3099fe8081
This reverts commit 9083892277.
Reason for revert: performance regression on android-pixel6-perf-pgo: https://screenshot.googleplex.com/6yxbc7zZDcZbvKw
Original change's description:
> orderfile: Remove the patching step
>
> Remove the 'Patch Orderfile' step from the Orderfile Generator. Replace
> it with a simpler step 'Add dummy functions'. It adds the following
> symbols to the beginning and the end of the orderfile, just like the
> current orderfile patching step does:
> * dummy_function_start_of_ordered_text
> * dummy_function_end_of_ordered_text
>
> The symbol `__cxx_global_var_init` is currently added along with the
> symbols marking begin/end of the ordered address range. While the latter
> symbols are important for correctness at runtime, the former does
> not exist these days. It used to be a large and uninstrumented symbol.
> Remove mentions of it in orderfiles.
>
> Note: This change does _not_ remove generation of the unpatched
> orderfile and uploading it to the cloud storage. Leaving it as TODO for
> a separate change. The only difference remaining between the normal and
> the 'unpatched' orderfile after this change would be the presence of the
> dummy functions mentioned above.
>
> == Observation(s) from running locally
>
> About 900 symbols from the orderfile that cannot be found in the
> uninstrumented binary because of the known problem [1]. The current
> 'patching' step does not fix this problem. There is, however, a
> possibility to mitigate the problem with another style of patching,
> which is not infra-friendly because it requires two builds with
> different configuration on the same builder.
>
> A few dozen symbols from the orderfile appear at 2+ offsets in the
> binary. I think it could be in part because of the DFM splitting, but I
> am not sure. It would be nice to investigate. There is one example of
> such symbol: ReadHuffmanCode. It is defined by brotli and libwebp (both
> in third_party), and they are static symbols only referenced from the
> same file where they are defined.
>
> [1] crbug.com/356360613:
> "Teach orderfile generator to respect suffixed function names
> from LTO"
>
> Bug: 340534475
> Change-Id: Icddd3b84576cfe76bfb652fe856aac3d2701dce6
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5782742
> Reviewed-by: Peter Wen <wnwen@chromium.org>
> Commit-Queue: Peter Wen <wnwen@chromium.org>
> Reviewed-by: Rasika Navarange <rasikan@google.com>
> Cr-Commit-Position: refs/heads/main@{#1341171}
Bug: 340534475
Change-Id: I08d2865a5758c2318bf21730a0232f1465cfcc96
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5796046
Commit-Queue: Egor Pasko <pasko@chromium.org>
Auto-Submit: Egor Pasko <pasko@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1343395}
v8
@ 64a21d7ad7
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