Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC

Commits:

• a5e4b7d9
  by Ben Gamari at 2025-08-13T21:02:18-04:00

  rts: Clarify rationale for undefined atomic wrappers
  
  Since c06e3f46d24ef69f3a3d794f5f604cb8c2a40cbc the RTS has declared
  various atomic operation wrappers defined by ghc-internal as undefined.
  While the rationale for this isn't clear from the commit message, I
  believe that this is necessary due to the unregisterised backend.
  Specifically, the code generator will reference these symbols when
  compiling RTS Cmm sources.
  

2 changed files:

• rts/external-symbols.list.in
• rts/rts.cabal

Changes:

 ghczminternal_GHCziInternalziWord_W32zh_con_info

 ghczminternal_GHCziInternalziWord_W64zh_con_info

 ghczminternal_GHCziInternalziStable_StablePtr_con_info

+ghczminternal_GHCziInternalziStackziCloneStack_StackSnapshot_closure

+

+#if 0

+N.B. These symbols are defined in ghc-internal and may be referenced by the

+unregisterised code-generator when compiling RTS Cmm sources.

+#endif

 hs_atomic_add8

 hs_atomic_add16

 hs_atomic_add32

 hs_atomicwrite16

 hs_atomicwrite32

 hs_atomicwrite64

-ghczminternal_GHCziInternalziStackziCloneStack_StackSnapshot_closure

 -- GHC already does `-undefined dynamic_lookup`, so we just do that for now, but

 -- we might try to get more precise with `-U` in the future.

 --

--- Note that the RTS also `-u`s some atomics symbols that *are* defined --- and

--- defined within the RTS! It is not immediately clear why this is needed. This

--- dates back to c06e3f46d24ef69f3a3d794f5f604cb8c2a40cbc which mentions a build

--- failure that it was suggested that this fix, but the precise reasoning is not

--- explained.

+-- Note that the RTS also `-u`s some symbols for atomic operations that *are* defined

+-- by `ghc-internal`. This is needed when the RTS is compiled when the RTS is

+-- compiled with, e.g., the unregisterised backend since the code-generator will

+-- reference these symbols when compiling atomic primops in Cmm sources.