Hi, Adding a new way that changes heap closure representation won't be trivial. Handling of the profiling way is very ad-hoc. Did you update the `deriveConstants` utils and `ghc:GHC.Runtime.Heap.Layout.*HdrSize` to take into account your new optional field? Sylvain On 18/03/2024 08:47, Adithya Kumar wrote:

Hey folks,

I'm adding a field to "StgHeader" under a flag.

``` typedef struct {     const StgInfoTable* info; #if defined(NEW_WAY)     StgWord             new_field; #endif #if defined(PROFILING)     StgProfHeader         prof; #endif } StgHeader;

typedef struct {     const StgInfoTable* info; #if defined(NEW_WAY)     StgWord             new_field; #endif #if defined(PROFILING)     StgProfHeader         prof; #endif     StgSMPThunkHeader     smp; } StgThunkHeader; ```

Follow-up changes: ==================

The following are the additional changes I've made following the `PROFILING` flag:

Similar to `PROF_HDR_FIELDS` macro, I've added `NEW_HDR_FIELDS` macro:

``` #if defined(NEW_WAY) #define NEW_HDR_FIELDS(w_,hdr) w_ hdr, #else #define NEW_HDR_FIELDS(w_,hdr) /* Nothing */ #endif ``` and updated the required stg code accordingly following the changes from `PROF_HDR_FIELDS`.

I've also updated `GHC.Exts.Heap.ClosureTypes.closureTypeHeaderSize` accordingly.

Error: ======

I'm greeted with the following error, ``` ASSERTION FAILED: file rts/StgStartup.cmm, line 100 ```

Basically, the following assert fails ``` #define CHECK_SENSIBLE_REGS()                           \     ASSERT(Hp != 0);                                    \     ASSERT(HpAlloc == 0);                               \     ASSERT(Sp != 0);                                    \     ASSERT(SpLim != 0);                                 \     ASSERT(SpLim - WDS(RESERVED_STACK_WORDS) <= Sp); ```

More context for the error: ===========================

Values for the correct version: ``` Hp      283468906488 HpAlloc 0 Sp      283468911440 SpLim   283468910784 SpLim - WDS(RESERVED_STACK_WORDS) 1069080 ```

Values with the changes: ``` Hp      283468906488 HpAlloc 0 Sp      7532120 SpLim   9301536 SpLim - WDS(RESERVED_STACK_WORDS) 9301368 ```

I recorded these values by calling a C print from the Cmm code.

Clearly, my changes messed up a lot of things. How do I go about this now? The past 2 weeks I've only been looking at a lot of ghc code. If any more additional context is required I can provide it.

Best, Adithya

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