What is "isra" in the kernel thread dump

Question

Linux kernel call stack dump often includes function names that ends with ".isra.NNN" where NNN is some numbers. For example, see here and here.

What does that mean, what does the number signify?

Answer 1

isra is the suffix added to the function name when gcc option -fipa-sra compiler optimization being carried out.

From gcc manual:

-fipa-sra

Perform interprocedural scalar replacement of aggregates, removal of unused parameters and replacement of parameters passed by reference by parameters passed by value.

Enabled at levels -O2, -O3 and -Os.

All functions that are optimized under this option have isra appended to their names. I digged into gcc code and found out the function that was appending the string.

tree
clone_function_name (tree decl, const char *suffix)
{
  tree name = DECL_ASSEMBLER_NAME (decl);
  size_t len = IDENTIFIER_LENGTH (name);
  char *tmp_name, *prefix;

  prefix = XALLOCAVEC (char, len + strlen (suffix) + 2);
  memcpy (prefix, IDENTIFIER_POINTER (name), len);
  strcpy (prefix + len + 1, suffix);
#ifndef NO_DOT_IN_LABEL
  prefix[len] = '.';
#elif !defined NO_DOLLAR_IN_LABEL
  prefix[len] = '$';
#else
  prefix[len] = '_';
#endif
  ASM_FORMAT_PRIVATE_NAME (tmp_name, prefix, clone_fn_id_num++);
  return get_identifier (tmp_name);
}

Here, argument 2, const char *suffix, is "isra" and notice at the bottom of the function macro ASM_FORMAT_PRIVATE_NAME which takes clone_fn_id_num++ as its 3rd argument. This is the arbitrary number found after "isra". This going by its name is the count of functions that are cloned under this compiler option (or may be a global counter that keeps track of all cloned functions).

If you want to understand more, search for modify_function in file gcc/tree-sra.c which in turn calls cgraph_function_versioning() which passes "isra" as its last argument.