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authorChristian Krinitsin <mail@krinitsin.com>2025-07-03 16:27:09 +0000
committerChristian Krinitsin <mail@krinitsin.com>2025-07-03 16:27:09 +0000
commit4d9e26c0333abd39bdbd039dcdb30ed429c475ba (patch)
tree4010d5fb3e8bc48c110a2c1ff2a16b8648cb86bb /results/classifier/accel-gemma3:12b/kvm/1603779
parent5541099586dbd6018574cb44e1934907c121526f (diff)
downloademulator-bug-study-4d9e26c0333abd39bdbd039dcdb30ed429c475ba.tar.gz
emulator-bug-study-4d9e26c0333abd39bdbd039dcdb30ed429c475ba.zip
add gemma accelerator classification results
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+
+AC97 can allocate ~500MB of host RAM
+
+While working with qtest test cases generated via fuzzing with QEMU 2.5.0, I discovered some odd behavior for the AC97 virtual device with qemu-system-i386. If AC97_MIC_ADC_RATE is set to the value of 1, the QEMU process allocates over 500MB of additional host RAM. You probably would not normally notice this on a modern PC, except that I was using a "ulimit" command to restrict the maximum amount of virtual memory allowed for the QEMU process, so the process would crash with a SIGTRAP (signal 5) on the failed memory allocation.
+
+My minimized qtest code to reproduce the issue is:
+
+static void test_crash(void)
+{
+  uint64_t barsize;
+  dev = get_device();
+
+  dev_base[0] = qpci_iomap(dev, 0, &barsize);
+  dev_base[1] = qpci_iomap(dev, 1, &barsize);
+  qpci_device_enable(dev);
+  qpci_io_writew(dev, dev_base[0]+0x32, 0x00000001);
+} 
+
+I ran a "ulimit -sv 650000" command and then launched the tests/ac97-test binary with this crash test case included in it. I can then see the QEMU process crash on an allocation of 722538464 bytes. I can gradually increase the ulimit memory limit to ~1200000 and then no longer see the issue, hence my estimate of 500 MB of RAM allocated by the device.
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