From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=unavailable autolearn_force=no version=3.4.4 Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail From: "Alejandro R. Mosteo" Newsgroups: comp.lang.ada Subject: Re: Error: allocation from empty storage pool Date: Thu, 12 Jul 2018 14:14:12 +0200 Organization: A noiseless patient Spider Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Thu, 12 Jul 2018 12:14:12 -0000 (UTC) Injection-Info: reader02.eternal-september.org; posting-host="6cef34ecda19d976dcb53c5929155828"; logging-data="28254"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+oabYUQVHV+4CBVg5kYOR8" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 Cancel-Lock: sha1:JNmPQYYiezu/fTYrBSbVTtI61g0= In-Reply-To: Content-Language: en-US Xref: reader02.eternal-september.org comp.lang.ada:53777 Date: 2018-07-12T14:14:12+02:00 List-Id: On 12/07/2018 13:41, Simon Wright wrote: > "Alejandro R. Mosteo" writes: > >> In a library I'm trying to have all allocations done from >> user-specified storage pools. There is no restriction on using the >> heap, as long as it comes from a user pool (that can default to the >> regular heap, of course). >> >> The idea was then to use "pragma Default_Storage_Pool (null)" at the >> library root to ensure no use of default allocators, and wherever >> needed provide facilities to get a pool from the user. >> >> However, this test fails: >> >> ---8<--- >> >> pragma Restrictions (No_Secondary_Stack); -- Just to be sure in this ex. >> pragma Default_Storage_Pool (null); >> >> procedure Anon is >> >> type Holder is record >> I : aliased Integer; >> end record; >> >> type Ref (Elem : access constant Integer) is limited null record; >> >> function To_Ref (Hold : aliased Holder) return Ref is >> (Elem => Hold.I'Access); -- Error in subject here >> >> begin >> null; >> end Anon; >> >> ---8<--- >> >> There's actually no allocation being made, and I could have a Holder >> variable in the stack, and take a reference, and still no pool would >> be used at all. >> >> So it seems this pragma is too naïve. To make it into questions: >> >> Is this the pragma expected behavior or a particularity of gnat? Is >> the approach reasonable? This is my first attempt at working in a >> "restricted" Ada environment so I don't really have a clear idea of >> the preferred way to do what I want. Also, I'd like if possible to >> avoid making everything generic on the user pool. > > I'm 99% confident this is a bug in GNAT. Thanks for the analysis, that's a neat way of seeing what's going on. I guess I will report it then. I was thinking that maybe the pragma works at the access type level instead of actual allocations. That is, any access type without 'Storage_size => 0 or explicit allocator would fail. But reading 13.11.3 6/3 it seems that it is the other way around: at the point of the access type declaration either default 'Storage_Size or 'Storage_Pool is determined depending on the Default_Storage_Pool value. Though I am not a l-lawyer so... Álex. > > The repreentation of the generated code (-gnatG) for To_Ref is > > function to_ref (hold : aliased holder; to_refBIPalloc : natural; > to_refBIPstoragepool : > system__storage_pools__root_storage_pool_ptr; to_refBIPaccess : > T5b) return ref is > begin > R14b : declare > [subtype T12b is ref (hold.i'access)] > type A16b is access all T12b; > R17b : A16b := null; > if to_refBIPalloc = 1 then > R17b := A16b!(to_refBIPaccess); > elsif to_refBIPalloc = 2 then > R17b := new T12b[storage_pool = > system__secondary_stack__ss_pool]; > elsif to_refBIPalloc = 3 then > R17b := new T12b; > elsif to_refBIPalloc = 4 then > P15b : system__storage_pools__root_storage_pool renames > to_refBIPstoragepool.all; > R17b := new T12b[storage_pool = P15b]; > else > [program_error "build in place mismatch"] > end if; > R13b : T12b renames R17b.all; > R13b.elem := hold.i'access; > begin > return R13b; > end R14b; > end to_ref; > > where to_refBIPalloc is a parameter determined by the compiler. In the > case of > > H : aliased Holder := (I => 42); > R : Ref := To_Ref (H); > > it's 1, and to_refBIPaccess is R'Unrestricted_Access. > > The other cases are presumably to cope with other calling patterns > (can't imagine what), and in particular case 3 is a standard 'new', > which would be what triggers the error message. >