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, 306 insertions, 0 deletions

diff --git a/drivers/bcma/driver_pci.c b/drivers/bcma/driver_pci.c
new file mode 100644
index 000000000..12b2cc9a3
--- /dev/null
+++ b/drivers/bcma/driver_pci.c
@@ -0,0 +1,306 @@
+/*
+ * Broadcom specific AMBA
+ * PCI Core
+ *
+ * Copyright 2005, 2011, Broadcom Corporation
+ * Copyright 2006, 2007, Michael Buesch <m@bues.ch>
+ * Copyright 2011, 2012, Hauke Mehrtens <hauke@hauke-m.de>
+ *
+ * Licensed under the GNU/GPL. See COPYING for details.
+ */
+
+#include "bcma_private.h"
+#include <linux/export.h>
+#include <linux/bcma/bcma.h>
+
+/**************************************************
+ * R/W ops.
+ **************************************************/
+
+u32 bcma_pcie_read(struct bcma_drv_pci *pc, u32 address)
+{
+	pcicore_write32(pc, BCMA_CORE_PCI_PCIEIND_ADDR, address);
+	pcicore_read32(pc, BCMA_CORE_PCI_PCIEIND_ADDR);
+	return pcicore_read32(pc, BCMA_CORE_PCI_PCIEIND_DATA);
+}
+
+static void bcma_pcie_write(struct bcma_drv_pci *pc, u32 address, u32 data)
+{
+	pcicore_write32(pc, BCMA_CORE_PCI_PCIEIND_ADDR, address);
+	pcicore_read32(pc, BCMA_CORE_PCI_PCIEIND_ADDR);
+	pcicore_write32(pc, BCMA_CORE_PCI_PCIEIND_DATA, data);
+}
+
+static void bcma_pcie_mdio_set_phy(struct bcma_drv_pci *pc, u16 phy)
+{
+	u32 v;
+	int i;
+
+	v = BCMA_CORE_PCI_MDIODATA_START;
+	v |= BCMA_CORE_PCI_MDIODATA_WRITE;
+	v |= (BCMA_CORE_PCI_MDIODATA_DEV_ADDR <<
+	      BCMA_CORE_PCI_MDIODATA_DEVADDR_SHF);
+	v |= (BCMA_CORE_PCI_MDIODATA_BLK_ADDR <<
+	      BCMA_CORE_PCI_MDIODATA_REGADDR_SHF);
+	v |= BCMA_CORE_PCI_MDIODATA_TA;
+	v |= (phy << 4);
+	pcicore_write32(pc, BCMA_CORE_PCI_MDIO_DATA, v);
+
+	udelay(10);
+	for (i = 0; i < 200; i++) {
+		v = pcicore_read32(pc, BCMA_CORE_PCI_MDIO_CONTROL);
+		if (v & BCMA_CORE_PCI_MDIOCTL_ACCESS_DONE)
+			break;
+		usleep_range(1000, 2000);
+	}
+}
+
+static u16 bcma_pcie_mdio_read(struct bcma_drv_pci *pc, u16 device, u8 address)
+{
+	int max_retries = 10;
+	u16 ret = 0;
+	u32 v;
+	int i;
+
+	/* enable mdio access to SERDES */
+	v = BCMA_CORE_PCI_MDIOCTL_PREAM_EN;
+	v |= BCMA_CORE_PCI_MDIOCTL_DIVISOR_VAL;
+	pcicore_write32(pc, BCMA_CORE_PCI_MDIO_CONTROL, v);
+
+	if (pc->core->id.rev >= 10) {
+		max_retries = 200;
+		bcma_pcie_mdio_set_phy(pc, device);
+		v = (BCMA_CORE_PCI_MDIODATA_DEV_ADDR <<
+		     BCMA_CORE_PCI_MDIODATA_DEVADDR_SHF);
+		v |= (address << BCMA_CORE_PCI_MDIODATA_REGADDR_SHF);
+	} else {
+		v = (device << BCMA_CORE_PCI_MDIODATA_DEVADDR_SHF_OLD);
+		v |= (address << BCMA_CORE_PCI_MDIODATA_REGADDR_SHF_OLD);
+	}
+
+	v |= BCMA_CORE_PCI_MDIODATA_START;
+	v |= BCMA_CORE_PCI_MDIODATA_READ;
+	v |= BCMA_CORE_PCI_MDIODATA_TA;
+
+	pcicore_write32(pc, BCMA_CORE_PCI_MDIO_DATA, v);
+	/* Wait for the device to complete the transaction */
+	udelay(10);
+	for (i = 0; i < max_retries; i++) {
+		v = pcicore_read32(pc, BCMA_CORE_PCI_MDIO_CONTROL);
+		if (v & BCMA_CORE_PCI_MDIOCTL_ACCESS_DONE) {
+			udelay(10);
+			ret = pcicore_read32(pc, BCMA_CORE_PCI_MDIO_DATA);
+			break;
+		}
+		usleep_range(1000, 2000);
+	}
+	pcicore_write32(pc, BCMA_CORE_PCI_MDIO_CONTROL, 0);
+	return ret;
+}
+
+static void bcma_pcie_mdio_write(struct bcma_drv_pci *pc, u16 device,
+				u8 address, u16 data)
+{
+	int max_retries = 10;
+	u32 v;
+	int i;
+
+	/* enable mdio access to SERDES */
+	v = BCMA_CORE_PCI_MDIOCTL_PREAM_EN;
+	v |= BCMA_CORE_PCI_MDIOCTL_DIVISOR_VAL;
+	pcicore_write32(pc, BCMA_CORE_PCI_MDIO_CONTROL, v);
+
+	if (pc->core->id.rev >= 10) {
+		max_retries = 200;
+		bcma_pcie_mdio_set_phy(pc, device);
+		v = (BCMA_CORE_PCI_MDIODATA_DEV_ADDR <<
+		     BCMA_CORE_PCI_MDIODATA_DEVADDR_SHF);
+		v |= (address << BCMA_CORE_PCI_MDIODATA_REGADDR_SHF);
+	} else {
+		v = (device << BCMA_CORE_PCI_MDIODATA_DEVADDR_SHF_OLD);
+		v |= (address << BCMA_CORE_PCI_MDIODATA_REGADDR_SHF_OLD);
+	}
+
+	v |= BCMA_CORE_PCI_MDIODATA_START;
+	v |= BCMA_CORE_PCI_MDIODATA_WRITE;
+	v |= BCMA_CORE_PCI_MDIODATA_TA;
+	v |= data;
+	pcicore_write32(pc, BCMA_CORE_PCI_MDIO_DATA, v);
+	/* Wait for the device to complete the transaction */
+	udelay(10);
+	for (i = 0; i < max_retries; i++) {
+		v = pcicore_read32(pc, BCMA_CORE_PCI_MDIO_CONTROL);
+		if (v & BCMA_CORE_PCI_MDIOCTL_ACCESS_DONE)
+			break;
+		usleep_range(1000, 2000);
+	}
+	pcicore_write32(pc, BCMA_CORE_PCI_MDIO_CONTROL, 0);
+}
+
+static u16 bcma_pcie_mdio_writeread(struct bcma_drv_pci *pc, u16 device,
+				    u8 address, u16 data)
+{
+	bcma_pcie_mdio_write(pc, device, address, data);
+	return bcma_pcie_mdio_read(pc, device, address);
+}
+
+/**************************************************
+ * Early init.
+ **************************************************/
+
+static void bcma_core_pci_fixcfg(struct bcma_drv_pci *pc)
+{
+	struct bcma_device *core = pc->core;
+	u16 val16, core_index;
+	uint regoff;
+
+	regoff = BCMA_CORE_PCI_SPROM(BCMA_CORE_PCI_SPROM_PI_OFFSET);
+	core_index = (u16)core->core_index;
+
+	val16 = pcicore_read16(pc, regoff);
+	if (((val16 & BCMA_CORE_PCI_SPROM_PI_MASK) >> BCMA_CORE_PCI_SPROM_PI_SHIFT)
+	     != core_index) {
+		val16 = (core_index << BCMA_CORE_PCI_SPROM_PI_SHIFT) |
+			(val16 & ~BCMA_CORE_PCI_SPROM_PI_MASK);
+		pcicore_write16(pc, regoff, val16);
+	}
+}
+
+/*
+ * Apply some early fixes required before accessing SPROM.
+ * See also si_pci_fixcfg.
+ */
+void bcma_core_pci_early_init(struct bcma_drv_pci *pc)
+{
+	if (pc->early_setup_done)
+		return;
+
+	pc->hostmode = bcma_core_pci_is_in_hostmode(pc);
+	if (pc->hostmode)
+		goto out;
+
+	bcma_core_pci_fixcfg(pc);
+
+out:
+	pc->early_setup_done = true;
+}
+
+/**************************************************
+ * Workarounds.
+ **************************************************/
+
+static u8 bcma_pcicore_polarity_workaround(struct bcma_drv_pci *pc)
+{
+	u32 tmp;
+
+	tmp = bcma_pcie_read(pc, BCMA_CORE_PCI_PLP_STATUSREG);
+	if (tmp & BCMA_CORE_PCI_PLP_POLARITYINV_STAT)
+		return BCMA_CORE_PCI_SERDES_RX_CTRL_FORCE |
+		       BCMA_CORE_PCI_SERDES_RX_CTRL_POLARITY;
+	else
+		return BCMA_CORE_PCI_SERDES_RX_CTRL_FORCE;
+}
+
+static void bcma_pcicore_serdes_workaround(struct bcma_drv_pci *pc)
+{
+	u16 tmp;
+
+	bcma_pcie_mdio_write(pc, BCMA_CORE_PCI_MDIODATA_DEV_RX,
+	                     BCMA_CORE_PCI_SERDES_RX_CTRL,
+			     bcma_pcicore_polarity_workaround(pc));
+	tmp = bcma_pcie_mdio_read(pc, BCMA_CORE_PCI_MDIODATA_DEV_PLL,
+	                          BCMA_CORE_PCI_SERDES_PLL_CTRL);
+	if (tmp & BCMA_CORE_PCI_PLL_CTRL_FREQDET_EN)
+		bcma_pcie_mdio_write(pc, BCMA_CORE_PCI_MDIODATA_DEV_PLL,
+		                     BCMA_CORE_PCI_SERDES_PLL_CTRL,
+		                     tmp & ~BCMA_CORE_PCI_PLL_CTRL_FREQDET_EN);
+}
+
+/* Fix MISC config to allow coming out of L2/L3-Ready state w/o PRST */
+/* Needs to happen when coming out of 'standby'/'hibernate' */
+static void bcma_core_pci_config_fixup(struct bcma_drv_pci *pc)
+{
+	u16 val16;
+	uint regoff;
+
+	regoff = BCMA_CORE_PCI_SPROM(BCMA_CORE_PCI_SPROM_MISC_CONFIG);
+
+	val16 = pcicore_read16(pc, regoff);
+
+	if (!(val16 & BCMA_CORE_PCI_SPROM_L23READY_EXIT_NOPERST)) {
+		val16 |= BCMA_CORE_PCI_SPROM_L23READY_EXIT_NOPERST;
+		pcicore_write16(pc, regoff, val16);
+	}
+}
+
+/**************************************************
+ * Init.
+ **************************************************/
+
+static void bcma_core_pci_clientmode_init(struct bcma_drv_pci *pc)
+{
+	bcma_pcicore_serdes_workaround(pc);
+	bcma_core_pci_config_fixup(pc);
+}
+
+void bcma_core_pci_init(struct bcma_drv_pci *pc)
+{
+	if (pc->setup_done)
+		return;
+
+	bcma_core_pci_early_init(pc);
+
+	if (pc->hostmode)
+		bcma_core_pci_hostmode_init(pc);
+	else
+		bcma_core_pci_clientmode_init(pc);
+}
+
+void bcma_core_pci_power_save(struct bcma_bus *bus, bool up)
+{
+	struct bcma_drv_pci *pc;
+	u16 data;
+
+	if (bus->hosttype != BCMA_HOSTTYPE_PCI)
+		return;
+
+	pc = &bus->drv_pci[0];
+
+	if (pc->core->id.rev >= 15 && pc->core->id.rev <= 20) {
+		data = up ? 0x74 : 0x7C;
+		bcma_pcie_mdio_writeread(pc, BCMA_CORE_PCI_MDIO_BLK1,
+					 BCMA_CORE_PCI_MDIO_BLK1_MGMT1, 0x7F64);
+		bcma_pcie_mdio_writeread(pc, BCMA_CORE_PCI_MDIO_BLK1,
+					 BCMA_CORE_PCI_MDIO_BLK1_MGMT3, data);
+	} else if (pc->core->id.rev >= 21 && pc->core->id.rev <= 22) {
+		data = up ? 0x75 : 0x7D;
+		bcma_pcie_mdio_writeread(pc, BCMA_CORE_PCI_MDIO_BLK1,
+					 BCMA_CORE_PCI_MDIO_BLK1_MGMT1, 0x7E65);
+		bcma_pcie_mdio_writeread(pc, BCMA_CORE_PCI_MDIO_BLK1,
+					 BCMA_CORE_PCI_MDIO_BLK1_MGMT3, data);
+	}
+}
+EXPORT_SYMBOL_GPL(bcma_core_pci_power_save);
+
+static void bcma_core_pci_extend_L1timer(struct bcma_drv_pci *pc, bool extend)
+{
+	u32 w;
+
+	w = bcma_pcie_read(pc, BCMA_CORE_PCI_DLLP_PMTHRESHREG);
+	if (extend)
+		w |= BCMA_CORE_PCI_ASPMTIMER_EXTEND;
+	else
+		w &= ~BCMA_CORE_PCI_ASPMTIMER_EXTEND;
+	bcma_pcie_write(pc, BCMA_CORE_PCI_DLLP_PMTHRESHREG, w);
+	bcma_pcie_read(pc, BCMA_CORE_PCI_DLLP_PMTHRESHREG);
+}
+
+void bcma_core_pci_up(struct bcma_drv_pci *pc)
+{
+	bcma_core_pci_extend_L1timer(pc, true);
+}
+
+void bcma_core_pci_down(struct bcma_drv_pci *pc)
+{
+	bcma_core_pci_extend_L1timer(pc, false);
+}