Arm Compiler armlink User Guide : 6.1 About mapping symbols

6.1 About mapping symbols

Mapping symbols are generated by the compiler and assembler to identify various inline transitions.

For Arm^®v7‑A, inline transitions can be between:

Code and data at literal pool boundaries.
Arm code and Thumb code, such as Arm and Thumb interworking veneers.

For Armv8‑A, inline transitions can be between:

Code and data at literal pool boundaries.
A32 code and T32 code, such as A32 and T32 interworking veneers.

For Armv6‑M, Armv7‑M, and Armv8‑M, inline transitions can be between code and data at literal pool boundaries.

The mapping symbols available for each architecture are:

Symbol	Description	Architecture
`$a`	Start of a sequence of Arm/A32 instructions.	All
`$t`	Start of a sequence of Thumb/T32 instructions.	All
`$t.x`	Start of a sequence of ThumbEE instructions.	Armv7‑A
`$d`	Start of a sequence of data items, such as a literal pool.	All
`$x`	Start of A64 code.	Armv8‑A

armlink generates the $d.realdata mapping symbol to communicate to fromelf that the data is from a non-executable section. Therefore, the code and data sizes output by fromelf -z are the same as the output from armlink --info sizes, for example:

      Code (inc. data)   RO Data
         x          y          z

In this example, the y is marked with $d, and RO Data is marked with $d.realdata.

Note:

Symbols beginning with the characters $v are mapping symbols related to VFP and might be output when building for a target with VFP. Avoid using symbols beginning with $v in your source code.

Be aware that modifying an executable image with the fromelf --elf --strip=localsymbols command removes all mapping symbols from the image.

Related references

11.76 --list_mapping_symbols, --no_list_mapping_symbols

11.135 --strict_symbols, --no_strict_symbols

Related information

Symbol naming rules

--strip=option[,option,…] fromelf option

--text fromelf option

ELF for the Arm Architecture

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