bpf: static data: use inline asm to access static data #27589
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dylandreimerink
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Aug 25, 2023
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@yasz24 can you PTAL and see the areas where you can help in follow ups? |
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This will conflict with #28417, will wait for that to land first. |
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dst_id is often populated by LXC_ID, which is only theoretically a compile-time constant, and generally only when it is compiled using the default ep_config.h or in bpf unit tests. The actual value used for LXC_ID in the bytecode varies per endpoint, so asserting it to be a constant is not very useful. A subsequent commit will make LXC_ID evaluate to an (inlined) function call, so even the theoretical constant-ness assertion no longer holds. Signed-off-by: Timo Beckers <timo@isovalent.com>
The new static data approach is fully documented in the code. Using an inline asm block makes for a more predictable outcome in the bytecode, meaning we can simplify the substitution logic on the Go side and start using runtime-provided constants for user space dead code elimination. Signed-off-by: Timo Beckers <timo@isovalent.com> Co-authored-by: Dylan Reimerink <dylan.reimerink@isovalent.com>
Due to the new implementation of static data substitution in a prior commit, static data symbols now appear with local binding. Rename isGlobalData and only make it tolerate OBJECT-type symbols with local or global visibility. Signed-off-by: Timo Beckers <timo@isovalent.com>
To reduce the amount of potential interference on the resulting bytecode loaded into the kernel, remove .bss inlining from inlineGlobalData. Since a prior commit, all global data is now explicitly placed in .rodata.config, so symbols should never end up in .bss even if they're zero-initialized. Signed-off-by: Timo Beckers <timo@isovalent.com>
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The new static data approach is fully documented in the code. Using a volatile inline asm block makes for a more predictable outcome in the bytecode, meaning we can simplify the substitution logic on the Go side and start using runtime-provided constants for user space dead code elimination.
Part of: #27320