ARM Compiler toolchain Using the Linker - ARM Information Center

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3.5 Base Platform linking model Linking models supported by armlink Base Platform enables you to create dynamically linkable images that do not have the memory map enforced by the System V (SysV) or Base Platform Application Binary Interface (BPABI) linking models. It enables you to: • Create images with a memory map described in a scatter file. • Have dynamic relocations so the images can be dynamically linked. The dynamic relocations can also target within the same image. Note The BPABI specification places constraints on the memory model that can be violated using scatter-loading. However, because Base Platform is a superset of BPABI, it is possible to create a BPABI conformant image with Base Platform. To link with the Base Platform model, use the --base_platform command-line option. If you specify this option, the linker acts as if you specified --bpabi, with the following exceptions: • Scatter-loading is available with --scatter, in addition to the following options: — --dll — --force_so_throw, --no_force_so_throw — --pltgot=type is restricted to types none or direct — --ro_base=address — --rosplit — --rw_base=address — --rwpi. • The default value of the --pltgot option is different to that for --bpabi: — for --base_platform, the default is --pltgot=none — for --bpabi the default is --pltgot=direct. • If you do not use a scatter file, the linker can ensure that the Procedure Linkage Table (PLT) section is placed correctly, and contains entries for calls only to imported symbols. If you specify a scatter file, the linker might not be able to find a suitable location to place the PLT. Each load region containing code might require a PLT section to indirect calls from the load region to functions where the address is not known at static link time. The PLT section for a load region LR must be placed in LR and be accessible at all times to code within LR. To ensure calls between relocated load regions ar run-time: — Use the --pltgot=direct option to turn on PLT generation. — Use the --pltgot_opts=crosslr option to add entries in the PLT for calls between RELOC load regions. The linker generates a PLT for each load region so that calls do not have to be extended to reach a distant PLT. Be aware of the following: • The model assumes that shared objects cannot throw a C++ exception. • Symbol versioning must be used to ensure that all the required symbols are available at load time. ARM DUI 0474C Copyright © 2010-2011 ARM. All rights reserved. 3-6 ID080411 Non-Confidential
3.5.1 See also • There are restrictions on the type of scatter files you can use. Linking models supported by armlink Concepts • Base Platform Application Binary Interface (BPABI) linking model on page 3-5 • Concepts common to both BPABI and SysV linking models on page 3-9 • Methods of specifying an image memory map with the linker on page 4-8 • About symbol versioning on page 10-27 • Restrictions on the use of scatter files with the Base Platform model on page 11-2 • Example scatter file for the Base Platform linking model on page 11-5. Reference Linker Reference: • --base_platform on page 2-18 • --dll on page 2-49 • --force_so_throw, --no_force_so_throw on page 2-73 • --pltgot=type on page 2-121 • --pltgot_opts=mode on page 2-122 • --ro_base=address on page 2-135 • --rosplit on page 2-137 • --rw_base=address on page 2-139 • --rwpi on page 2-140 • --scatter=file on page 2-142. ARM DUI 0474C Copyright © 2010-2011 ARM. All rights reserved. 3-7 ID080411 Non-Confidential
Page 1 and 2: ® ARM Copyright © 2010-2011 ARM.
Page 3 and 4: Contents ARM Compiler toolchain Usi
Page 5 and 6: Contents 7.15 Creating a symdefs fi
Page 7 and 8: Chapter 1 Conventions and feedback
Page 9 and 10: Chapter 2 Overview of the linker Th
Page 11 and 12: Concepts • Demand paging on page
Page 13 and 14: 2.3 Linker command-line options lis
Page 15 and 16: • --keep_protected_symbols on pag
Page 17 and 18: • --eager_load_debug, --no_eager_
Page 19 and 20: 2.5 What the linker outputs 2.5.1 S
Page 21 and 22: Chapter 3 Linking models supported
Page 23 and 24: 3.2 Bare-metal linking model 3.2.1
Page 25: Linking models supported by armlink
Page 29 and 30: 3.7 Concepts common to both BPABI a
Page 31 and 32: Image structure and generation •
Page 33 and 34: 4.1.1 See also Image structure and
Page 35 and 36: 4.3 Load view and execution view of
Page 37 and 38: 4.4 Methods of specifying an image
Page 39 and 40: 4.5 Types of simple image 4.5.1 See
Page 47 and 48: 4.10 About specifying an initial en
Page 49 and 50: 4.11.2 Example 4.11.3 See also The
Page 51 and 52: 4.13 Section alignment with the lin
Page 53 and 54: Reference Linker Reference: • --a
Page 55 and 56: 4.16 Overview of veneers 4.16.1 See
Page 57 and 58: 4.18 Veneer types 4.18.1 See also I
Page 59 and 60: 4.20 Reuse of veneers when scatter-
Page 61 and 62: 4.22 About weak references and defi
Page 63 and 64: BL init_foo ;Rest of code END 4.22.
Page 65 and 66: Image structure and generation 4.24
Page 67 and 68: 4.25 Specifying user libraries when
Page 69 and 70: 4.27 Use of the strict family of op
Page 71 and 72: 5.1 Elimination of common debug sec
Page 73 and 74: 5.3 Elimination of unused sections
Page 75 and 76: 5.4 Elimination of unused virtual f
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• --scatter=file on page 2-142. C
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5.6.1 See also Using linker optimiz
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3. Creates the output image. 5.7.3
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5.9 How the linker chooses a compre
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5.11 How compression is applied 5.1
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5.13 Inlining functions with the li
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Reference Assembler Reference: •
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5.16 About reordering of tail calli
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5.18 About merging comment sections
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6.1 Linker options for getting info
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6.3 Example of using the --info lin
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6.4 How to find where a symbol is p
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• Load$$LR$$ load region symbols
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7.2 Accessing linker-defined symbol
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7.4 Image$$ execution region symbol
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7.5.1 See also Accessing and managi
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7.7 Region name values when not sca
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7.9 Importing linker-defined symbol
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7.11 Section-related symbols 7.11.1
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7.13 Input section symbols 7.13.1 S
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7.15 Creating a symdefs file 7.15.1
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7.17 Reading a symdefs file 7.17.1
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7.18.2 See also 0x0000814D T __argv
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7.20 Specifying steering files on t
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7.22 Steering file format 7.22.1 Se
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7.24 Using $Super$$ and $Sub$$ to p
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Using scatter files • Images with
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8.2 When to use scatter-loading 8.2
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• --startup=symbol, --no_startup
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8.4.1 See also Concepts • About s
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8.5.1 See also } SRAM 0x8000 0x8000
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8.7 Specifying stack and heap using
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8.9 Creating root execution regions
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8.9.2 See also Tasks • Using the
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8.11 Placing functions and data at
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Using scatter files RAM 0x200000 (0
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Using scatter files • Using __at
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Developing Software for ARM ® Proc
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} } .ANY1(+RO) ; evenly distributed
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8.14 Examples of using placement al
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Using scatter files 8.15 Example of
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8.16 Examples of using sorting algo
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8.17 Selecting veneer input section
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Compiler Reference: • __attribute
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8.20 Restrictions on placing __at s
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8.21.1 See also Using scatter files
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8.23 Placing a key in flash memory
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8.25 Placement of sections with ove
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8.25.1 See also Using scatter files
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8.27 Example of placing code in a r
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8.29 Example of placing ARM C++ lib
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8.31 Reserving an empty region Usin
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8.32 About creating regions on page
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8.33 Overalignment of execution reg
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8.35 Expression evaluation in scatt
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8.37 Equivalent scatter-loading des
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Using scatter files Example 8-23 Po
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Using scatter files Example 8-25 Po
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Using scatter files • The ER_ZI e
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Using scatter files Example 8-29 Sc
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Chapter 9 GNU ld script support in
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9.2 Typical use cases for using ld
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Reference Linker Reference: • --l
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9.5 Recommendations for using ld sc
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.data : { __data_start = .; *(.data
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9.6.4 See also .got 0 : { *(.got.pl
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9.7.1 See also } .dynamic : { *(.dy
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9.8.1 See also { *(.bss .bss.*) . =
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Chapter 10 BPABI and SysV shared li
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BPABI and SysV shared libraries and
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10.3 Concepts common to all BPABI m
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10.5 Symbol visibility for BPABI mo
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10.6 Automatic import and export fo
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10.8 Symbol versioning for BPABI mo
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10.10 Linker options for SysV model
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10.13 Addressing modes in the SysV
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10.17 Linker options for bare metal
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10.21 Addressing modes in the BPABI
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10.23 About symbol versioning 10.23
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10.25 Example of creating versioned
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10.27 Linker options for enabling i
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Chapter 11 Features of the Base Pla
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Features of the Base Platform linki
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11.2 Example scatter file for the B
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Features of the Base Platform linki
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