http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59039
--- Comment #18 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> I couldn't find anything in GCC manual.
There are a few documented hooks, but this looks quite light indeed, so the
sources are probably the best references, i.e. builtins.c and except.c:
/* __builtin_longjmp is passed a pointer to an array of five words (not
all will be used on all machines). It operates similarly to the C
library function of the same name, but is more efficient. Much of
the code below is copied from the handling of non-local gotos. */
static void
expand_builtin_longjmp (rtx buf_addr, rtx value)
{
rtx fp, lab, stack, insn, last;
enum machine_mode sa_mode = STACK_SAVEAREA_MODE (SAVE_NONLOCAL);
void
init_eh (void)
{
[...]
#ifdef DONT_USE_BUILTIN_SETJMP
#ifdef JMP_BUF_SIZE
tmp = size_int (JMP_BUF_SIZE - 1);
#else
/* Should be large enough for most systems, if it is not,
JMP_BUF_SIZE should be defined with the proper value. It will
also tend to be larger than necessary for most systems, a more
optimal port will define JMP_BUF_SIZE. */
tmp = size_int (FIRST_PSEUDO_REGISTER + 2 - 1);
#endif
#else
/* builtin_setjmp takes a pointer to 5 words. */
tmp = size_int (5 * BITS_PER_WORD / POINTER_SIZE - 1);
#endif
tmp = build_index_type (tmp);
tmp = build_array_type (ptr_type_node, tmp);
f_jbuf = build_decl (BUILTINS_LOCATION,
FIELD_DECL, get_identifier ("__jbuf"), tmp);
#ifdef DONT_USE_BUILTIN_SETJMP
/* We don't know what the alignment requirements of the
runtime's jmp_buf has. Overestimate. */
DECL_ALIGN (f_jbuf) = BIGGEST_ALIGNMENT;
DECL_USER_ALIGN (f_jbuf) = 1;
#endif
