99d5579656
The yieldThread function implements MIPS's yield instruction, and had a
if condition in it, (src_reg && !yield_mask != 0), which upset clang. When
originally committed, this check read (src_reg & !yield_mask != 0), but
apparently as part of a cleanup sweep a long time ago, it was assumed
that the & was being used as a logical operator and was turned into &&.
Reading the actual description of what the yield instruction is supposed
to do, if src_reg is positive (it is at this point in the function),
then it's supposed to be treated as a bitvector. The YQMask register,
what gets passed in as yield_mask, can have bits set in it which mask
bits that might be set in src_reg, and if any are still set, the an
interrupt should happen, as implemented by the body of the if.
From this description, it's apparent that what the original code was
*trying* to do was to use yield_mask to mask any set bits in src_reg,
and then if any bits were left go into the body. The original author
used ! as a bitwise negating operator since what they *wanted* to do was
to block any bits in src_reg where yield_mask *is* set, and let through
any where yield_mask *is not* set. The & would do that, but only with a
bitwise negated yield_mask. Hence:
if ((src_reg & ~yield_mask) != 0) {
...
}
Change-Id: I30d0a47992750adf78c8aa0c28217da187e0cbda
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40957
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Boris Shingarov <shingarov@gmail.com>
This is the gem5 simulator. The main website can be found at http://www.gem5.org A good starting point is http://www.gem5.org/about, and for more information about building the simulator and getting started please see http://www.gem5.org/documentation and http://www.gem5.org/documentation/learning_gem5/introduction. To build gem5, you will need the following software: g++ or clang, Python (gem5 links in the Python interpreter), SCons, SWIG, zlib, m4, and lastly protobuf if you want trace capture and playback support. Please see http://www.gem5.org/documentation/general_docs/building for more details concerning the minimum versions of the aforementioned tools. Once you have all dependencies resolved, type 'scons build/<ARCH>/gem5.opt' where ARCH is one of ARM, NULL, MIPS, POWER, SPARC, or X86. This will build an optimized version of the gem5 binary (gem5.opt) for the the specified architecture. See http://www.gem5.org/documentation/general_docs/building for more details and options. The basic source release includes these subdirectories: - configs: example simulation configuration scripts - ext: less-common external packages needed to build gem5 - src: source code of the gem5 simulator - system: source for some optional system software for simulated systems - tests: regression tests - util: useful utility programs and files To run full-system simulations, you will need compiled system firmware (console and PALcode for Alpha), kernel binaries and one or more disk images. If you have questions, please send mail to gem5-users@gem5.org Enjoy using gem5 and please share your modifications and extensions.