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nuttx/arch/arm/include/elf.h
Marco Casaroli ea78802f8d binfmt/fdpic: Add an FDPIC ELF module loader. 
Lets a NOMMU target execute downloadable modules in place from
memory-mapped NOR flash, so a module's text and rodata never consume
RAM.  It is the consumer of xipfs: the loader maps a module's read-only
segment with MAP_XIP_STRICT, which resolves to a direct flash pointer or
fails with -ENXIO rather than falling back to a RAM copy, and pins the
extent for as long as the module is loaded so the defragmenter cannot
relocate code that is executing.

Only the writable segment is copied to RAM, once per running instance.
The loader follows DT_NEEDED so a module can use shared libraries, each
object getting its own GOT and its own data.

FDPIC is what makes this possible: text is position-independent and each
LOAD segment is placed independently, with the text-to-data offset
communicated at load time through function descriptors and the GOT.  A
descriptor is a pair -- entry pointer plus data base -- so a module
function handed back to the firmware carries the data base it needs.
r9 holds that base at runtime, per the ARM FDPIC ABI.

Reserving r9 across the base firmware is what allows a firmware routine
to call back into module code and still arrive with the module's data
base intact.  Toolchain.defs puts --fixed-r9 in ARCHCPUFLAGS rather than
CFLAGS, because almost every board Make.defs assigns CFLAGS with ':='
after including it, which would discard the flag; ARCHCPUFLAGS is
re-expanded by that same assignment and so survives it.  The CONFIG_PIC
--fixed-r10 case is skipped under FDPIC, since reserving both registers
would cost one for nothing.

The DT_NEEDED walk is depth capped.  fdpic_loaddepends() recursed once per
link of a dependency chain with a path buffer on each frame and nothing to
stop it, so a malformed module set overflowed the stack of whichever task
called the loader instead of being rejected.  A dependency *cycle* was never
the hazard -- an object joins the load's list before its own dependencies are
walked, so a library naming something already loaded finds it there and stops
-- what was unbounded is a chain of distinct names, which the list cannot
bound, hence an explicit cap rather than cycle detection.

A module's .rofixup section is skipped, and the file header records why.
.rofixup is the FDPIC self-relocation list a static executable's crt0 walks
to derive its own GOT when no loader is present.  A module links -shared
-nostartfiles, so no crt0 runs, and the built objects hold exactly one entry
there -- the address of the GOT itself, which this loader computes and
installs at every entry into module code anyway.

Assisted-by: Claude Code:claude-opus-5
Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com>
2026-08-01 12:23:27 +02:00

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/****************************************************************************
* arch/arm/include/elf.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.
*
****************************************************************************/
/* Reference: "ELF for the ARM Architecture," ARM IHI 0044D, current through
* ABI release 2.08, October 28, 2009, ARM Limited.
*/
#ifndef __ARCH_ARM_INCLUDE_ELF_H
#define __ARCH_ARM_INCLUDE_ELF_H
/****************************************************************************
* Pre-processor Prototypes
****************************************************************************/
/* 4.3.1 ELF Identification. Should have:
*
* e_machine = EM_ARM
* e_ident[EI_CLASS] = ELFCLASS32
* e_ident[EI_DATA] = ELFDATA2LSB (little endian) or
* ELFDATA2MSB (big endian)
*/
#define EM_ARCH EM_ARM
/* Table 4-2, ARM-specific e_flags */
#define EF_ARM_EABI_MASK 0xff000000
#define EF_ARM_EABI_UNKNOWN 0x00000000
#define EF_ARM_EABI_VER1 0x01000000
#define EF_ARM_EABI_VER2 0x02000000
#define EF_ARM_EABI_VER3 0x03000000
#define EF_ARM_EABI_VER4 0x04000000
#define EF_ARM_EABI_VER5 0x05000000
#define EF_ARM_BE8 0x00800000
#define EF_ARM_ABI_FLOAT_SOFT 0x00000200
#define EF_ARM_ABI_FLOAT_HARD 0x00000400
#ifdef __VFP_FP__
# ifdef __ARM_PCS_VFP
# define EF_ARM_ABI_FLOAT EF_ARM_ABI_FLOAT_HARD
# else
# define EF_ARM_ABI_FLOAT EF_ARM_ABI_FLOAT_SOFT
# endif
#else
# define EF_ARM_ABI_FLOAT 0
#endif
#define EF_FLAG (EF_ARM_EABI_VER5 | EF_ARM_ABI_FLOAT)
/* Table 4-4, Processor specific section types */
#define SHT_ARM_EXIDX 0x70000001 /* Exception Index table */
#define SHT_ARM_PREEMPTMAP 0x70000002 /* BPABI DLL dynamic linking pre-emption map */
#define SHT_ARM_ATTRIBUTES 0x70000003 /* Object file compatibility attributes */
#define SHT_ARM_DEBUGOVERLAY 0x70000004
#define SHT_ARM_OVERLAYSECTION 0x70000005
/* 4.7.1 Relocation codes
*
* S (when used on its own) is the address of the symbol.
* A is the addend for the relocation.
* P is the address of the place being relocated (derived from r_offset).
* Pa is the adjusted address of the place being relocated, defined as
* (P & 0xFFFFFFFC).
* T is 1 if the target symbol S has type STT_FUNC and the symbol addresses
* a Thumb instruction; it is 0 otherwise.
* B(S) is the addressing origin of the output segment defining the symbol S.
* GOT_ORG is the addressing origin of the Global Offset Table
* GOT(S) is the address of the GOT entry for the symbol S.
*/
#define R_ARM_NONE 0 /* No relocation */
#define R_ARM_PC24 1 /* ARM ((S + A) | T) - P */
#define R_ARM_ABS32 2 /* Data (S + A) | T */
#define R_ARM_REL32 3 /* Data ((S + A) | T) - P */
#define R_ARM_LDR_PC_G0 4 /* ARM S + A - P */
#define R_ARM_ABS16 5 /* Data S + A */
#define R_ARM_ABS12 6 /* ARM S + A */
#define R_ARM_THM_ABS5 7 /* Thumb16 S + A */
#define R_ARM_ABS8 8 /* Data S + A */
#define R_ARM_SBREL32 9 /* Data ((S + A) | T) - B(S) */
#define R_ARM_THM_CALL 10 /* Thumb32 ((S + A) | T) - P */
#define R_ARM_THM_PC8 11 /* Thumb16 S + A - Pa */
#define R_ARM_BREL_ADJ 12 /* Data ?B(S) + A */
#define R_ARM_TLS_DESC 13 /* Data */
#define R_ARM_THM_SWI8 14 /* Obsolete */
#define R_ARM_XPC25 15 /* Obsolete */
#define R_ARM_THM_XPC22 16 /* Obsolete */
#define R_ARM_TLS_DTPMOD32 17 /* Data Module[S] */
#define R_ARM_TLS_DTPOFF32 18 /* Data S + A - TLS */
#define R_ARM_TLS_TPOFF32 19 /* Data S + A - tp */
#define R_ARM_COPY 20 /* Miscellaneous */
#define R_ARM_GLOB_DAT 21 /* Data (S + A) | T */
#define R_ARM_JUMP_SLOT 22 /* Data (S + A) | T */
#define R_ARM_RELATIVE 23 /* Data B(S) + A */
#define R_ARM_GOTOFF32 24 /* Data ((S + A) | T) - GOT_ORG */
#define R_ARM_BASE_PREL 25 /* Data B(S) + A - P */
#define R_ARM_GOT_BREL 26 /* Data GOT(S) + A - GOT_ORG */
#define R_ARM_PLT32 27 /* ARM ((S + A) | T) - P */
#define R_ARM_CALL 28 /* ARM ((S + A) | T) - P */
#define R_ARM_JUMP24 29 /* ARM ((S + A) | T) - P */
#define R_ARM_THM_JUMP24 30 /* Thumb32 ((S + A) | T) - P */
#define R_ARM_BASE_ABS 31 /* Data B(S) + A */
#define R_ARM_ALU_PCREL_7_0 32 /* Obsolete */
#define R_ARM_ALU_PCREL_15_8 33 /* Obsolete */
#define R_ARM_ALU_PCREL_23_15 34 /* Obsolete */
#define R_ARM_LDR_SBREL_11_0_NC 35 /* ARM S + A - B(S) */
#define R_ARM_ALU_SBREL_19_12_NC 36 /* ARM S + A - B(S) */
#define R_ARM_ALU_SBREL_27_20_CK 37 /* ARM S + A - B(S) */
#define R_ARM_TARGET1 38 /* Miscellaneous (S + A) | T or ((S + A) | T) - P */
#define R_ARM_SBREL31 39 /* Data ((S + A) | T) - B(S) */
#define R_ARM_V4BX 40 /* Miscellaneous */
#define R_ARM_TARGET2 41 /* Miscellaneous */
#define R_ARM_PREL31 42 /* Data ((S + A) | T) - P */
#define R_ARM_MOVW_ABS_NC 43 /* ARM (S + A) | T */
#define R_ARM_MOVT_ABS 44 /* ARM S + A */
#define R_ARM_MOVW_PREL_NC 45 /* ARM ((S + A) | T) - P */
#define R_ARM_MOVT_PREL 46 /* ARM S + A - P */
#define R_ARM_THM_MOVW_ABS_NC 47 /* Thumb32 (S + A) | T */
#define R_ARM_THM_MOVT_ABS 48 /* Thumb32 S + A */
#define R_ARM_THM_MOVW_PREL_NC 49 /* Thumb32 ((S + A) | T) - P */
#define R_ARM_THM_MOVT_PREL 50 /* Thumb32 S + A - P */
#define R_ARM_THM_JUMP19 51 /* Thumb32 ((S + A) | T) - P */
#define R_ARM_THM_JUMP6 52 /* Thumb16 S + A - P */
#define R_ARM_THM_ALU_PREL_11_0 53 /* Thumb32 ((S + A) | T) - Pa */
#define R_ARM_THM_PC12 54 /* Thumb32 S + A - Pa */
#define R_ARM_ABS32_NOI 55 /* Data S + A */
#define R_ARM_REL32_NOI 56 /* Data S + A - P */
#define R_ARM_ALU_PC_G0_NC 57 /* ARM ((S + A) | T) - P */
#define R_ARM_ALU_PC_G0 58 /* ARM ((S + A) | T) - P */
#define R_ARM_ALU_PC_G1_NC 59 /* ARM ((S + A) | T) - P */
#define R_ARM_ALU_PC_G1 60 /* ARM ((S + A) | T) - P */
#define R_ARM_ALU_PC_G2 61 /* ARM ((S + A) | T) - P */
#define R_ARM_LDR_PC_G1 62 /* ARM S + A - P */
#define R_ARM_LDR_PC_G2 63 /* ARM S + A - P */
#define R_ARM_LDRS_PC_G0 64 /* ARM S + A - P */
#define R_ARM_LDRS_PC_G1 65 /* ARM S + A - P */
#define R_ARM_LDRS_PC_G2 66 /* ARM S + A - P */
#define R_ARM_LDC_PC_G0 67 /* ARM S + A - P */
#define R_ARM_LDC_PC_G1 68 /* ARM S + A - P */
#define R_ARM_LDC_PC_G2 69 /* ARM S + A - P */
#define R_ARM_ALU_SB_G0_NC 70 /* ARM ((S + A) | T) - B(S) */
#define R_ARM_ALU_SB_G0 71 /* ARM ((S + A) | T) - B(S) */
#define R_ARM_ALU_SB_G1_NC 72 /* ARM ((S + A) | T) - B(S) */
#define R_ARM_ALU_SB_G1 73 /* ARM ((S + A) | T) - B(S) */
#define R_ARM_ALU_SB_G2 74 /* ARM ((S + A) | T) - B(S) */
#define R_ARM_LDR_SB_G0 75 /* ARM S + A - B(S) */
#define R_ARM_LDR_SB_G1 76 /* ARM S + A - B(S) */
#define R_ARM_LDR_SB_G2 77 /* ARM S + A - B(S) */
#define R_ARM_LDRS_SB_G0 78 /* ARM S + A - B(S) */
#define R_ARM_LDRS_SB_G1 79 /* ARM S + A - B(S) */
#define R_ARM_LDRS_SB_G2 80 /* ARM S + A - B(S) */
#define R_ARM_LDC_SB_G0 81 /* ARM S + A - B(S) */
#define R_ARM_LDC_SB_G1 82 /* ARM S + A - B(S) */
#define R_ARM_LDC_SB_G2 83 /* ARM S + A - B(S) */
#define R_ARM_MOVW_BREL_NC 84 /* ARM ((S + A) | T) - B(S) */
#define R_ARM_MOVT_BREL 85 /* ARM S + A - B(S) */
#define R_ARM_MOVW_BREL 86 /* ARM ((S + A) | T) - B(S) */
#define R_ARM_THM_MOVW_BREL_NC 87 /* Thumb32 ((S + A) | T) - B(S) */
#define R_ARM_THM_MOVT_BREL 88 /* Thumb32 S + A - B(S) */
#define R_ARM_THM_MOVW_BREL 89 /* Thumb32 ((S + A) | T) - B(S) */
#define R_ARM_TLS_GOTDESC 90 /* Data */
#define R_ARM_TLS_CALL 91 /* ARM */
#define R_ARM_TLS_DESCSEQ 92 /* ARM TLS relaxation */
#define R_ARM_THM_TLS_CALL 93 /* Thumb32 */
#define R_ARM_PLT32_ABS 94 /* Data PLT(S) + A */
#define R_ARM_GOT_ABS 95 /* Data GOT(S) + A */
#define R_ARM_GOT_PREL 96 /* Data GOT(S) + A - P */
#define R_ARM_GOT_BREL12 97 /* ARM GOT(S) + A - GOT_ORG */
#define R_ARM_GOTOFF12 98 /* ARM S + A - GOT_ORG */
#define R_ARM_GOTRELAX 99 /* Miscellaneous */
#define R_ARM_GNU_VTENTRY 100 /* Data */
#define R_ARM_GNU_VTINHERIT 101 /* Data */
#define R_ARM_THM_JUMP11 102 /* Thumb16 S + A - P */
#define R_ARM_THM_JUMP8 103 /* Thumb16 S + A - P */
#define R_ARM_TLS_GD32 104 /* Data GOT(S) + A - P */
#define R_ARM_TLS_LDM32 105 /* Data GOT(S) + A - P */
#define R_ARM_TLS_LDO32 106 /* Data S + A - TLS */
#define R_ARM_TLS_IE32 107 /* Data GOT(S) + A - P */
#define R_ARM_TLS_LE32 108 /* Data S + A - tp */
#define R_ARM_TLS_LDO12 109 /* ARM S + A - TLS */
#define R_ARM_TLS_LE12 110 /* ARM S + A - tp */
#define R_ARM_TLS_IE12GP 111 /* ARM GOT(S) + A - GOT_ORG */
#define R_ARM_ME_TOO 128 /* Obsolete */
#define R_ARM_THM_TLS_DESCSEQ16 129 /* Thumb16 */
#define R_ARM_THM_TLS_DESCSEQ32 130 /* Thumb32 */
/* FDPIC relocations.
*
* Under the FDPIC ABI each PT_LOAD segment is placed independently, so a
* function pointer cannot be a bare code address: it has to carry the data
* base its callee will need. A "function descriptor" is that pair, and
* these relocations are how the loader is asked to build and reference
* them. Values are 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. */
/* 5.2.1 Platform architecture compatibility data */
#define PT_ARM_ARCHEXT_FMTMSK 0xff000000
#define PT_ARM_ARCHEXT_PROFMSK 0x00ff0000
#define PT_ARM_ARCHEXT_ARCHMSK 0x000000ff
#define PT_ARM_ARCHEXT_FMT_OS 0x00000000
#define PT_ARM_ARCHEXT_FMT_ABI 0x01000000
#define PT_ARM_ARCHEXT_PROF_NONE 0x00000000
#define PT_ARM_ARCHEXT_PROF_ARM 0x00410000
#define PT_ARM_ARCHEXT_PROF_RT 0x00520000
#define PT_ARM_ARCHEXT_PROF_MC 0x004d0000
#define PT_ARM_ARCHEXT_PROF_CLASSIC 0x00530000
#define PT_ARM_ARCHEXT_ARCH_UNKNOWN 0x00
#define PT_ARM_ARCHEXT_ARCHv4 0x01
#define PT_ARM_ARCHEXT_ARCHv4T 0x02
#define PT_ARM_ARCHEXT_ARCHv5T 0x03
#define PT_ARM_ARCHEXT_ARCHv5TE 0x04
#define PT_ARM_ARCHEXT_ARCHv5TEJ 0x05
#define PT_ARM_ARCHEXT_ARCHv6 0x06
#define PT_ARM_ARCHEXT_ARCHv6KZ 0x07
#define PT_ARM_ARCHEXT_ARCHv6T2 0x08
#define PT_ARM_ARCHEXT_ARCHv6K 0x09
#define PT_ARM_ARCHEXT_ARCHv7 0x0a
#define PT_ARM_ARCHEXT_ARCHv6M 0x0b
#define PT_ARM_ARCHEXT_ARCHv6SM 0x0c
#define PT_ARM_ARCHEXT_ARCHv7EM 0x0d
/* Table 5-6, ARM-specific dynamic array tags */
#define DT_ARM_RESERVED1 0x70000000
#define DT_ARM_SYMTABSZ 0x70000001
#define DT_ARM_PREEMPTMAP 0x70000002
#define DT_ARM_RESERVED2 0x70000003
/****************************************************************************
* Public Types
****************************************************************************/
typedef struct __EIT_entry
{
unsigned long fnoffset;
unsigned long content;
} __EIT_entry;
/* ELF register definitions */
/* Holds the general purpose registers $a1 * through to $pc
* at indices 0 to 15. At index 16 the program status register.
* Index 17 should be set to zero.
*/
typedef unsigned long elf_gregset_t[18];
/****************************************************************************
* Public Data
****************************************************************************/
#ifdef __cplusplus
#define EXTERN extern "C"
extern "C"
{
#else
#define EXTERN extern
#endif
extern __EIT_entry __exidx_start[];
extern __EIT_entry __exidx_end[];
#undef EXTERN
#ifdef __cplusplus
}
#endif
#endif /* __ARCH_ARM_INCLUDE_ELF_H */
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