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Preface Arm Compiler Tools Overview armclang Reference armlink Reference armlink Command-line Options --any_contingency --any_placement=algorithm --any_sort_order=order --api, --no_api --autoat, --no_autoat --bare_metal_pie --base_platform --be8 --be32 --bestdebug, --no_bestdebug --blx_arm_thumb, --no_blx_arm_thumb --blx_thumb_arm, --no_blx_thumb_arm --bpabi --branchnop, --no_branchnop --callgraph, --no_callgraph --callgraph_file=filename --callgraph_output=fmt --callgraph_subset=symbol[,symbol,...] --cgfile=type --cgsymbol=type --cgundefined=type --comment_section, --no_comment_section --cppinit, --no_cppinit --cpu=list (armlink) --cpu=name (armlink) --crosser_veneershare, --no_crosser_veneershare --datacompressor=opt --debug, --no_debug --diag_error=tag[,tag,…] (armlink) --diag_remark=tag[,tag,…] (armlink) --diag_style={arm|ide|gnu} (armlink) --diag_suppress=tag[,tag,…] (armlink) --diag_warning=tag[,tag,…] (armlink) --dll --dynamic_linker=name --eager_load_debug, --no_eager_load_debug --eh_frame_hdr --edit=file_list --emit_debug_overlay_relocs --emit_debug_overlay_section --emit_non_debug_relocs --emit_relocs --entry=location --errors=filename --exceptions, --no_exceptions --export_all, --no_export_all --export_dynamic, --no_export_dynamic --filtercomment, --no_filtercomment --fini=symbol --first=section_id --force_explicit_attr --force_so_throw, --no_force_so_throw --fpic --fpu=list (armlink) --fpu=name (armlink) --got=type --gnu_linker_defined_syms --help (armlink) --import_cmse_lib_in=filename --import_cmse_lib_out=filename --import_unresolved, --no_import_unresolved --info=topic[,topic,…] (armlink) --info_lib_prefix=opt --init=symbol --inline, --no_inline --inline_type=type --inlineveneer, --no_inlineveneer input-file-list (armlink) --keep=section_id (armlink) --keep_intermediate --largeregions, --no_largeregions --last=section_id --legacyalign, --no_legacyalign --libpath=pathlist --library=name --library_security=protection --library_type=lib --list=filename --list_mapping_symbols, --no_list_mapping_symbols --load_addr_map_info, --no_load_addr_map_info --locals, --no_locals --lto, --no_lto --lto_keep_all_symbols, --no_lto_keep_all_symbols --lto_intermediate_filename --lto_level --lto_relocation_model --mangled, --unmangled --map, --no_map --max_er_extension=size --max_veneer_passes=value --max_visibility=type --merge, --no_merge --merge_litpools, --no_merge_litpools --muldefweak, --no_muldefweak -o filename, --output=filename (armlink) --output_float_abi=option --overlay_veneers --override_visibility -Omax (armlink) --pad=num --paged --pagesize=pagesize --partial --pie --piveneer, --no_piveneer --pixolib --pltgot=type --pltgot_opts=mode --predefine="string" --preinit, --no_preinit --privacy (armlink) --ref_cpp_init, --no_ref_cpp_init --ref_pre_init, --no_ref_pre_init --reloc --remarks --remove, --no_remove --ro_base=address --ropi --rosplit --rw_base=address --rwpi --scanlib, --no_scanlib --scatter=filename --section_index_display=type --shared --show_cmdline (armlink) --show_full_path --show_parent_lib --show_sec_idx --soname=name --sort=algorithm --split --startup=symbol, --no_startup --stdlib --strict --strict_flags, --no_strict_flags --strict_ph, --no_strict_ph --strict_preserve8_require8 --strict_relocations, --no_strict_relocations --strict_symbols, --no_strict_symbols --strict_visibility, --no_strict_visibility --symbols, --no_symbols --symdefs=filename --symver_script=filename --symver_soname --sysv --tailreorder, --no_tailreorder --tiebreaker=option --unaligned_access, --no_unaligned_access --undefined=symbol --undefined_and_export=symbol --unresolved=symbol --use_definition_visibility --userlibpath=pathlist --veneerinject, --no_veneerinject --veneer_inject_type=type --veneer_pool_size=size --veneershare, --no_veneershare --verbose --version_number (armlink) --via=filename (armlink) --vsn (armlink) --xo_base=address --xref, --no_xref --xrefdbg, --no_xrefdbg --xref{from|to}=object(section) --zi_base=address Linking Models Supported by armlink Overview of linking models Bare-metal linking model overview Partial linking model overview Base Platform Application Binary Interface (BPABI) Base Platform linking model overview SysV linking model overview Concepts common to both BPABI and SysV linking mod Image Structure and Generation The structure of an Arm ELF image Views of the image at each link stage Input sections, output sections, regions, and prog Load view and execution view of an image Methods of specifying an image memory map with the Image entry points Restrictions on image structure Simple images Types of simple image Type 1 image structure, one load region and contig Type 2 image structure, one load region and non-co Type 3 image structure, multiple load regions and Section placement with the linker Default section placement Section placement with the FIRST and LAST attribut Section alignment with the linker Linker support for creating demand-paged files Linker reordering of execution regions containing Linker-generated veneers What is a veneer? Veneer sharing Veneer types Generation of position independent to absolute ven Reuse of veneers when scatter-loading Generation of secure gateway veneers Command-line options used to control the generatio Weak references and definitions How the linker performs library searching, selecti How the linker searches for the Arm standard libra Specifying user libraries when linking How the linker resolves references The strict family of linker options Linker Optimization Features Elimination of common section groups Elimination of unused sections Optimization with RW data compression How the linker chooses a compressor Options available to override the compression algo How compression is applied Considerations when working with RW data compressi Function inlining with the linker Factors that influence function inlining About branches that optimize to a NOP Linker reordering of tail calling sections Restrictions on reordering of tail calling section Linker merging of comment sections Merging identical constants Accessing and Managing Symbols with armlink About mapping symbols Linker-defined symbols Region-related symbols Types of region-related symbols Image$$ execution region symbols Load$$ execution region symbols Load$$LR$$ load region symbols Region name values when not scatter-loading Linker defined symbols and scatter files Methods of importing linker-defined symbols in C a Methods of importing linker-defined symbols in Arm Section-related symbols Types of section-related symbols Image symbols Input section symbols Access symbols in another image Creating a symdefs file Outputting a subset of the global symbols Reading a symdefs file Symdefs file format Edit the symbol tables with a steering file Specifying steering files on the linker command-li Steering file command summary Steering file format Hide and rename global symbols with a steering fil Use of $Super$$ and $Sub$$ to patch symbol definit Scatter-loading Features The scatter-loading mechanism Overview of scatter-loading When to use scatter-loading Linker-defined symbols that are not defined when s Placing the stack and heap with a scatter file Scatter-loading command-line options Scatter-loading images with a simple memory map Scatter-loading images with a complex memory map Root region and the initial entry point Effect of the ABSOLUTE attribute on a root region Effect of the FIXED attribute on a root region Methods of placing functions and data at specific Placing functions and data in a named section Placing __at sections at a specific address Restrictions on placing __at sections Automatically placing __at sections Manually placing __at sections Placing a key in flash memory with an __at section Example of how to explicitly place a named section Placement of unassigned sections Default rules for placing unassigned sections Command-line options for controlling the placement Prioritizing the placement of unassigned sections Specify the maximum region size permitted for plac Examples of using placement algorithms for .ANY se Example of next_fit algorithm showing behavior of Examples of using sorting algorithms for .ANY sect Behavior when .ANY sections overflow because of li Placing veneers with a scatter file Placement of CMSE veneer sections for a Secure ima Reserving an empty block of memory Characteristics of a reserved empty block of memor Example of reserving an empty block of memory Placement of Arm C and C++ library code Placing code in a root region Placing Arm C library code Placing Arm C++ library code Aligning regions to page boundaries Aligning execution regions and input sections Preprocessing a scatter file Default behavior for armclang -E in a scatter file Using other preprocessors in a scatter file Example of using expression evaluation in a scatte Equivalent scatter-loading descriptions for simple Command-line options for creating simple images Type 1 image, one load region and contiguous execu Type 2 image, one load region and non-contiguous e Type 3 image, multiple load regions and non-contig How the linker resolves multiple matches when proc How the linker resolves path names when processing Scatter file to ELF mapping Scatter File Syntax BNF notation used in scatter-loading description s Syntax of a scatter file Load region descriptions Components of a load region description Syntax of a load region description Load region attributes Inheritance rules for load region address attribut Inheritance rules for the RELOC address attribute Considerations when using a relative address +offs Execution region descriptions Components of an execution region description Syntax of an execution region description Execution region attributes Inheritance rules for execution region address att Considerations when using a relative address +offs Input section descriptions Components of an input section description Syntax of an input section description Examples of module and input section specification Expression evaluation in scatter files Expression usage in scatter files Expression rules in scatter files Execution address built-in functions for use in sc ScatterAssert function and load address related fu Symbol related function in a scatter file AlignExpr(expr, align) function GetPageSize() function SizeOfHeaders() function Example of aligning a base address in execution sp Scatter files containing relative base address loa BPABI and SysV Shared Libraries and Executables About the Base Platform Application Binary Interfa Platforms supported by the BPABI Features common to all BPABI models About importing and exporting symbols for BPABI mo Symbol visibility for BPABI models Automatic import and export for BPABI models Manual import and export for BPABI models Symbol versioning for BPABI models RW compression for BPABI models SysV linking model SysV standard memory model Using the C and C++ libraries Using a dynamic Linker Automatic dynamic symbol table rules in the SysV l Symbol definitions defined for SysV compatibility Addressing modes in the SysV linking model Thread local storage in the SysV linking model Linker command-line options for the SysV linking m Bare metal and DLL-like memory models BPABI standard memory model Customization of the BPABI standard memory model Linker command-line options for bare metal and DLL Mandatory symbol versioning in the BPABI DLL-like Automatic dynamic symbol table rules in the BPABI Addressing modes in the BPABI DLL-like model C++ initialization in the BPABI DLL-like model Symbol versioning Overview of symbol versioning Embedded symbols The symbol versioning script file Example of creating versioned symbols Linker options for enabling implicit symbol versio Features of the Base Platform Linking Model Restrictions on the use of scatter files with the Scatter files for the Base Platform linking model Placement of PLT sequences with the Base Platform Linker Steering File Command Reference EXPORT steering file command HIDE steering file command IMPORT steering file command RENAME steering file command REQUIRE steering file command RESOLVE steering file command SHOW steering file command fromelf Reference armar Reference armasm Legacy Assembler Reference Appendixes

Behavior when .ANY sections overflow because of linker-generated content

C6.4.8 Behavior when .ANY sections overflow because of linker-generated content

Because linker-generated content might cause .ANY sections to overflow, a contingency algorithm is included in the linker.

The linker does not know the address of a section until it is assigned to a region. Therefore, when filling .ANY regions, the linker cannot calculate the contingency space and cannot determine if calling functions require veneers. The linker provides a contingency algorithm that gives a worst-case estimate for padding and an extra two percent for veneers. To enable this algorithm, use the --any_contingency command-line option.

The following diagram represents an example image layout during .ANY placement:

Figure C6-4 .ANY contingency
.ANY contingency

The downward arrows for prospective padding show that the prospective padding continues to grow as more sections are added to the .ANY selector.

Prospective padding is dealt with before the two percent veneer contingency.

When the prospective padding is cleared, the priority is set to zero. When the two percent is cleared, the priority is decremented again.

You can also use the ANY_SIZE keyword on an execution region to specify the maximum amount of space in the region to set aside for .ANY section assignments.

You can use the armlink command-line option --info=any to get extra information on where the linker has placed sections. This information can be useful when trying to debug problems.

Note:

When there is only one .ANY selector, it might not behave identically to *. The algorithms that are used to determine the size of the section and place data still run with .ANY and they try to estimate the impact of changes that might affect the size of sections.These algorithms do not run if * is used instead. When it is appropriate to use one or the other of .ANY or *, then you must not use a single .ANY selector that applies to a kind of data, such as RO, RW, or ZI. For example, .ANY (+RO).

You might see error L6407E generated, for example:

Error: L6407E: Sections of aggregate size 0x128 bytes could not fit into .ANY selector(s).

However, increasing the section size by 0x128 bytes does not necessarily lead to a successful link. The failure to link is because of the extra data, such as region table entries, that might end up in the region after adding more sections.

Example

  1. Create the following foo.c program:
    #include "stdio.h"
    
    int array[10] __attribute__ ((section ("ARRAY")));
    
    struct S {
        char A[8];
        char B[4];
    };
    struct S s;
    
    struct S* get()
    {
        return &s;
    }
    
    int sqr(int n1);
    int gSquared __attribute__((section(".ARM.__at_0x5000")));  // Place at 0x5000
    
    int sqr(int n1)
    {
        return n1*n1;
    }
    
    int main(void) {
        int i;
        for (i=0; i<10; i++) {
            array[i]=i*i;
            printf("%d\n", array[i]);
        }
        gSquared=sqr(i);
        printf("%d squared is: %d\n", i, gSquared);
    
        return sizeof(array);
    }
    
  2. Create the following scatter.scat file:
    LOAD_REGION 0x0 0x3000
    {
       ER_1 0x0 0x1000
       {
          .ANY
       }
       ER_2 (ImageLimit(ER_1)) 0x1500
       {
          .ANY
       }
       ER_3 (ImageLimit(ER_2)) 0x500
       {
          .ANY
       }
       ER_4 (ImageLimit(ER_3)) 0x1000
       {
           *(+RW,+ZI)
       }
       ARM_LIB_STACK 0x800000 EMPTY -0x10000
       {
       }
       ARM_LIB_HEAP  +0 EMPTY 0x10000
       {
       }
    }
    
  3. Compile and link the program as follows:
    armclang -c --target=arm-arm-none-eabi -mcpu=cortex-m4 -o foo.o foo.c
    armlink --cpu=cortex-m4 --any_contingency --scatter=scatter.scat --info=any -o foo.axf foo.o

The following shows an example of the information generated:

==============================================================================


Sorting unassigned sections by descending size for .ANY placement.
Using Worst Fit .ANY placement algorithm.
.ANY contingency enabled.

Exec Region    Event                         Idx          Size        Section Name                  Object
ER_2           Assignment: Worst fit         144          0x0000041a  .text                         c_wu.l(_printf_fp_dec.o)
ER_2           Assignment: Worst fit         261          0x00000338  CL$$btod_div_common           c_wu.l(btod.o)
ER_1           Assignment: Worst fit         146          0x000002fc  .text                         c_wu.l(_printf_fp_hex.o)
ER_2           Assignment: Worst fit         260          0x00000244  CL$$btod_mult_common          c_wu.l(btod.o)
...
ER_1           Assignment: Worst fit         3            0x00000090  .text                         foo.o
...
ER_3           Assignment: Worst fit         100          0x0000000a  .ARM.Collect$$_printf_percent$$00000007  c_wu.l(_printf_ll.o)
ER_3           Info: .ANY limit reached      -            -           -                             -
ER_1           Assignment: Highest priority  423          0x0000000a  .text                         c_wu.l(defsig_exit.o)
...
.ANY contingency summary
Exec Region    Contingency     Type
ER_1           161             Auto
ER_2           180             Auto
ER_3           73              Auto

==============================================================================


Sorting unassigned sections by descending size for .ANY placement.
Using Worst Fit .ANY placement algorithm.
.ANY contingency enabled.

Exec Region    Event                         Idx          Size        Section Name                  Object
ER_2           Info: .ANY limit reached      -            -           -                             -
ER_1           Info: .ANY limit reached      -            -           -                             -
ER_3           Info: .ANY limit reached      -            -           -                             -
ER_2           Assignment: Worst fit         533          0x00000034  !!!scatter                    c_wu.l(__scatter.o)
ER_2           Assignment: Worst fit         535          0x0000001c  !!handler_zi                  c_wu.l(__scatter_zi.o)
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