I don't like using negative numbers in C code because it's not idiomatic
for the language and I'm pedantic :)
The C compiler uses a XILF instruction to implement to compliment
operator and does the AND with a NRK instruction. The distinct operand
facility is interesting.
It's for register constraint relief. I wonder how much it's used by
assembler programmers?
aligned_malloc
000006 | DS 0D
000006 | STM r6,r10,1928(r4)
000006 | LAY r4,-128(,r4)
End of Prolog
000011 | L r6,=A(malloc)(,r5,12)
000010 | ALHSIK r10,r2,H'-1'
000010 | ALHSIK r0,r2,H'3'
000007 | * {
000008 | * void * ptr = NULL;
000008 | LA r8,0
000011 | L r5,=A(malloc)(,r5,8)
000009 | * // allocate storage area with space for an extra
pointer and alignment
000010 | * size += sizeof(void *) + (align - 1);
000010 | ALRK r9,r1,r0
000011 | * void * mem = malloc(size);
000011 | LR r1,r9
000011 | BASR r7,r6
000011 | NOP 6
000012 | * if (mem) {
000012 | CIJE r3,H'0',@2L2
000013 | * // point to the start of the aligned storage
to return
000014 | * ptr = (void **)((uintptr_t)(mem + size) &
~(align - 1));
000014 | LA r0,#AddressShadow(r9,r3,0)
000014 | XILF r10,F'-1'
000014 | NRK r8,r0,r10
000015 | * // store the address of the allocated memory
prior to the aligned storage
000016 | * ((void **) ptr)[-1] = mem;
000016 | STY r3,(*)void*(,r8,-4)
000016 | @2L2 DS 0H
000017 | * }
000018 | * return ptr;
000018 | LR r3,r8
000019 | * }
000019 | @2L3 DS 0H
Start of Epilog
000019 | LM r7,r10,2060(r4)
000019 | LA r4,128(,r4)
000019 | B 4(,r7)
Start of Epilog
000017 | LM r7,r9,2060(r4)
000017 | LA r4,128(,r4)
000017 | B 4(,r7)
On 19/07/2018 10:43 PM, Steve Smith wrote:
Thank-you Mr. Relson!
Oddly enough, in rerunning my test, it seems that it fails considerably
less than half the time. That is, it usually aligns on a 16-byte
boundary. This test version is configured to allocate the cpool anchor and
extent, plus four 160-byte buffers. This is to stress-test buffer
exhaustion logic. The production version uses 4091* buffers, making the
total space just under 640KB (which as we all know, should be enough for
anybody). That has never failed to align correctly.
* The idea is to *avoid* buffer exhaustion, and presently, this seems to be
enough.
Re specification of rounding mask: I do think -16, -8, etc. are an elegant
way to specify these, particularly as they correlate to 16-byte, 8-byte,
etc. boundaries. I sure wish they were usable with NILL and NILF.
Well, I decided to check before complaining... and (surprise!):
0000028C 0000 0000 00000000 481 NILL
R15,-4
** ASMA031E Invalid immediate or mask
field
00000290 C0FB FFFF FFF0 00000000 482 NILF
R15,-16
483
*
Sigh.
sas
On Thu, Jul 19, 2018 at 8:01 AM, Peter Relson <[email protected]> wrote:
Problems:
1. Undocumented requirement to quad-word align CPOOL anchor and/or
extent
in 64-bit mode (and actually undocumented alignment requirements for
all).
2. Unable to guarantee quad-word alignment with malloc.
I will get the first taken care of. The anchor does not need to be
quad-word aligned.
For the second, as has been pointed out in C syntax but I think not in
words, you would do what everyone used to do prior to STARTBDY keyword of
GETMAIN / STORAGE OBTAIN -- round the start address up to the necessary
boundary, having gotten an additional 8 if you need the length to be some
specific value (or 15 if you do are not guaranteed that the area will at
least be on a doubleword boundary).
The rounding is typically "Add 15, AND with -16".
Peter Relson
z/OS Core Technology Design
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