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keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: <5005ead1-b7e2-4edc-8359-c2a9a89e5b4d@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-purgate-ID: tlsNG-c1860d/1787049045-CED4087B-7CBF197B/0/0 X-purgate-type: clean X-purgate-size: 5115 On 18.08.2026 11:40, Oleksii Kurochko wrote: > On 8/18/26 11:26 AM, Jan Beulich wrote: >> On 18.08.2026 11:14, Oleksii Kurochko wrote: >>> On 8/18/26 9:56 AM, Jan Beulich wrote: >>>> On 17.08.2026 13:33, Oleksii Kurochko wrote: >>>>> On 8/12/26 4:37 PM, Jan Beulich wrote: >>>>>> On 20.07.2026 18:02, Oleksii Kurochko wrote: >>>>>>> @@ -60,6 +68,40 @@ static void ex_handler_fixup(const struct exception_table_entry *ex, >>>>>>> regs->sepc = ex_fixup(ex); >>>>>>> } >>>>>>> >>>>>>> +static inline unsigned long regs_get_gpr(struct cpu_user_regs *regs, >>>>>>> + unsigned int offset) >>>>>>> +{ >>>>>>> + /* >>>>>>> + * The GPR number -> offset arithmetic below relies on x0..x31 being >>>>>>> + * laid out at the start of struct cpu_user_regs in architectural >>>>>>> + * order. >>>>>>> + */ >>>>>>> + BUILD_BUG_ON(offsetof(struct cpu_user_regs, ra) != >>>>>>> + sizeof(unsigned long)); >>>>>>> + BUILD_BUG_ON(offsetof(struct cpu_user_regs, t6) != >>>>>>> + 31 * sizeof(unsigned long)); >>>>>>> + >>>>>>> + if ( unlikely(!offset || (offset > MAX_REG_OFFSET)) ) >>>>>>> + return 0; >>>>>> >>>>>> And an offset not divisible by sizeof(unsigned long) is okay? >>>>> >>>>> No, it isn't okay. I will apply your comment ... >>>>> >>>>>> >>>>>> Returning 0 as error indicator also feels fragile. >>>>> >>>>> With what I suggested below returning could be just dropped. >>>>> >>>>>> >>>>>>> + return *(unsigned long *)((unsigned long)regs + offset); >>>>>>> +} >>>>>>> + >>>>>>> +static void ex_handler_trap_info(const struct exception_table_entry *ex, >>>>>>> + struct cpu_user_regs *regs) >>>>>>> +{ >>>>>>> + struct trap_info *trap_info = >>>>>>> + (struct trap_info *)regs_get_gpr(regs, ex->data * sizeof(unsigned long)); >>>>>> >>>>>> Related to the earlier comment: Simply pass just ex->data here, leaving the >>>>>> multiplication to regs_get_gpr()? >>>>> >>>>> ... It would be better to move the multiplication inside regs_get_gpr(). >>>>> >>>>> Your comment made me think about whether the multiplication is needed at >>>>> all (regardless of where it is done). In other words, ex->data contains >>>>> the register number, so we could just write: >>>>> >>>>> static unsigned long regs_get_gpr(const struct cpu_user_regs *regs, >>>>> unsigned int num) >>>>> { >>>>> /* >>>>> * The GPR number -> offset arithmetic below relies on x0..x31 being >>>>> * laid out at the start of struct cpu_user_regs in architectural >>>>> order. >>>>> */ >>>>> BUILD_BUG_ON(offsetof(struct cpu_user_regs, ra) != sizeof(unsigned >>>>> long)); >>>>> BUILD_BUG_ON(offsetof(struct cpu_user_regs, t6) != 31 * >>>>> sizeof(unsigned long)); >>>>> >>>>> ASSERT(num && (num < 32)); >>>>> >>>>> return ((const unsigned long *)regs)[num]; >>>>> } >>>>> >>>>> Probably, we want to consider this function out of context (for now >>>>> context is that we use it to recieve a pointer to trap_info which can't >>>>> be obviously stored in x0 as it should be always hardwired zero). In >>>>> that case, there is no need to check that num is 0. >>>>> >>>>> So, it probably makes sense to just have: >>>>> ASSERT(num < 32); >>>>> >>>>> ASSERT() is fine here as I don't think that compiler will use incorrect >>>>> number during register allocation. >>>> >>>> I agree. >>>> >>>> However, the x0 aspect is still odd. Why again is it that struct cpu_user_regs >>>> has a field for it, when the register value is always 0? >>> >>> zero field isn't there to hold a value, it's there so the first 32 slots >>> form an x0..x31 array indexed by GPR number. It is useful for SET_RD() >>> implementation, for example. >> >> But SET_RD() will need to avoid touching .zero anyway. Why waste the space, >> when something useful can be put there? > > For SET_RD() agree, it doesn't make sense. Bad example. But it could be > somehow a "protection" to not clobber something useful if SET_RD > arguments won't handled correctly. > > SET_RD() is only half of it. The read accessors matter more: sd x0, > 0(a0) to an MMIO address is the normal way a guest writes 0 to a device > register, and emulate_store() fetches the operand with GET_RS2(), which > is a plain index by register number. Oh, wow, how fragile. Without a bright comment in struct cpu_user_regs, one should be permitted to move fields around or insert new ones at arbitrary positions. That comment would then also help clarify why "zero" is there as a field. > If something useful lived at offset > 0, that store would hand the device that value instead of zero. So > whatever we put there would have to survive being read as a source > operand and being clobbered by SET_RD(), which means nothing can go there. But you can't use it as (reliable zero) source when you allow SET_RD() to clobber it. Jan