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, 214 insertions, 0 deletions

diff --git a/drivers/pinctrl/pinconf.h b/drivers/pinctrl/pinconf.h
new file mode 100644
index 000000000..fc2d6cce9
--- /dev/null
+++ b/drivers/pinctrl/pinconf.h
@@ -0,0 +1,214 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Internal interface between the core pin control system and the
+ * pin config portions
+ *
+ * Copyright (C) 2011 ST-Ericsson SA
+ * Written on behalf of Linaro for ST-Ericsson
+ * Based on bits of regulator core, gpio core and clk core
+ *
+ * Author: Linus Walleij <linus.walleij@linaro.org>
+ */
+
+#include <linux/errno.h>
+
+struct dentry;
+struct device_node;
+struct seq_file;
+
+struct pinctrl_dev;
+struct pinctrl_map;
+struct pinctrl_setting;
+
+#ifdef CONFIG_PINCONF
+
+int pinconf_check_ops(struct pinctrl_dev *pctldev);
+int pinconf_validate_map(const struct pinctrl_map *map, int i);
+int pinconf_map_to_setting(const struct pinctrl_map *map,
+			  struct pinctrl_setting *setting);
+void pinconf_free_setting(const struct pinctrl_setting *setting);
+int pinconf_apply_setting(const struct pinctrl_setting *setting);
+
+int pinconf_set_config(struct pinctrl_dev *pctldev, unsigned int pin,
+		       unsigned long *configs, size_t nconfigs);
+
+/*
+ * You will only be interested in these if you're using PINCONF
+ * so don't supply any stubs for these.
+ */
+int pin_config_get_for_pin(struct pinctrl_dev *pctldev, unsigned int pin,
+			   unsigned long *config);
+int pin_config_group_get(const char *dev_name, const char *pin_group,
+			 unsigned long *config);
+
+#else
+
+static inline int pinconf_check_ops(struct pinctrl_dev *pctldev)
+{
+	return 0;
+}
+
+static inline int pinconf_validate_map(const struct pinctrl_map *map, int i)
+{
+	return 0;
+}
+
+static inline int pinconf_map_to_setting(const struct pinctrl_map *map,
+			  struct pinctrl_setting *setting)
+{
+	return 0;
+}
+
+static inline void pinconf_free_setting(const struct pinctrl_setting *setting)
+{
+}
+
+static inline int pinconf_apply_setting(const struct pinctrl_setting *setting)
+{
+	return 0;
+}
+
+static inline int pinconf_set_config(struct pinctrl_dev *pctldev, unsigned int pin,
+				     unsigned long *configs, size_t nconfigs)
+{
+	return -ENOTSUPP;
+}
+
+static inline int pin_config_get_for_pin(struct pinctrl_dev *pctldev, unsigned int pin,
+			   unsigned long *config)
+{
+	return -ENOTSUPP;
+}
+
+#endif
+
+#if defined(CONFIG_PINCONF) && defined(CONFIG_DEBUG_FS)
+
+void pinconf_show_map(struct seq_file *s, const struct pinctrl_map *map);
+void pinconf_show_setting(struct seq_file *s,
+			  const struct pinctrl_setting *setting);
+void pinconf_init_device_debugfs(struct dentry *devroot,
+				 struct pinctrl_dev *pctldev);
+
+#else
+
+static inline void pinconf_show_map(struct seq_file *s,
+				    const struct pinctrl_map *map)
+{
+}
+
+static inline void pinconf_show_setting(struct seq_file *s,
+					const struct pinctrl_setting *setting)
+{
+}
+
+static inline void pinconf_init_device_debugfs(struct dentry *devroot,
+					       struct pinctrl_dev *pctldev)
+{
+}
+
+#endif
+
+/*
+ * The following functions are available if the driver uses the generic
+ * pin config.
+ */
+
+#if defined(CONFIG_GENERIC_PINCONF) && defined(CONFIG_DEBUG_FS)
+
+void pinconf_generic_dump_pins(struct pinctrl_dev *pctldev,
+			       struct seq_file *s, const char *gname,
+			       unsigned int pin);
+
+void pinconf_generic_dump_config(struct pinctrl_dev *pctldev,
+				 struct seq_file *s, unsigned long config);
+#else
+
+static inline void pinconf_generic_dump_pins(struct pinctrl_dev *pctldev,
+					     struct seq_file *s,
+					     const char *gname, unsigned int pin)
+{
+	return;
+}
+
+static inline void pinconf_generic_dump_config(struct pinctrl_dev *pctldev,
+					       struct seq_file *s,
+					       unsigned long config)
+{
+	return;
+}
+#endif
+
+#if defined(CONFIG_GENERIC_PINCONF) && defined(CONFIG_OF)
+int pinconf_generic_parse_dt_config(struct device_node *np,
+				    struct pinctrl_dev *pctldev,
+				    unsigned long **configs,
+				    unsigned int *nconfigs);
+
+int pinconf_generic_parse_dt_pinmux(struct device_node *np, struct device *dev,
+				    unsigned int **pid, unsigned int **pmux,
+				    unsigned int *npins);
+#else
+static inline int
+pinconf_generic_parse_dt_config(struct device_node *np,
+				struct pinctrl_dev *pctldev,
+				unsigned long **configs,
+				unsigned int *nconfigs)
+{
+	return -ENOTSUPP;
+}
+
+static inline int
+pinconf_generic_parse_dt_pinmux(struct device_node *np, struct device *dev,
+				unsigned int **pid, unsigned int **pmux,
+				unsigned int *npins)
+{
+	return -ENOTSUPP;
+}
+#endif
+
+#if defined(CONFIG_GENERIC_PINCTRL)
+int pinctrl_generic_pins_function_dt_node_to_map(struct pinctrl_dev *pctldev,
+						 struct device_node *np,
+						 struct pinctrl_map **maps,
+						 unsigned int *num_maps);
+
+int pinctrl_generic_pinmux_dt_node_to_map(struct pinctrl_dev *pctldev,
+					  struct device_node *np,
+					  struct pinctrl_map **maps,
+					  unsigned int *num_maps);
+
+int pinctrl_generic_to_map(struct pinctrl_dev *pctldev, struct device_node *parent,
+			   struct device_node *np, struct pinctrl_map **maps,
+			   unsigned int *num_maps, unsigned int *num_reserved_maps,
+			   const char **group_name, unsigned int ngroups,
+			   void *data, unsigned int *pins, unsigned int npins);
+#else
+static inline int
+pinctrl_generic_pins_function_dt_node_to_map(struct pinctrl_dev *pctldev,
+					     struct device_node *np,
+					     struct pinctrl_map **maps,
+					     unsigned int *num_maps)
+{
+	return -ENOTSUPP;
+}
+
+static inline int
+pinctrl_generic_pinmux_dt_node_to_map(struct pinctrl_dev *pctldev,
+				      struct device_node *np,
+				      struct pinctrl_map **maps,
+				      unsigned int *num_maps)
+{
+	return -ENOTSUPP;
+}
+
+static inline int
+pinctrl_generic_to_map(struct pinctrl_dev *pctldev, struct device_node *parent,
+		       struct device_node *np, struct pinctrl_map **maps,
+		       unsigned int *num_maps, unsigned int *num_reserved_maps,
+		       const char **group_name, unsigned int ngroups,
+		       void *data, unsigned int *pins, unsigned int npins)
+{
+	return -ENOTSUPP;
+}
+#endif