Modifying the "StgHeader" struct

[Matthew Pickering]

Hi Adithya,

It seems that eras profiling mode allows you to determine this information.
In eras profiling the era the object is created is stored in the profiling
header, you can automatically increment the era with the
--automatic-era-increment at each major collection, you can work out "how
many collections an object has been live" by subtracting the current era
from the era the object was created.

Cheers,

Matt

On Sun, 25 Feb 2024, 15:43 Csaba Hruska, <csaba.hruska at gmail.com> wrote:

> Hi,
> Are you using profiling mode?
> Regards,
> Csaba
>
> On Sun, Feb 25, 2024 at 1:59 PM Adithya Kumar <adi.obilisetty at gmail.com>
> wrote:
>
>> Hello,
>>
>> I want to add a field for collecting information about the number of GCs a
>> particular heap object survived.
>>
>> I've done the following to implement this:
>> - Add a field "StgWord gc_id" to struct "StgHeader" and "StgThunkHeader"
>> - Update "SET_HDR" macro in "ClosureMacros.h" to update the "gc_id"
>> - Update the "closureTypeHeaderSize" function in "Heap/ClosureTypes.hs" to
>>   account for that 1 extra word.
>>
>> Compilation leads to a segmentation fault. The stage 2 compiler is built.
>> But
>> usage of it leads to a segmentation fault.
>>
>> Build output:
>> ```
>> chmod +x
>> inplace/bin/ghc-stage2
>> "inplace/bin/ghc-stage2" -hisuf dyn_hi -osuf  dyn_o -hcsuf dyn_hc -fPIC
>> -dynamic  -O0 -H64m -Wall      -hide-all-packages -package-env - -i
>> -iutils/check-api-annotations/.
>> -iutils/check-api-annotations/dist-install/build
>> -Iutils/check-api-annotations/dist-install/build
>> -iutils/check-api-annotations/dist-install/build/check-api-annotations/autogen
>> -Iutils/check-api-annotations/dist-install/build/check-api-annotations/autogen
>>     -optP-include
>> -optPutils/check-api-annotations/dist-install/build/check-api-annotations/autogen/cabal_macros.h
>> -package-id Cabal-3.2.1.0 -package-id base-4.14.3.0 -package-id
>> containers-0.6.5.1 -package-id directory-1.3.6.0 -package-id
>> ghc-8.10.7.20240224 -Wall -XHaskell2010  -no-user-package-db -rtsopts
>> -Wnoncanonical-monad-instances  -outputdir
>> utils/check-api-annotations/dist-install/build   -c
>> utils/check-api-annotations/./Main.hs -o
>> utils/check-api-annotations/dist-install/build/Main.dyn_o
>> utils/check-api-annotations/ghc.mk:18: recipe for target
>> 'utils/check-api-annotations/dist-install/build/Main.dyn_o' failed
>> make[1]: *** [utils/check-api-annotations/dist-install/build/Main.dyn_o]
>> Segmentation fault (core dumped)
>> Makefile:123: recipe for target 'all' failed
>> make: *** [all] Error 2
>> ```
>>
>> Is there any other place I've missed follow-up modifications?
>>
>> I appreciate any help provided.
>>
>> Best,
>> Adithya
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