| /qemu/tests/tcg/i386/ |
| H A D | test-flags.c | e7bbb7cb71b3001c54f23c66848d84e694c47243 Wed Oct 11 13:26:40 UTC 2023 Paolo Bonzini <pbonzini@redhat.com> target/i386: introduce flags writeback mechanism
ALU instructions can write to both memory and flags. If the CC_SRC*
and CC_DST locations have been written already when a memory access
causes a fault, the value in CC_SRC* and CC_DST might be interpreted
with the wrong CC_OP (the one that is in effect before the instruction.
Besides just using the wrong result for the flags, something like
subtracting -1 can have disastrous effects if the current CC_OP is
CC_OP_EFLAGS: this is because QEMU does not expect bits outside the ALU
flags to be set in CC_SRC, and env->eflags can end up set to all-ones.
In the case of the attached testcase, this sets IOPL to 3 and would
cause an assertion failure if SUB is moved to the new decoder.
This mechanism is not really needed for BMI instructions, which can
only write to a register, but put it to use anyway for cleanliness.
In the case of BZHI, the code has to be modified slightly to ensure
that decode->cc_src is written, otherwise the new assertions trigger.
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
|
| H A D | Makefile.target | e7bbb7cb71b3001c54f23c66848d84e694c47243 Wed Oct 11 13:26:40 UTC 2023 Paolo Bonzini <pbonzini@redhat.com> target/i386: introduce flags writeback mechanism
ALU instructions can write to both memory and flags. If the CC_SRC*
and CC_DST locations have been written already when a memory access
causes a fault, the value in CC_SRC* and CC_DST might be interpreted
with the wrong CC_OP (the one that is in effect before the instruction.
Besides just using the wrong result for the flags, something like
subtracting -1 can have disastrous effects if the current CC_OP is
CC_OP_EFLAGS: this is because QEMU does not expect bits outside the ALU
flags to be set in CC_SRC, and env->eflags can end up set to all-ones.
In the case of the attached testcase, this sets IOPL to 3 and would
cause an assertion failure if SUB is moved to the new decoder.
This mechanism is not really needed for BMI instructions, which can
only write to a register, but put it to use anyway for cleanliness.
In the case of BZHI, the code has to be modified slightly to ensure
that decode->cc_src is written, otherwise the new assertions trigger.
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
|
| /qemu/target/i386/tcg/ |
| H A D | decode-new.h | e7bbb7cb71b3001c54f23c66848d84e694c47243 Wed Oct 11 13:26:40 UTC 2023 Paolo Bonzini <pbonzini@redhat.com> target/i386: introduce flags writeback mechanism
ALU instructions can write to both memory and flags. If the CC_SRC*
and CC_DST locations have been written already when a memory access
causes a fault, the value in CC_SRC* and CC_DST might be interpreted
with the wrong CC_OP (the one that is in effect before the instruction.
Besides just using the wrong result for the flags, something like
subtracting -1 can have disastrous effects if the current CC_OP is
CC_OP_EFLAGS: this is because QEMU does not expect bits outside the ALU
flags to be set in CC_SRC, and env->eflags can end up set to all-ones.
In the case of the attached testcase, this sets IOPL to 3 and would
cause an assertion failure if SUB is moved to the new decoder.
This mechanism is not really needed for BMI instructions, which can
only write to a register, but put it to use anyway for cleanliness.
In the case of BZHI, the code has to be modified slightly to ensure
that decode->cc_src is written, otherwise the new assertions trigger.
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
|
| H A D | decode-new.c.inc | e7bbb7cb71b3001c54f23c66848d84e694c47243 Wed Oct 11 13:26:40 UTC 2023 Paolo Bonzini <pbonzini@redhat.com> target/i386: introduce flags writeback mechanism
ALU instructions can write to both memory and flags. If the CC_SRC*
and CC_DST locations have been written already when a memory access
causes a fault, the value in CC_SRC* and CC_DST might be interpreted
with the wrong CC_OP (the one that is in effect before the instruction.
Besides just using the wrong result for the flags, something like
subtracting -1 can have disastrous effects if the current CC_OP is
CC_OP_EFLAGS: this is because QEMU does not expect bits outside the ALU
flags to be set in CC_SRC, and env->eflags can end up set to all-ones.
In the case of the attached testcase, this sets IOPL to 3 and would
cause an assertion failure if SUB is moved to the new decoder.
This mechanism is not really needed for BMI instructions, which can
only write to a register, but put it to use anyway for cleanliness.
In the case of BZHI, the code has to be modified slightly to ensure
that decode->cc_src is written, otherwise the new assertions trigger.
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
|
| H A D | emit.c.inc | e7bbb7cb71b3001c54f23c66848d84e694c47243 Wed Oct 11 13:26:40 UTC 2023 Paolo Bonzini <pbonzini@redhat.com> target/i386: introduce flags writeback mechanism
ALU instructions can write to both memory and flags. If the CC_SRC*
and CC_DST locations have been written already when a memory access
causes a fault, the value in CC_SRC* and CC_DST might be interpreted
with the wrong CC_OP (the one that is in effect before the instruction.
Besides just using the wrong result for the flags, something like
subtracting -1 can have disastrous effects if the current CC_OP is
CC_OP_EFLAGS: this is because QEMU does not expect bits outside the ALU
flags to be set in CC_SRC, and env->eflags can end up set to all-ones.
In the case of the attached testcase, this sets IOPL to 3 and would
cause an assertion failure if SUB is moved to the new decoder.
This mechanism is not really needed for BMI instructions, which can
only write to a register, but put it to use anyway for cleanliness.
In the case of BZHI, the code has to be modified slightly to ensure
that decode->cc_src is written, otherwise the new assertions trigger.
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
|
| /qemu/target/i386/ |
| H A D | cpu.h | e7bbb7cb71b3001c54f23c66848d84e694c47243 Wed Oct 11 13:26:40 UTC 2023 Paolo Bonzini <pbonzini@redhat.com> target/i386: introduce flags writeback mechanism
ALU instructions can write to both memory and flags. If the CC_SRC*
and CC_DST locations have been written already when a memory access
causes a fault, the value in CC_SRC* and CC_DST might be interpreted
with the wrong CC_OP (the one that is in effect before the instruction.
Besides just using the wrong result for the flags, something like
subtracting -1 can have disastrous effects if the current CC_OP is
CC_OP_EFLAGS: this is because QEMU does not expect bits outside the ALU
flags to be set in CC_SRC, and env->eflags can end up set to all-ones.
In the case of the attached testcase, this sets IOPL to 3 and would
cause an assertion failure if SUB is moved to the new decoder.
This mechanism is not really needed for BMI instructions, which can
only write to a register, but put it to use anyway for cleanliness.
In the case of BZHI, the code has to be modified slightly to ensure
that decode->cc_src is written, otherwise the new assertions trigger.
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
|