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target/arm: Fix AddPAC error indication

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The definition of top_bit used in this function is one higher
than that used in the Arm ARM psuedo-code, which put the error
indication at top_bit - 1 at the wrong place, which meant that
it wasn't visible to Auth.

Fixing the definition of top_bit requires more changes, because
its most common use is for the count of bits in top_bit:bot_bit,
which would then need to be computed as top_bit - bot_bit + 1.

For now, prefer the minimal fix to the error indication alone.

Fixes: 63ff0ca94cb

Backports commit 8796fe40dd30cd9ffd3c958906471715c923b341 from qemu
This commit is contained in:
Richard Henderson 2021-02-25 23:44:24 -05:00 committed by Lioncash
parent 4952920d4d
commit ce8282d9cd
1 changed files with 5 additions and 1 deletions
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6
qemu/target/arm/pauth_helper.c
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@ -300,7 +300,11 @@ static uint64_t pauth_addpac(CPUARMState *env, uint64_t ptr, uint64_t modifier,
*/
test = sextract64(ptr, bot_bit, top_bit - bot_bit);
if (test != 0 && test != -1) {
pac ^= MAKE_64BIT_MASK(top_bit - 1, 1);
/*
* Note that our top_bit is one greater than the pseudocode's
* version, hence "- 2" here.
*/
pac ^= MAKE_64BIT_MASK(top_bit - 2, 1);
}
/*