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401bf46779
Using get_address() with register identifiers comming from an "r" field is wrong: if the "r" field designates "r0", we don't read the content and instead assume 0 - which should only be applied when the register was specified via "b" or "x". PoP 5-11 "Operand-Address Generation": "A zero in any of the B1, B2, X2, B3, or B4 fields indicates the absence of the corresponding address component. For the absent component, a zero is used in forming the intermediate sum, regardless of the contents of general register 0. A displacement of zero has no special significance." This BUG became visible for CSPG as generated by LLVM-12 in the upstream Linux kernel (v5.11-rc2), used while creating the linear mapping in vmem_map_init(): Trying to store to address 0 results in a Low Address Protection exception. Debugging this was more complicated than it could have been: The program interrupt handler in the kernel will try to crash the kernel: doing so, it will enable DAT. As the linear mapping is not created yet (asce=0), we run into an addressing exception while tring to walk non-existant DAT tables, resulting in a program exception loop. This allows for booting upstream Linux kernels compiled by clang-12. Most of these cases seem to be broken forever. Reported-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Tested-by: Nick Desaulniers <ndesaulniers@google.com> Tested-by: Guenter Roeck <linux@roeck-us.net> Cc: Guenter Roeck <linux@roeck-us.net> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Heiko Carstens <hca@linux.ibm.com> Signed-off-by: David Hildenbrand <david@redhat.com> Message-Id: <20210111163845.18148-4-david@redhat.com> Signed-off-by: Cornelia Huck <cohuck@redhat.com> |
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