target/mips: Fix handling of LL/SC instructions after 7dd547e5

After 7dd547e5 the env->llval value
is loaded as an unsigned value (instead of sign-extended as before).
Therefore, the CMPXCHG in gen_st_cond() in translate.c fails if the
sign bit is set in the loaded value.

Fix this by sign-extending the llval value for the 32-bit case.

I discovered this issue because FreeBSD MIPS64 was looping forever
in an atomic helper function when trying to start /sbin/init.
Signed-off-by: NAlex Richardson <Alexander.Richardson@cl.cam.ac.uk>
Fixes: 7dd547e5 ("target/mips: Use cpu_*_mmuidx_ra instead of MMU_MODE*_SUFFIX")
Buglink: https://bugs.launchpad.net/qemu/+bug/1861605
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Aleksandar Markovic <amarkovic@wavecomp.com>
Cc: Aleksandar Rikalo <aleksandar.rikalo@rt-rk.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: NJames Clarke <jrtc27@jrtc27.com>
Signed-off-by: NAleksandar Markovic <amarkovic@wavecomp.com>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Tested-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200202153409.28534-1-jrtc27@jrtc27.com>

target/mips/op_helper.c

@@ -305,7 +305,7 @@ static inline hwaddr do_translate_address(CPUMIPSState *env,
     }
 }
 
-#define HELPER_LD_ATOMIC(name, insn, almask)                                  \
+#define HELPER_LD_ATOMIC(name, insn, almask, do_cast)                         \
 target_ulong helper_##name(CPUMIPSState *env, target_ulong arg, int mem_idx)  \
 {                                                                             \
     if (arg & almask) {                                                       \
@@ -316,12 +316,12 @@ target_ulong helper_##name(CPUMIPSState *env, target_ulong arg, int mem_idx)  \
     }                                                                         \
     env->CP0_LLAddr = do_translate_address(env, arg, 0, GETPC());             \
     env->lladdr = arg;                                                        \
-    env->llval = cpu_##insn##_mmuidx_ra(env, arg, mem_idx, GETPC());          \
+    env->llval = do_cast cpu_##insn##_mmuidx_ra(env, arg, mem_idx, GETPC());  \
     return env->llval;                                                        \
 }
-HELPER_LD_ATOMIC(ll, ldl, 0x3)
+HELPER_LD_ATOMIC(ll, ldl, 0x3, (target_long)(int32_t))
 #ifdef TARGET_MIPS64
-HELPER_LD_ATOMIC(lld, ldq, 0x7)
+HELPER_LD_ATOMIC(lld, ldq, 0x7, (target_ulong))
 #endif
 #undef HELPER_LD_ATOMIC
 #endif