LL/SC broken for MIPS after 7dd547e5ab6b31e7a0cfc182d3ad131dd55a948f

Bug #1861605 reported by Alexander Richardson on 2020-02-02
6
This bug affects 1 person
Affects Status Importance Assigned to Milestone
QEMU
Undecided
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Bug Description

In that commit the env->llval value is loaded as an unsigned value (instead of sign-extended as before and therefore the CMPXCHG in gen_st_cond() in translate.c fails.

I have committed a fix for this issue as https://github.com/qemu/qemu/commit/6ff8dec97f1a105d0da96c67ee24c75e437df162

An alternative solution would be to change the cmpxchg line to perform a non-sign-extended compare, i.e. replace
    tcg_gen_atomic_cmpxchg_tl(t0, cpu_lladdr, cpu_llval, val,
                              eva ? MIPS_HFLAG_UM : ctx->mem_idx, tcg_mo);
with
    tcg_gen_atomic_cmpxchg_tl(t0, cpu_lladdr, cpu_llval, val,
                              eva ? MIPS_HFLAG_UM : ctx->mem_idx, tcg_mo & ~MO_SIGN);

However, that change does not fix the fact that the result of ll is no longer sign-extended, therefore I think adding a cast in the helpers is better.

I cannot send this patch to the QEMU mailing list as I am not able to setup git-send-email.
Feel free to apply this commit or the alternative solution.

Thomas Huth (th-huth) wrote :
Changed in qemu:
status: New → Fix Committed
Changed in qemu:
status: Fix Committed → Fix Released
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