Object-File Sections - 2025.2 English - UG1400

You can create an executable file by concatenating input sections from the object files (.o files). The compiler, by default, creates code across standard and well-defined sections. Each section is named based on its associated meaning and purpose. See the various standard sections of the object file in the following table.

In addition to these sections, you can also create your own custom sections and assign them to memories of your choice.

.text

This section of the object file contains executable program instructions. This section has the x (executable), r (read-only) and i (initialized) flags. You can assign it to an initialized read-only memory (ROM) that is addressable from the processor instruction bus.

.rodata

This section contains read-only data. This section has the r (read-only) and the i (initialized) flags. Like the .text section, you can also assign this section to an initialized, read-only memory addressable from the processor data bus.

.sdata2

This section is similar to the .rodata section. It contains small read-only data of size less than 8 bytes. All data in this section is accessed with reference to the read-only small data anchor. This ensures that all the contents of this section are accessed using a single instruction. You can change the size of the data going into this section with the -G option to the compiler. This section has the r (read-only) and the i (initialized) flags.

.data

This section contains read-write data and has the w (read-write) and the i (initialized) flags. You must map and initialized it to random access memory (RAM). You cannot map it to a ROM.

.sdata

This section contains small read-write data of a size less than 8 bytes. You can change the size of the data going into this section with the -G option. All data in this section is accessed with reference to the read-write small data anchor. This ensures that all contents of the section can be accessed using a single instruction. This section has the w (read-write) and the i (initialized) flags. You must map it to initialized RAM.

.sbss2

This section contains small, read-only uninitialized data of a size less than 8 bytes. You can change the size of the data going into this section with the -G option. This section has the r (read) flag. You can map it to ROM.

.sbss

This section contains small uninitialized data of a size less than 8 bytes. You can change the size of the data going into this section with the -G option. This section has the w (read-write) flag. You must map it to RAM.

.bss

This section contains uninitialized data. This section has the w (read-write) flag. You must map it to RAM.

.heap

This section contains uninitialized data that is used as the global program heap. Dynamic memory allocation routines allocate memory from this section. You must map this section to RAM.

.stack

This section contains uninitialized data that is used as the program stack. You must map this section to RAM. This section is typically laid out right after the .heap section. In some versions of the linker, the .stack and .heap sections can appear merged together into a section named .bss_stack.

.init

This section contains language initialization code and has the same flags as .text. You must map it to initialized ROM.

.fini

This section contains language cleanup code and has the same flags as .text. You must map it to initialized ROM.

.ctors

This section contains a list of functions that must be invoked at program startup and the same flags as .data. You must map it to initialized RAM.

.dtors

This section contains a list of functions that must be invoked at program end, the same flags as .data. You must map it to initialized RAM.

.got2/.got

This section contains pointers to program data, the same flags as .data. You must map it to initialized RAM.

.eh_frame

This section contains frame unwind information for exception handling. It contains the same flags as .rodata. You can map it to initialized ROM.

.tbss

This section holds uninitialized thread-local data that contribute to the program memory image. This section has the same flags as .bss. You must map it to RAM.

.tdata

This section holds initialized thread-local data that contribute to the program memory image. You must map it to initialized RAM.

.gcc_except_table

This section holds language specific data. You must map this section to initialized RAM.

.jcr

This section contains information necessary for registering compiled Java classes. The contents are compiler-specific and used by compiler initialization functions. You must map this section to initialized RAM.

.fixup

This section contains information necessary for doing fixup, such as the fixup page table and the fixup record table. You must map this section to initialized RAM.