[Bug ada/70017] New: Ada: c52103x test failure on s390x

["vogt at linux dot vnet.ibm.com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70017

            Bug ID: 70017
           Summary: Ada: c52103x test failure on s390x
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ada
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vogt at linux dot vnet.ibm.com
                CC: ebotcazou at gcc dot gnu.org, krebbel at gcc dot gnu.org
  Target Milestone: ---
              Host: s390x
            Target: s390x

My knowledge of Ada is practically zero, but I'm debugging a few Ada test
failures on s390x (gcc-4.7 or earlier).

-- snip --
,.,. C52103X ACATS 2.5 16-02-29 16:03:21
---- C52103X CHECK THAT IN ARRAY ASSIGNMENTS AND IN SLICE ASSIGNMENTS,
                THE LENGTHS MUST MATCH; ALSO CHECK WHETHER
                CONSTRAINT_ERROR OR STORAGE_ERROR ARE RAISED FOR LARGE
                ARRAYS.
   - C52103X NO CONSTRAINT_ERROR FOR TYPE WITH 'LENGTH = INTEGER'LAST + 
                3.
raised STORAGE_ERROR : System.Stack_Checking.Operations.Stack_Check: stack
over\
flow detected
FAIL:   c52103x 
-- snip --

This happens here:

-- snip --
               TYPE  TA42  IS  ARRAY( 
                    INTEGER RANGE IDENT_INT(-2)..IDENT_INT(INTEGER'LAST) 
                                    )  OF BOOLEAN ;
...
OBJ_DCL:       DECLARE   -- THIS BLOCK DECLARES TWO BOOLEAN ARRAYS THAT 
                         -- HAVE INTEGER'LAST + 3 COMPONENTS; 
                         -- STORAGE_ERROR MAY BE RAISED. 
                    ARR41  :  TA41 ; 
                    ARR42  :  TA42 ; 
-- snip --

This is a reduced test (that fails with ulimit -s 131072):
-- snip --
procedure c52103x is 
begin 
        declare 
                type T is array(integer range -2..10000000) of boolean; 
        begin 
                declare 
                        A : T; 
                begin 
                        null; 
                end; 
        end; 
end; 
-- snip --

As far as I understand this code, it assumes that only the first few memory
pages of the array are allocated in the stack initially and the rest is
allocated when actually accessed.  However, on s390x first a snippet of three
pages is allocated and checked, followed immediately by the rest of the array
plus another check that fails because the stack is too small for that:

-- snip --
_ada_c52103x: 
        stmg    %r11,%r15,88(%r15) 
        larl    %r13,.L4 
        aghi    %r15,-168 
        lgr     %r11,%r15 
        lgr     %r1,%r15 
        aghi    %r1,-12280  # <-- first three pages
        lgr     %r2,%r1 
        brasl   %r14,_gnat_stack_check # <-- OK
        lgr     %r1,%r15 
        lgr     %r12,%r1 
        lg      %r1,.L5-.L4(%r13) 
        agr     %r1,%r15    # <-- rest of array
        lgr     %r2,%r1 
        brasl   %r14,_gnat_stack_check # <-- FAIL
        ...

        .section        .rodata 
        .align  8 
.L4: 
.L6: 
        .quad   -10000008 
.L5: 
        .quad   -10012288 
-- snip --

(Stack on s390x grows down.)

I've no idea whether this is the intended behaviour (i.e. the test case has a
bug) or not, and if not whether I should look for the bug in the s390x backend
or somewhere else.