Re: [PATCH v2] perf docs: Correct JIT_CODE_UNWINDING_INFO specification

[sashiko-bot@kernel.org]

> The JIT_CODE_UNWINDING_INFO description places the EH Frame Header before
> the EH Frame. However, jit_add_eh_frame_info() uses the beginning of the
> unwinding data for .eh_frame and the trailing eh_frame_hdr_size bytes for
> .eh_frame_hdr.
> 
> Correct the unwinding_data description and the eh_frame_hdr_size field
> description to match the layout consumed by perf.
> 
> Also document that an unwinding record precedes and applies to the next
> JIT_CODE_LOAD record. perf caches the unwinding data and uses it when
> processing that load record.
> 
> Revise the mapped_size note to describe frame-pointer-based unwinding as
> a possibility depending on the backend and valid frame pointers in the
> generated code.
> 
> The libunwind-specific use case still matters: its EH Frame Header fields
> through fde_count are read directly from the ELF file, while lookup-table
> and EH Frame accesses require a mapping covering those addresses. An
> empty lookup table can trigger frame-pointer-based unwinding fallback
> without mapping the unwinding data. This does not impose the same access
> requirements on other unwinding backends.
> 
> Signed-off-by: Letian Jiang <letian.jiang@outlook.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/CYXPR84MB347640EF284BED04EADB0B4A826C2@CYXPR84MB3476.NAMPRD84.PROD.OUTLOOK.COM?part=1