ARM Compiler toolchain Using the Linker - ARM Information Center

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5.2 Elimination of common groups or sections 5.2.1 See also The ARM compiler generates complete objects for linking. Therefore: Using linker optimizations • If there are inline functions in C and C++ sources, each object contains the out-of-line copies of the inline functions that the object requires. • If templates are used in C++ sources, each object contains the template functions that the object requires. When these functions are declared in a common header file, the functions might be defined many times in separate objects that are subsequently linked together. To eliminate duplicates, the compiler compiles these functions into separate instances of common code sections or groups. It is possible that the separate instances of common code sections, or groups, are not identical. Some of the copies, for example, might be found in a library that has been built with different, but compatible, build options, different optimization, or debug options. If the copies are not identical, armlink retains the best available variant of each common code section, or group, based on the attributes of the input objects. armlink discards the rest. If the copies are identical, armlink retains the first section or group located. You control this optimization with the following linker options: • Use the --bestdebug option to use the largest common data (COMDAT) group (likely to give the best debug view). • Use the --no_bestdebug option to use the smallest COMDAT group (likely to give the smallest code size). This is the default. Because --no_bestdebug is the default, the final image is the same regardless of whether you generate debug tables during compilation with --debug. Concepts • Input sections, output sections, regions, and Program Segments on page 4-5. • Elimination of common debug sections on page 5-2 • Elimination of unused sections on page 5-4 • Elimination of unused virtual functions on page 5-6. Using the Compiler: • Inline functions on page 6-29. Reference Linker Reference: • --bestdebug, --no_bestdebug on page 2-21. Compiler Reference: • --debug, --no_debug on page 3-55. ARM DUI 0474C Copyright © 2010-2011 ARM. All rights reserved. 5-3 ID080411 Non-Confidential
5.3 Elimination of unused sections 5.3.1 See also Using linker optimizations Unused section elimination is the most significant optimization on image size that is performed by the linker. It removes unreachable code and data from the final image. Unused section elimination is suppressed in cases that might result in the removal of all sections. To control this optimization use the --remove, --no_remove, --first, --last, and --keep linker options. Unused section elimination requires an entry point. Therefore, if there is no entry point specified for an image, use the --entry linker option to specify an entry point and permit unused section elimination to work, if it is enabled. Note By default, unused section elimination is disabled if you are building DLLs with --dll, or shared libraries with --shared. Therefore, you must explicitly include --remove to re-enable unused section elimination. Use the --info unused linker option to instruct the linker to generate a list of the unused sections that it eliminates. An input section is retained in the final image under the following conditions: • if it contains an entry point • if it is referred to, directly or indirectly, by a non-weak reference from an input section containing an entry point • if it is specified as the first or last input section by the --first or --last option (or a scatter-loading equivalent) • if it is marked as unremovable by the --keep option. Note Compilers usually collect functions and data together and emit one section for each category. The linker can only eliminate a section if it is entirely unused. You can mark a function or variable in source code with the __attribute__((used)) attribute. This causes armcc to generate the symbol __tagsym$$used for each of the functions and variables, and ensures that the function or variable is not removed by the linker. You can also use the --split_sections compiler command-line option to instruct the compiler to generate one ELF section for each function in the source file. Concepts • Input sections, output sections, regions, and Program Segments on page 4-5 • About weak references and definitions on page 4-32 • Elimination of common debug sections on page 5-2 • Elimination of common groups or sections on page 5-3 • Elimination of unused virtual functions on page 5-6. ARM DUI 0474C Copyright © 2010-2011 ARM. All rights reserved. 5-4 ID080411 Non-Confidential
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® ARM Copyright © 2010-2011 ARM.
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Contents ARM Compiler toolchain Usi
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Contents 7.15 Creating a symdefs fi
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Chapter 1 Conventions and feedback
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Chapter 2 Overview of the linker Th
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Concepts • Demand paging on page
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2.3 Linker command-line options lis
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• --keep_protected_symbols on pag
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• --eager_load_debug, --no_eager_
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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 and 26: Linking models supported by armlink
Page 27 and 28: 3.5.1 See also • There are restri
Page 29 and 30: 3.7 Concepts common to both BPABI a
Page 31 and 32: Image structure and generation •
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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
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Page 77 and 78: • --scatter=file on page 2-142. C
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Page 81 and 82: 3. Creates the output image. 5.7.3
Page 83 and 84: 5.9 How the linker chooses a compre
Page 85 and 86: 5.11 How compression is applied 5.1
Page 87 and 88: 5.13 Inlining functions with the li
Page 89 and 90: Reference Assembler Reference: •
Page 91 and 92: 5.16 About reordering of tail calli
Page 93 and 94: 5.18 About merging comment sections
Page 95 and 96: 6.1 Linker options for getting info
Page 97 and 98: 6.3 Example of using the --info lin
Page 99 and 100: 6.4 How to find where a symbol is p
Page 101 and 102: • Load$$LR$$ load region symbols
Page 103 and 104: 7.2 Accessing linker-defined symbol
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Page 107 and 108: 7.5.1 See also Accessing and managi
Page 109 and 110: 7.7 Region name values when not sca
Page 111 and 112: 7.9 Importing linker-defined symbol
Page 113 and 114: 7.11 Section-related symbols 7.11.1
Page 115 and 116: 7.13 Input section symbols 7.13.1 S
Page 117 and 118: 7.15 Creating a symdefs file 7.15.1
Page 119 and 120: 7.17 Reading a symdefs file 7.17.1
Page 121 and 122: 7.18.2 See also 0x0000814D T __argv
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7.20 Specifying steering files on t
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7.22 Steering file format 7.22.1 Se
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7.24 Using $Super$$ 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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