Fix decoding of bytecode instructions on ARM generated on x86-64

Due to the difference of sign of the char type, byte code is encoded
differently on x86-64 than if it was on ARM and it also is decoded
differently. The problem at hand here was that negative jumps were
encoded as two-byte instructions (opcode and negative offset as byte) on
x86-64 when qmlcachegen is run. At run-time the negative offset was read
into a char type and consequently interpreted as a positive jump,
leading to crashes.

The explicit use of qint8 as signed byte type in encoding/decoding
sensitive parts avoids the decoding issue and should also result in
consistent encoding.

The added auto-test is (among other configurations) run in the CI under
qemu, which means the x86-64 host-built qmlcachegen will generate byte
code and the tst_qmlcachegen ARM binary will run under qemu and
reproduce this scenario.

Task-number: QTBUG-65521
Change-Id: I615628f53475dad38a41095c6e7ffea0c34d58ac
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

0 files changed, 0 insertions, 0 deletions