	kmsan_check_memory(&val, sizeof(val));
+	IO_COND(addr, pio_write64be_lo_hi(val, port),
+		mmio_write64be(val, addr));
+}
+
+void __iowrite64be_hi_lo(u64 val, void __iomem *addr)
+{
+	/* Make sure uninitialized memory isn't copied to devices. */
+	kmsan_check_memory(&val, sizeof(val));
+	IO_COND(addr, pio_write64be_hi_lo(val, port),
+		mmio_write64be(val, addr));
+}
+
+EXPORT_SYMBOL(__iowrite64_lo_hi);
+EXPORT_SYMBOL(__iowrite64_hi_lo);
+EXPORT_SYMBOL(__iowrite64be_lo_hi);
+EXPORT_SYMBOL(__iowrite64be_hi_lo);
+
+#endif /* CONFIG_64BIT */
+
+/*
+ * These are the "repeat MMIO read/write" functions.
+ * Note the "__raw" accesses, since we don't want to
+ * convert to CPU byte order. We write in "IO byte
+ * order" (we also don't have IO barriers).
+ */
+#ifndef mmio_insb
+static inline void mmio_insb(const void __iomem *addr, u8 *dst, int count)
+{
+	while (--count >= 0) {
+		u8 data = __raw_readb(addr);
+		*dst = data;
+		dst++;
+	}
+}
+static inline void mmio_insw(const void __iomem *addr, u16 *dst, int count)
+{
+	while (--count >= 0) {
+		u16 data = __raw_readw(addr);
+		*dst = data;
+		dst++;
+	}
+}
+static inline void mmio_insl(const void __iomem *addr, u32 *dst, int count)
+{
+	while (--count >= 0) {
+		u32 data = __raw_readl(addr);
+		*dst = data;
+		dst++;
+	}
+}
+#endif
+
+#ifndef mmio_outsb
+static inline void mmio_outsb(void __iomem *addr, const u8 *src, int count)
+{
+	while (--count >= 0) {
+		__raw_writeb(*src, addr);
+		src++;
+	}
+}
+static inline void mmio_outsw(void __iomem *addr, const u16 *src, int count)
+{
+	while (--count >= 0) {
+		__raw_writew(*src, addr);
+		src++;
+	}
+}
+static inline void mmio_outsl(void __iomem *addr, const u32 *src, int count)
+{
+	while (--count >= 0) {
+		__raw_writel(*src, addr);
+		src++;
+	}
+}
+#endif
+
+void ioread8_rep(const void __iomem *addr, void *dst, unsigned long count)
+{
+	IO_COND(addr, insb(port,dst,count), mmio_insb(addr, dst, count));
+	/* KMSAN must treat values read from devices as initialized. */
+	kmsan_unpoison_memory(dst, count);
+}
+void ioread16_rep(const void __iomem *addr, void *dst, unsigned long count)
+{
+	IO_COND(addr, insw(port,dst,count), mmio_insw(addr, dst, count));
+	/* KMSAN must treat values read from devices as initialized. */
+	kmsan_unpoison_memory(dst, count * 2);
+}
+void ioread32_rep(const void __iomem *addr, void *dst, unsigned long count)
+{
+	IO_COND(addr, insl(port,dst,count), mmio_insl(addr, dst, count));
+	/* KMSAN must treat values read from devices as initialized. */
+	kmsan_unpoison_memory(dst, count * 4);
+}
+EXPORT_SYMBOL(ioread8_rep);
+EXPORT_SYMBOL(ioread16_rep);
+EXPORT_SYMBOL(ioread32_rep);
+
+void iowrite8_rep(void __iomem *addr, const void *src, unsigned long count)
+{
+	/* Make sure uninitialized memory isn't copied to devices. */
+	kmsan_check_memory(src, count);
+	IO_COND(addr, outsb(port, src, count), mmio_outsb(addr, src, count));
+}
+void iowrite16_rep(void __iomem *addr, const void *src, unsigned long count)
+{
+	/* Make sure uninitialized memory isn't copied to devices. */
+	kmsan_check_memory(src, count * 2);
+	IO_COND(addr, outsw(port, src, count), mmio_outsw(addr, src, count));
+}
+void iowrite32_rep(void __iomem *addr, const void *src, unsigned long count)
+{
+	/* Make sure uninitialized memory isn't copied to devices. */
+	kmsan_check_memory(src, count * 4);
+	IO_COND(addr, outsl(port, src,count), mmio_outsl(addr, src, count));
+}
+EXPORT_SYMBOL(iowrite8_rep);
+EXPORT_SYMBOL(iowrite16_rep);
+EXPORT_SYMBOL(iowrite32_rep);
+
+#ifdef CONFIG_HAS_IOPORT_MAP
+/* Create a virtual mapping cookie for an IO port range */
+void __iomem *ioport_map(unsigned long port, unsigned int nr)
+{
+	if (port > PIO_MASK)
+		return NULL;
+	return (void __iomem *) (unsigned long) (port + PIO_OFFSET);
+}
+
+void ioport_unmap(void __iomem *addr)
+{
+	/* Nothing to do */
+}
+EXPORT_SYMBOL(ioport_map);
+EXPORT_SYMBOL(ioport_unmap);
+#endif /* CONFIG_HAS_IOPORT_MAP */
+
+#ifdef CONFIG_PCI
+/* Hide the details if this is a MMIO or PIO address space and just do what
+ * you expect in the correct way. */
+void pci_iounmap(struct pci_dev *dev, void __iomem * addr)
+{
+	IO_COND(addr, /* nothing */, iounmap(addr));
+}
+EXPORT_SYMBOL(pci_iounmap);
+#endif /* CONFIG_PCI */