I'm relying on Simon M here. I'm out of my depth!
Simon
| -----Original Message-----
| From: ghc-devs On Behalf Of Ömer Sinan
| Agacan
| Sent: 05 February 2019 13:38
| To: ghc-devs
| Subject: Re: Min closure payload size?
|
| I just came across a closure that is according to this code is not valid:
|
| >>> print *get_itbl(0x7b2870)
| $8 = {
| layout = {
| payload = {
| ptrs = 0,
| nptrs = 0
| },
| bitmap = 0,
| large_bitmap_offset = 0,
| __pad_large_bitmap_offset = 0,
| selector_offset = 0
| },
| type = 21,
| srt = 3856568,
| code = 0x404ef0
| "H\215E\360L9\370rDH\203\354\bL\211\350H\211\336H\211\307\061\300\350|\034\
| 062"
| }
|
| This is a THUNK_STATIC with 0 ptrs and nptrs in the payload.
|
| Ömer
|
| Ömer Sinan Ağacan , 4 Şub 2019 Pzt, 16:23
| tarihinde şunu yazdı:
| >
| > Hi,
| >
| > I was trying to understand why some info tables that have no ptrs and
| nptrs like
| > GCD_CAF end up with 1 nptrs in the generated info table and found this
| code in
| > Constants.h:
| >
| > /* ------------------------------------------------------------------
| -----------
| > Minimum closure sizes
| >
| > This is the minimum number of words in the payload of a
| > heap-allocated closure, so that the closure has enough room to be
| > overwritten with a forwarding pointer during garbage collection.
| > ------------------------------------------------------------------
| --------
| > */
| >
| > #define MIN_PAYLOAD_SIZE 1
| >
| > We use this in a few places in the compiler and add at least one word
| space in
| > the payload. However the comment is actually wrong, forwarding pointers
| are made
| > by tagging the info ptr field so we don't need a word in the payload for
| > forwarding pointers. I tried updating this as 0 but that caused a lot of
| test
| > failures (mostly in GHCi). I'm wondering if I'm missing anything or is it
| just
| > some code assuming min payload size 1 without using this macro.
| >
| > Any ideas?
| >
| > Ömer
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