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svc: Correct always true assertion case in SetThreadCoreMask 

The reason this would never be true is that ideal_processor is a u8 and
THREADPROCESSORID_DEFAULT is an s32. In this case, it boils down to how
arithmetic conversions are performed before performing the comparison.

If an unsigned value has a lesser conversion rank (aka smaller size)
than the signed type being compared, then the unsigned value is promoted
to the signed value (i.e. u8 -> s32 happens before the comparison). No
sign-extension occurs here either.

An alternative phrasing:

Say we have a variable named core and it's given a value of -2.

u8 core = -2;

This becomes 254 due to the lack of sign. During integral promotion to
the signed type, this still remains as 254, and therefore the condition
will always be true, because no matter what value the u8 is given it
will never be -2 in terms of 32 bits.

Now, if one type was a s32 and one was a u32, this would be entirely
different, since they have the same bit width (and the signed type would
be converted to unsigned instead of the other way around) but would
still have its representation preserved in terms of bits, allowing the
comparison to be false in some cases, as opposed to being true all the
time.

---

We also get rid of two signed/unsigned comparison warnings while we're
at it.
This commit is contained in:
Lioncash 2018-07-19 14:36:22 -04:00
parent bbc31ba6af
commit b879fb84a2
1 changed files with 4 additions and 3 deletions
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7
src/core/hle/kernel/svc.cpp
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@ -795,8 +795,9 @@ static ResultCode SetThreadCoreMask(Handle thread_handle, u32 core, u64 mask) {
return ERR_INVALID_HANDLE; return ERR_INVALID_HANDLE;
} }
if (core == THREADPROCESSORID_DEFAULT) { if (core == static_cast<u32>(THREADPROCESSORID_DEFAULT)) {
ASSERT(thread->owner_process->ideal_processor != THREADPROCESSORID_DEFAULT); ASSERT(thread->owner_process->ideal_processor !=
static_cast<u8>(THREADPROCESSORID_DEFAULT));
// Set the target CPU to the one specified in the process' exheader. // Set the target CPU to the one specified in the process' exheader.
core = thread->owner_process->ideal_processor; core = thread->owner_process->ideal_processor;
mask = 1ull << core; mask = 1ull << core;
@ -811,7 +812,7 @@ static ResultCode SetThreadCoreMask(Handle thread_handle, u32 core, u64 mask) {
if (core == OnlyChangeMask) { if (core == OnlyChangeMask) {
core = thread->ideal_core; core = thread->ideal_core;
} else if (core >= Core::NUM_CPU_CORES && core != -1) { } else if (core >= Core::NUM_CPU_CORES && core != static_cast<u32>(-1)) {
return ResultCode(ErrorModule::Kernel, ErrCodes::InvalidProcessorId); return ResultCode(ErrorModule::Kernel, ErrCodes::InvalidProcessorId);
} }