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nuttx/arch/arm/include/elf.h
Marco Casaroli 50a735bf86 libs/libc/machine/arm: Relocate FDPIC function descriptors. 
A function pointer under FDPIC is not a code address.  Because each
PT_LOAD segment is placed independently, a pointer has to carry the data
base its callee will need, so it is a two-word descriptor: the entry
point, and the base to install in the PIC register before branching.
R_ARM_FUNCDESC_VALUE says "the thing you are patching is such a
descriptor", and R_ARM_FUNCDESC says "manufacture one and give me its
address".

Both need state a relocation cannot carry.  A descriptor's second word is
the *object's* data base, from DT_PLTGOT, and R_ARM_FUNCDESC carves
descriptors from a pool whose cursor has to survive from one relocation
to the next.  up_relocate() is handed only a relocation, a resolved
symbol and an address to patch.

arch_data is the existing channel for exactly this -- RISC-V already uses
it to remember a HI20 relocation while its LO12 partner is processed --
but nothing has ever put loader state into it: it is declared zeroed and
written only by up_relocate() itself.  So ARCH_ELFDATA_INIT and
ARCH_ELFDATA_FINI are added, seeding the block from the loadinfo before
the relocation loop and reading the cursor back after.  Both default to
nothing, so an architecture that does not define them is unaffected, and
RISC-V's use of arch_data is untouched.  libelf_relocatedyn() walks both
dynamic tables under one arch_data, so the cursor spans the whole object.

The addend handling is the part that is easy to get wrong.  REL format
keeps the addend in place, in the word about to become the entry point,
and a pointer to a static function is referenced through its *section*
symbol -- the value is the section base and the offset, including the
Thumb bit, is entirely in the addend.  Dropping it yields an even address
and the core faults trying to execute it as ARM code.

The GOT written into a descriptor is the loading object's own, even for
an imported function, which is what makes a callback work: when the base
firmware's qsort() calls back into a module's comparison function, the
module needs its own data base in the PIC register.

libelf_relocatedyn()'s imported-symbol path needed a change to suit.  It
stores the resolved address directly and never calls up_relocate(), which
cannot produce a two-word descriptor, so under FDPIC the resolved value
now goes through up_relocate() and the relocation type decides what to
write.

Implemented for armv7-m and armv8-m, the profiles FDPIC targets; the
other ARM variants gain the arch_data block but no new relocations.
Built and booted mps3-an547:picostest and lm3s6965-ek:qemu-nxflat, the
ELF PIC and NXFLAT users of this code, both unchanged.

Assisted-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com>
2026-09-13 16:03:32 -03:00

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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
/* An object built for the FDPIC ABI says so in the OS/ABI byte. */
#define ELF_IS_FDPIC(ehdr) \
((ehdr)->e_ident[EI_OSABI] == ELFOSABI_ARM_FDPIC)
/* 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. 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. */
/* 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
/* Loader state the FDPIC relocations need: the object's data base, and the
* descriptor pool cursor, which must survive from one relocation to the
* next. It arrives through the arch_data channel.
*/
#define ARCH_ELFDATA 1
#define ARCH_ELFDATA_INIT(d, l) \
do \
{ \
(d)->fdpic = (l)->fdpic; \
(d)->gotbase = (l)->gotbase; \
(d)->descpool = (l)->descpool; \
(d)->ndesc = (l)->ndesc; \
(d)->usedesc = (l)->usedesc; \
} \
while (0)
#define ARCH_ELFDATA_FINI(d, l) \
do \
{ \
(l)->usedesc = (d)->usedesc; \
} \
while (0)
/* Which relocation table is being walked. A relocation out of DT_JMPREL
* overwrites a word the linker pre-loaded with a lazy binding stub, which is
* not an addend and must not be added to.
*/
#define ARCH_ELFDATA_SET_PLTREL(d, v) (d)->pltrel = (v)
/****************************************************************************
* Public Types
****************************************************************************/
#ifndef __ASSEMBLY__
/* A function descriptor is what an FDPIC function pointer is. Its shape is
* common, so struct fdpic_desc_s from include/nuttx/fdpic.h serves; only a
* pointer to one is kept here, thus the tag is enough.
*/
struct fdpic_desc_s;
struct arch_elfdata_s
{
uint8_t fdpic; /* The object is an FDPIC one */
uintptr_t gotbase; /* DT_PLTGOT: this object's data base */
uint16_t ndesc; /* Capacity, in descriptors */
uint16_t usedesc; /* Next free slot */
/* The pool the descriptors are taken from */
FAR struct fdpic_desc_s *descpool;
uint8_t pltrel; /* Relocation comes from DT_JMPREL, so the word
* it overwrites is a lazy binding stub and not
* an addend
*/
};
typedef struct arch_elfdata_s arch_elfdata_t;
#endif /* __ASSEMBLY__ */
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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