On Thu, 30 Sept 2021 at 06:44, David Gibson <david@gibson.dropbear.id.au> wrote:
From: Cédric Le Goater <clg@kaod.org>
The current way the mask is built can overflow with a 64-bit decrementer.
Use sextract64() to extract the signed values and remove the logic to
handle negative values which has become useless.
Cc: Luis Fernando Fujita Pires <luis.pires@eldorado.org.br>
Fixes: a8dafa525181 ("target/ppc: Implement large decrementer support for TCG")
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20210920061203.989563-5-clg@kaod.org>
Reviewed-by: Luis Pires <luis.pires@eldorado.org.br>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Hi; Coverity complains about dead code here (CID 1464061):
* On MSB edge based DEC implementations the MSB going from 0 -> 1
triggers
* an edge interrupt, so raise it here too.
*/
- if ((value < 3) ||
- ((tb_env->flags & PPC_DECR_UNDERFLOW_LEVEL) && negative) ||
- ((tb_env->flags & PPC_DECR_UNDERFLOW_TRIGGERED) && negative
- && !(decr & (1ULL << (nr_bits - 1))))) {
+ if ((signed_value < 3) ||
+ ((tb_env->flags & PPC_DECR_UNDERFLOW_LEVEL) && signed_value < 0) ||
+ ((tb_env->flags & PPC_DECR_UNDERFLOW_TRIGGERED) && signed_value < 0
+ && signed_decr >= 0)) {
(*raise_excp)(cpu);
return;
}
If signed_value < 3 then the first clause of the || evaluates as true,
and so we will definitely take the if() clause. So if we're evaluating
the second operand to the || then we know that signed_value > 3,
which means that 'signed_value < 0' is always false and in turn that
neither of the other two '||' options can be true. The whole expression
is equivalent to just "if (signed_value < 3)".
What was intended here? If this was supposed to be a no-behaviour-change
commit (apart from fixing the 64-bit case) then the condition should
have stayed as "(value < 3)", I think.