ARM Compiler toolchain Using the Linker - ARM Information Center

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5.7 About link-time code generation 5.7.1 Considerations when using LTCG 5.7.2 Example Using linker optimizations Link-time code generation (LTCG) enables cross source-file optimization by delaying code generation until the link stage. This can significantly reduce code size. To enable LTCG, compile your source with -c --ltcg to create objects in an intermediate format. You must then link these object files with --ltcg to instruct the linker to perform code generation. Both armcc and armlink have a --ltcg command-line option to enable LTCG. Note You can also use LTCG with Profiler-guided optimizations. Be aware of the following when using LTCG: • If no input objects are compiled with --ltcg, the final object is the same as that produced without LTCG. • Debug information is not preserved in any object files compiled with --ltcg. However, debug information is still preserved for any object files that are not compiled with --ltcg. • You cannot use specific object file names in scatter files because LTCG causes a temporary object file to be created and used for linking. If you are using a scatter file, then you must match files using the wildcard *. Otherwise no match is made on the temporary file. • If there is more than one entry point in the input object files provided to the linker, the linker clears all entry points. Therefore, you must specify an entry point on the linker command-line with: --entry=symbol Any input section containing an entry point is not removed. For example, where an object is built without --ltcg. Note The linker option --entry=object(symbol) is not supported when using LTCG. The following example shows a typical use of LTCG: 1. Create ELF object files one.o and two.o with --ltcg: armcc -c --ltcg one.c -o one.o armcc -c --ltcg two.c -o two.o The compiler generates intermediate code into the object files. 2. Link them using the command: armlink --ltcg one.o two.o -o ltcg_image.axf The linker: 1. Combines all the immediate code together, losing the link to original object file names. 2. Performs code generation for the intermediate code. ARM DUI 0474C Copyright © 2010-2011 ARM. All rights reserved. 5-11 ID080411 Non-Confidential
3. Creates the output image. 5.7.3 About the intermediate object files generated by link-time code generation 5.7.4 See also Using linker optimizations An intermediate ELF object file generated by link-time code generation (LTCG) includes a section called .il, This section is marked with the flags SHF_EXECINSTR and SHF_ALLOC. Using the intermediate object file one.o from the example, you can use the fromelf command to view these sections, for example: fromelf --text -v one.o ... ==================================== ** Section #1 Name : .il Type : SHT_PROGBITS (0x00000001) Flags : SHF_ALLOC + SHF_EXECINSTR (0x00000006) ... Link : SHN_UNDEF ... ==================================== ** Section #3 Name : .rel.il Type : SHT_REL (0x00000009) Flags : None (0x00000000) ... Link : Section 2 (.symtab) Info : Section 1 (.il) ... ==================================== ... Concepts Using the Compiler: • About Profiler-guided optimization on page 5-3 • Profiler-guided optimizations with link-time code generation on page 5-4. Reference Linker Reference: • --entry=location on page 2-58 • --ltcg on page 2-106. Compiler Reference: • -c on page 3-31 • --ltcg on page 3-141. Using the fromelf Image Converter: • --text on page 4-73. ARM DUI 0474C Copyright © 2010-2011 ARM. All rights reserved. 5-12 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
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Chapter 3 Linking models supported
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3.2 Bare-metal linking model 3.2.1
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Linking models supported by armlink
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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
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
Page 77 and 78: • --scatter=file on page 2-142. C
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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
Page 105 and 106: 7.4 Image$$ execution region symbol
Page 107 and 108: 7.5.1 See also Accessing and managi
Page 109 and 110: 7.7 Region name values when not sca
Page 111 and 112: 7.9 Importing linker-defined symbol
Page 113 and 114: 7.11 Section-related symbols 7.11.1
Page 115 and 116: 7.13 Input section symbols 7.13.1 S
Page 117 and 118: 7.15 Creating a symdefs file 7.15.1
Page 119 and 120: 7.17 Reading a symdefs file 7.17.1
Page 121 and 122: 7.18.2 See also 0x0000814D T __argv
Page 123 and 124: 7.20 Specifying steering files on t
Page 125 and 126: 7.22 Steering file format 7.22.1 Se
Page 127 and 128: 7.24 Using $Super$$ and $Sub$$ to p
Page 129 and 130: 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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Change Topics affected Revisions fo
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