julia: avoid access into Julia structs in Julia >= 1.6 #4086
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
fingolfin
added
topic: kernel
release notes: not needed
rbehrends
reviewed
Jul 30, 2020
fingolfin
force-pushed
the
mh/julia-no-struct-access
branch
3 times, most recently
from
b6fca4f to
51bb7c3
Compare
wilfwilson
approved these changes
Aug 11, 2020
Member
wilfwilson
left a comment
wilfwilson
left a comment
There was a problem hiding this comment.
Looks reasonable to me, given the commit messages.
Member
Author
|
This needs to be updated to reflect the changes in JuliaLang/julia#36823 |
It was previously turned off as an unintended side effect of adding `--disable-Werror` to the configure flags (as the `libuv.h` from Julia introduced some warnings)
We currently access members of various structs provided by Julia (of type jl_task_t resp. jl_tls_t). This introduces an unwanted binary dependency on the precise Julia version GAP was compiled against; i.e. because of these, a binary compiled against Julia 1.3 cannot be used with Julia 1.5 To avoid this, the Julia folks merged some new APIs: - `jl_active_task_stack` allows us to avoid access to `task->copy_stack` - `jl_get_safe_restore` and `jl_set_safe_restore` allow us to avoid direct access to `tls->safe_restore` In order to simultaneously support older and newer Julia versions, we use two tricks: - we don't link during compile time against the new APIs; instead we use `dlsym` to query at runtime if they are available, and only then call them (this introduces as small overhead at the call sites, but this is negligible) - for `task->copy_stack` this is enough as its offset has been unchanged between Julia 1.3 and Julia 1.6 - for `tls->safe_restore`, the offset *did* change once between Julia 1.4 and 1.5. Luckily, the change is the same on all 64 bit platforms: the offset shifted by 8. To adjust for that, we compare the Julia version used to compile GAP against that which runs GAP to compute a suitable offset for adjusting access to `tls->safe_restore`.
fingolfin
force-pushed
the
mh/julia-no-struct-access
branch
from
51bb7c3 to
5fa6e0b
Compare
Member
Author
|
Rebased and adapted to match the final version of @ThomasBreuer ping just FYI |
rbehrends
approved these changes
Oct 7, 2020
Member
Author
|
Backported to stabled-4.11 in ef2ad98 |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
4 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
We currently access members of various structs provided by Julia (of type jl_task_t resp. jl_tls_t). This introduces an unwanted binary dependency on the precise Julia version GAP was compiled against; i.e. because of these, a binary compiled against Julia 1.3 cannot be used with Julia 1.5
To avoid this, the Julia folks merged some new APIs:
jl_active_task_stackallows us to avoid access totask->copy_stack(see Add jl_active_task_stack to gcext API JuliaLang/julia#36823)jl_get_safe_restoreandjl_set_safe_restoreallow us to avoid direct access totls->safe_restore(see Accessors for current_task, safe_restore in TLS JuliaLang/julia#36064)In order to simultaneously support older and newer Julia versions, we use two tricks:
dlsymto query at runtime if they are available, and only then call them (this introduces as small overhead at the call sites, but this is negligible)task->copy_stackthis is enough as its offset has been unchanged between Julia 1.3 and Julia 1.6tls->safe_restore, the offset did change once between Julia 1.4 and 1.5. Luckily, the change is the same on all 64 bit platforms: the offset shifted by 8. To adjust for that, we compare the Julia version used to compile GAP against that which runs GAP to compute a suitable offset for adjusting access totls->safe_restore.