Using the C and C++ libraries

Use of the Arm^® C and C++ libraries

You can use the Arm C and C++ libraries with the SysV linking model by statically linking the main executable with them. You must appropriately retarget the library for the platform.

Integration with a dynamic loader

• The Arm C and C++ libraries with the SysV linking model by statically linking the main C library executes pre-initialization (.prenit_array) and initialization functions (.init_array) that are present only in the main executable. The library is not aware of initialization functions in loaded shared objects.

  To enable running initialization routines in the whole program, you can link the main executable with armlink --no_preinit --no_cppinit and provide custom implementation of __arm_preinit_() and __cpp_initialize__aeabi_(). The overridden functions must integrate with a platform dynamic loader to execute all initialization functions.

  The dynamic loader can use dynamic entries DT_PREINIT_ARRAY, DT_INIT_ARRAY, DT_INIT to obtain initialization functions in the executable and each shared object.

• The Arm C++ library by default supports exceptions only in the main executable. To allow exceptions in loaded shared objects, you can provide implementation of __arm_find_exidx_section() (in AArch32 state) and __arm_find_eh_frame_hdr_section() (in AArch64 state):

  /* AArch32 hook */
  int __arm_find_exidx_section(uintptr_t target_addr, uintptr_t *base, size_t *length);
  
  /* AArch64 hook */
  int __arm_find_eh_frame_hdr_section(uintptr_t target_addr, uintptr_t *base, size_t *length);

  The functions receive an address of code that needs to be unwound and must find an exception-index section associated with this location. Parameter target_addr specifies an address of code that needs to be unwound. Parameters base and length point to values that must be set by the function to the address and size of the found exception-index section. Return value 0 indicates success, non-zero value indicates a failure. The dynamic loader can use segments PT_ARM_EXIDX (in AArch32 state) and PT_GNU_EH_FRAME (in AArch64 state) to locate the exception-index sections.

Use of the platform C and C++ libraries

It is possible to use system libraries that come with the target platform.

The code of the program must be compiled with the armclang -nostdlib and -nostdlibinc command-line options to indicate to the compiler to not use the Arm C and C++ libraries.

Executable and shared objects must be linked with the armlink --no_scanlib command-line option.