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489553dd13
The existing code in emit_call on RV64 checks that the PC-relative offset to the function fits in 32 bits before calling emit_jump_and_link to emit an auipc+jalr pair. However, this check is incorrect because offsets in the range [2^31 - 2^11, 2^31 - 1] cannot be encoded using auipc+jalr on RV64 (see discussion [1]). The RISC-V spec has recently been updated to reflect this fact [2, 3]. This patch fixes the problem by moving the check on the offset into emit_jump_and_link and modifying it to the correct range of encodable offsets, which is [-2^31 - 2^11, 2^31 - 2^11). This also enforces the check on the offset to other uses of emit_jump_and_link (e.g., BPF_JA) as well. Currently, this bug is unlikely to be triggered, because the memory region from which JITed images are allocated is close enough to kernel text for the offsets to not become too large; and because the bounds on BPF program size are small enough. This patch prevents this problem from becoming an issue if either of these change. [1]: https://groups.google.com/a/groups.riscv.org/forum/#!topic/isa-dev/bwWFhBnnZFQ [2]: |
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