julia: avoid access into Julia structs in Julia >= 1.6 #4086
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rbehrends
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Jul 30, 2020
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wilfwilson
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Aug 11, 2020
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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`.
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Rebased and adapted to match the final version of @ThomasBreuer ping just FYI |
rbehrends
approved these changes
Oct 7, 2020
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Backported to stabled-4.11 in ef2ad98 |
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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.