[5/10] libs/libc/elf: Load an FDPIC object.

arch/Kconfig

@@ -724,6 +724,13 @@ config ARCH_HAVE_ELF_EXECUTABLE
 	bool
 	default n
 
+config ARCH_HAVE_ELF_FDPIC
+	bool
+	default n
+	---help---
+		The architecture has a PIC base register and the ELF relocations
+		that an FDPIC object uses.
+
 config ARCH_HAVE_TRUSTZONE
 	bool
 	default n

arch/arm/Kconfig

@@ -1096,6 +1096,7 @@ config ARCH_ARMV7M
 	default n
 	select ARCH_HAVE_CPUINFO
 	select ARCH_HAVE_DEBUG
+	select ARCH_HAVE_ELF_FDPIC
 	select ARCH_HAVE_PERF_EVENTS
 
 config ARCH_CORTEXM3
@@ -1245,6 +1246,7 @@ config ARCH_ARMV8M
 	default n
 	select ARCH_HAVE_CPUINFO
 	select ARCH_HAVE_DEBUG
+	select ARCH_HAVE_ELF_FDPIC
 	select ARCH_HAVE_PERF_EVENTS
 
 config ARCH_CORTEXM23

arch/arm/include/arch.h

@@ -79,6 +79,45 @@ do { \
   ); \
 } while (0)
 
+#ifdef CONFIG_FDPIC
+
+/****************************************************************************
+ * Name: up_fdpic_invoke
+ *
+ * Description:
+ *   Call a module entry point with the module data base in the PIC base
+ *   register.  Put the caller data base back after the call.
+ *
+ * Input Parameters:
+ *   entry - The code address to enter.
+ *   arg   - The one word argument, passed in r0.
+ *   got   - The module data base to install.
+ *
+ ****************************************************************************/
+
+static inline void up_fdpic_invoke(uintptr_t entry, uintptr_t arg,
+                                   uintptr_t got)
+{
+  register uintptr_t r0v __asm__ ("r0") = arg;
+
+  /* arg is already in r0.  r4 goes on the stack with the PIC register to
+   * keep the push aligned to 8 bytes.
+   */
+
+  __asm__ __volatile__
+  (
+    "push {r4, " PIC_REG_STRING "}\n"   /* Save the caller's base       */
+    "mov " PIC_REG_STRING ", %[got]\n"  /* Install the module's base    */
+    "blx %[entry]\n"                    /* Enter the module             */
+    "pop {r4, " PIC_REG_STRING "}\n"    /* Restore the caller's base    */
+    : "+r" (r0v)
+    : [entry] "r" (entry), [got] "r" (got)
+    : "r1", "r2", "r3", "r12", "lr", "cc", "memory"
+  );
+}
+
+#endif /* CONFIG_FDPIC */
+
 #endif /* CONFIG_PIC */
 
 #ifdef CONFIG_ARCH_ADDRENV

arch/arm/include/elf.h

@@ -206,6 +206,18 @@
 #define R_ARM_THM_TLS_DESCSEQ16  129           /* Thumb16 */
 #define R_ARM_THM_TLS_DESCSEQ32  130           /* Thumb32 */
 
+/* FDPIC relocations.  Values from the ARM FDPIC ABI as implemented by
+ * binutils (include/elf/arm.h).
+ */
+
+#define R_ARM_GOTFUNCDESC        161           /* Data      GOT entry holding a descriptor */
+#define R_ARM_GOTOFFFUNCDESC     162           /* Data      GOT-relative descriptor */
+#define R_ARM_FUNCDESC           163           /* Data      Address of a descriptor */
+#define R_ARM_FUNCDESC_VALUE     164           /* Data      The descriptor itself: {code, GOT} */
+#define R_ARM_TLS_GD32_FDPIC     165           /* Data */
+#define R_ARM_TLS_LDM32_FDPIC    166           /* Data */
+#define R_ARM_TLS_IE32_FDPIC     167           /* Data */
+
 /* Processor specific values for the Phdr p_type field.  */
 
 #define PT_ARM_EXIDX             (PT_LOPROC + 1) /* ARM unwind segment.  */

binfmt/Kconfig

@@ -60,6 +60,38 @@ config ELF_STACKSIZE
 	default DEFAULT_TASK_STACKSIZE
 	---help---
 		This is the default stack size that will be used when starting ELF binaries.
+
+config FDPIC
+	bool "FDPIC modules"
+	default n
+	select PIC
+	depends on ARCH_HAVE_ELF_FDPIC
+	---help---
+		Load ELF modules built for the FDPIC ABI.
+
+		An FDPIC module places its read-only and writable segments
+		independently, so its text can be executed directly out of flash
+		while only the writable segment is copied to RAM, once per running
+		instance.  A filesystem that can show its media, such as XIPFS or
+		ROMFS, gives that result.  On any other filesystem the loader copies
+		the text to RAM, and the module runs but shares nothing.
+
+		Building a module needs an arm-uclinuxfdpiceabi linker.  The stock
+		arm-none-eabi compiler emits correct FDPIC objects for both C and
+		C++, so only the link needs it.
+
+		What this adds over the position independent ELF support already
+		present is a function pointer that carries its own data base, as a
+		two word descriptor rather than a bare code address.  That is what
+		lets a module be called back on a thread it did not create, such as
+		the work queue worker that runs a SIGEV_THREAD notification.
+
+		Selecting this makes ten libc and sched entry points that can
+		accept a callback from a module resolve such a descriptor before
+		storing or branching to it.  Each costs a register read and a
+		branch on a path that is not hot.
+
+		FDPIC is specified only for ARM Thumb-2.
 endif
 endif
 

include/elf.h

@@ -149,6 +149,7 @@
 #define ELFOSABI_MODESTO   11    /* Novell Modesto.  */
 #define ELFOSABI_OPENBSD   12    /* OpenBSD.  */
 #define ELFOSABI_ARM_AEABI 64    /* ARM EABI */
+#define ELFOSABI_ARM_FDPIC 65    /* ARM FDPIC */
 #define ELFOSABI_ARM       97    /* ARM */
 #define ELFOSABI_STANDALONE 255  /* Standalone (embedded) application */
 
@@ -278,6 +279,12 @@
 #define DT_TEXTREL         22         /* d_un=ignored */
 #define DT_JMPREL          23         /* d_un=d_ptr */
 #define DT_BINDNOW         24         /* d_un=ignored */
+#define DT_INIT_ARRAY      25         /* d_un=d_ptr */
+#define DT_FINI_ARRAY      26         /* d_un=d_ptr */
+#define DT_INIT_ARRAYSZ    27         /* d_un=d_val */
+#define DT_FINI_ARRAYSZ    28         /* d_un=d_val */
+#define DT_PREINIT_ARRAY   32         /* d_un=d_ptr */
+#define DT_PREINIT_ARRAYSZ 33         /* d_un=d_val */
 #define DT_LOPROC          0x70000000 /* d_un=unspecified */
 #define DT_HIPROC          0x7fffffff /* d_un= unspecified */
 

include/nuttx/fdpic.h

@@ -0,0 +1,129 @@
+/****************************************************************************
+ * include/nuttx/fdpic.h
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+#ifndef __INCLUDE_NUTTX_FDPIC_H
+#define __INCLUDE_NUTTX_FDPIC_H
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <stdint.h>
+
+#include <nuttx/arch.h>
+#include <nuttx/compiler.h>
+
+/****************************************************************************
+ * Public Types
+ ****************************************************************************/
+
+/* A function descriptor: what a function pointer is under FDPIC.  The
+ * firmware branches to a code address; a module passes one of these.
+ */
+
+struct fdpic_desc_s
+{
+  uintptr_t entry;      /* Address of the code */
+  uintptr_t got;        /* Data base to install before branching */
+};
+
+/****************************************************************************
+ * Inline Functions
+ ****************************************************************************/
+
+#ifdef CONFIG_FDPIC
+
+/****************************************************************************
+ * Name: fdpic_base
+ *
+ * Description:
+ *   The data base of the calling context, from the PIC base register.
+ *   Non-zero means the caller is an FDPIC module, zero means firmware.
+ *
+ ****************************************************************************/
+
+static inline uintptr_t fdpic_base(void)
+{
+  uintptr_t base;
+
+  up_getpicbase(&base);
+  return base;
+}
+
+/****************************************************************************
+ * Name: fdpic_callback
+ *
+ * Description:
+ *   Resolve a function pointer from a caller that may be an FDPIC module.
+ *   Only the entry point is taken: the data base is already in the register.
+ *
+ * Input Parameters:
+ *   fn - The pointer as it was received.
+ *
+ * Returned Value:
+ *   An address that can be branched to directly.
+ *
+ ****************************************************************************/
+
+static inline FAR void *fdpic_callback(FAR void *fn)
+{
+  if (fn != NULL && fdpic_base() != 0)
+    {
+      return (FAR void *)((FAR struct fdpic_desc_s *)fn)->entry;
+    }
+
+  return fn;
+}
+
+/****************************************************************************
+ * Name: fdpic_invoke
+ *
+ * Description:
+ *   Call a resolved module entry point with the module data base in the PIC
+ *   base register.  For a callback that runs on a shared thread, which
+ *   carries no module base.  Elsewhere fdpic_callback() is enough.
+ *
+ * Input Parameters:
+ *   entry - The code address to enter, already resolved from the descriptor.
+ *   arg   - The one word argument.
+ *   got   - The module data base to install.
+ *
+ ****************************************************************************/
+
+static inline void fdpic_invoke(uintptr_t entry, uintptr_t arg,
+                                uintptr_t got)
+{
+  up_fdpic_invoke(entry, arg, got);
+}
+
+#else
+
+#  define fdpic_base()       (0)
+#  define fdpic_callback(fn) (fn)
+#  define fdpic_invoke(entry, arg, got) \
+          ((void)(got), (((CODE void (*)(uintptr_t))(uintptr_t)(entry))(arg)))
+
+#endif /* CONFIG_FDPIC */
+
+#endif /* __INCLUDE_NUTTX_FDPIC_H */

include/nuttx/lib/elf.h

@@ -44,6 +44,15 @@
 #  define CONFIG_LIBC_ELF_MAXDEPEND  0
 #endif
 
+/* A compacting filesystem gives its media address with a pin that holds the
+ * blocks in place.  The loader holds the pin through a file reference,
+ * because the unload runs on another task.  Flat build only.
+ */
+
+#if defined(CONFIG_FS_XIPFS) && defined(CONFIG_BUILD_FLAT)
+#  define HAVE_LIBC_ELF_PIN 1
+#endif
+
 #ifndef CONFIG_LIBC_ELF_ALIGN_LOG2
 #  define CONFIG_LIBC_ELF_ALIGN_LOG2 2
 #endif
@@ -123,6 +132,7 @@ typedef CODE int (*mod_uninitializer_t)(FAR void *arg);
  *   nexports      - The number of symbols in the exported symbol table.
  */
 
+struct file;
 struct symtab_s;
 struct mod_info_s
 {
@@ -252,6 +262,36 @@ struct mod_loadinfo_s
                               * skip the copy.
                               */
 
+  /* FDPIC state.
+   *
+   * fdpic   - True if e_ident[EI_OSABI] marked this an FDPIC object.
+   * textpin - True if a filesystem pin holds the read-only segment, which
+   *           the loader gives back at unload.
+   */
+
+  bool          fdpic;
+  bool          textpin;
+
+#ifdef HAVE_LIBC_ELF_PIN
+  /* The file the pin is held through, handed to the module once it loads. */
+
+  FAR struct file *pinfile;
+#endif
+
+  /* The object's data base, from DT_PLTGOT.  An FDPIC module runs with this
+   * in the PIC base register.
+   */
+
+  uintptr_t     gotaddr;
+
+  /* Pool of function descriptors behind the writable segment.  Reserved
+   * when the segment is sized, and bounded by the relocation count.
+   */
+
+  uintptr_t     descpool;
+  uint16_t      ndesc;       /* Capacity */
+  uint16_t      usedesc;     /* Next free slot */
+
   /* Address environment.
    *
    * addrenv - This is the handle created by addrenv_allocate() that can be