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Re: [PATCH v4 4/4] meson: Warn when TCI is selected but TCG backend is a

From: Stefan Weil
Subject: Re: [PATCH v4 4/4] meson: Warn when TCI is selected but TCG backend is available
Date: Wed, 27 Jan 2021 21:49:52 +0100
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:78.0) Gecko/20100101 Thunderbird/78.6.1

Am 27.01.21 um 20:52 schrieb Alex Bennée:

For example - debian-buster (arm64) running ffmpeg:

   alex.bennee@8cd150a4b35d:~/lsrc/qemu.git/builds/all.tci$ ./qemu-aarch64 
/usr/bin/ffmpeg -i theora.mkv theora.webm
   TODO ../../tcg/tci.c:882: tcg_qemu_tb_exec()
   ../../tcg/tci.c:882: tcg fatal error
   qemu: uncaught target signal 11 (Segmentation fault) - core dumped
   Segmentation fault (core dumped)

Thanks. All I tried to say is that I prefer to replace those TODO statements by working code as soon as there was a case which triggers them. Most of those TODO statements are very easy to implement, so anyone can add them when he/she detects a missing one. If I get information about a scenario which triggers a missing TODO, I'll fix that of course. I just don't want to add that missing code blindly.

Using `make check-tcg` helped finding and fixing one of them, future improved CI checks can find more, and so can examples like the one above. The error message tci.c:882 is INDEX_op_ld8s_i64 (https://github.com/qemu/qemu/blob/master/tcg/tci.c#L882). The missing code is nearly identical to the existing code for INDEX_op_ld8u_i64, but with *(int8_t *) instead of *(uint8_t *), so maybe you can try that and confirm whether it fixes the reported problem. Otherwise I'll try to reproduce it with any mkv file.

I recently tried running tesseract with qemu-x86_64 because I had expected that it might trigger some unimplemented TCG opcodes. Instead it showed a general problem for native TCG: qemu-x86_64 allocates too much memory for tesseract and gets killed by the Linux kernel OOM handler.



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