[Bug 1858461] Re: Please refactor linux-user/mips/cpu_loop.c

[puchuu <1858461@bugs.launchpad.net>]

Please do not use previous workaround in prod, it is bad, just proof of
concept.

It looks like nobody is maintaining syscall list. It is not possible to
trust it.

We have "arch/mips/kernel/syscalls/syscall_o32.tbl", we need to create
generator. Generator should provide maximum possible number of arguments
for syscall. For example:

> sync_file_range  sys_sync_file_range  sys32_sync_file_range

"sys_sync_file_range" has 4 arguments, "sys32_sync_file_range" - 7
arguments. Maximum value - 7 should be stored inside our table.

The problem is that some syscalls in kernel code is prefixed by
SYSCALL_DEFINE{N} or COMPAT_SYSCALL_DEFINE{N}. but some (like
"sys_sync_file_range" and "sys32_sync_file_range") are not prefixed.

So I think we may have a generator that provides "WAT?" if it don't know
the arguments count and require to update value manualy.

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https://bugs.launchpad.net/bugs/1858461

Title:
  Please refactor linux-user/mips/cpu_loop.c

Status in QEMU:
  New

Bug description:
  Hello. I am working with qemu on test images. I've added a new syscall
  (436) to qemu but received ENOSYS from mips application.

  Please open "linux-user/mips/cpu_loop.c". I've added at the end of
  "mips_syscall_args" the following:

  ```
  MIPS_SYS(sys_getdents64_x32, 3)
  ```

  But

  ```
  syscall_num = env->active_tc.gpr[2] - 4000;
  if (syscall_num >= sizeof(mips_syscall_args)) {
    ret = -TARGET_ENOSYS;
  ```

  returns -TARGET_ENOSYS

  We can see that "linux-user/mips/cpu_loop.c" differs a lot from
  "linux-user/arm/cpu_loop.c". Arm has it's own "ARM_NR_BASE" and etc.

  Can you please refactor mips cpu loop in the same way as arm? Thank
  you.

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