> There is no expectation. There is no concept of the provider "formatting it".
Conventional behavior is for programs to store a back pointer after acquiring a new save area, and to store an EBCDIC identifier if appropriate. Is that not formatting. However, I think I see the issue. The called program could store a forward pointer at offset 8 and 32-bit registers at offset 12, or could store grande registers, with no way to determine which. Is that the issue?. -- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Assembler List [ASSEMBLER-LIST@LISTSERV.UGA.EDU] on behalf of Peter Relson [rel...@us.ibm.com] Sent: Thursday, January 27, 2022 8:55 AM To: ASSEMBLER-LIST@LISTSERV.UGA.EDU Subject: Re: Saving Caller's 64-bit Registers Shmuel wrote >For running forward, it's a bit stickier. Is a program providing a >144 byte save area expected to format it as FxSA? As I wrote previously, you cannot in general "run forward". You could if you know exactly what the target programs are doing (which is unlikely unless you own them). There is no expectation. There is no concept of the provider "formatting it". The provider "provides it". The target "uses it". It is not in general knowable how the target chose to "use it". The target could be a routine that expects 72 bytes and uses the first 72 bytes only (including putting the next address at +8). It could be a routine that expects 144 bytes in which case it would likely use it according to the conventions (incuding putting the next address at +x'88').. Shmuel wrote <snip> > A program that saves its caller's registers in standard 72-byte format > is expected to set offset 4 of the save area that it obtains to the address > of the previous save area, regardless of the size of save area that it provides. That's not what the manual says. A program that saves the callers registers in a 72-byte save area and alters ARs or the top halve of GRs is expected to save them in a new F5SA or F8SA </snip> There is no conflict. The manual section referred to is not what Tom was referring to. A program that "saves its caller's registers in standard 72-byte format" is not one that (also) saves ARs and/or high halves. That would be a program that "saves its caller's low halves in standard 72-byte format and also saves ARs and/or high halves". And, yes, such a program would (if following the conventions) be using F5SA/F8SA. The main important thing, as has been mentioned so many times, is that the provider of the save area provides space. The provider does not dictate how that space is to be used. The conventions are such that the uses do not conflict with respect to being able to locate the previous pointer. A general routine to format save areas does so. It looks at the value at +4 to decide if that is the previous pointer or if the previous pointer is at +x'88'. Peter Relson z/OS Core Technology Design
