The kernel doesn't support msg_iovlens != 1 yet and nothing passes
an amount != 1, but if anyone ever adds support for this they won't
have to worry about ue at least.
When SO_TIMESTAMP is set as an option on a SOCK_DGRAM socket, then
recvmsg() will return a SCM_TIMESTAMP control message that
contains a struct timeval with the system time that was current
when the socket was received.
The implementation only supports a single iovec for now.
Some might say having more than one iovec is the main point of
recvmsg() and sendmsg(), but I'm interested in the control message
bits.
* Pass the correct source address for copying tine addr_length.
Previously, this was broken when addr_length was non-nullptr.
* Copy min(sizeof(address), address_length) bytes into address,
instead of sizeof(address), which might be larger than the
user buffer.
* Use sockaddr_storage instead of sockaddr_un. In practice they're
both the same size, but this is what sockaddr_storage is for.
With this (in particular, the first fix), `ue /bin/ntpquery`
actually gets past the recvfrom() call :^)
With this, `ue /bin/ntpquery` can be used to test sendto() and
recvfrom() in ue. (It eventually hits an unimplemented FILD_RM64,
but not before doing emulated network i/o and printing response
details.)
Since the CPU already does almost all necessary validation steps
for us, we don't really need to attempt to do this. Doing it
ourselves doesn't really work very reliably, because we'd have to
account for other processors modifying virtual memory, and we'd
have to account for e.g. pages not being able to be allocated
due to insufficient resources.
So change the copy_to/from_user (and associated helper functions)
to use the new safe_memcpy, which will return whether it succeeded
or not. The only manual validation step needed (which the CPU
can't perform for us) is making sure the pointers provided by user
mode aren't pointing to kernel mappings.
To make it easier to read/write from/to either kernel or user mode
data add the UserOrKernelBuffer helper class, which will internally
either use copy_from/to_user or directly memcpy, or pass the data
through directly using a temporary buffer on the stack.
Last but not least we need to keep syscall params trivial as we
need to copy them from/to user mode using copy_from/to_user.
From a layering perspective, it's maybe a bit surprising that the
X86::SymbolProvider implementation also lives in LibX86, but since
everything depends on LibELF via LibC, and since all current
LibX86-based disassemblers want to use ELFSymbolProvider, it makes
some amount of sense to put it there.
The SI prefixes "k", "M", "G" mean "10^3", "10^6", "10^9".
The IEC prefixes "Ki", "Mi", "Gi" mean "2^10", "2^20", "2^30".
Let's use the correct name, at least in code.
Only changes the name of the constants, no other behavior change.
This is racy in userspace and non-racy in kernelspace so let's keep
it in kernelspace.
The behavior change where CLOEXEC is preserved when dup2() is called
with (old_fd == new_fd) was good though, let's keep that.
This enables a nice warning in case a function becomes dead code. Also, in case
of signal_trampoline_dummy, marking it external (non-static) prevents it from
being 'optimized away', which would lead to surprising and weird linker errors.
When compiling with "-Os", GCC produces the following pattern for
atomic decrement (which is used by our RefCounted template):
or eax, -1
lock xadd [destination], eax
Since or-ing with -1 will always produce the same output (-1), we can
mark the result of these operations as initialized. This stops us from
complaining about false positives when running the shell in UE. :^)
The emulator will now register signal handlers for all possible signals
and act as a translation layer between the kernel and the emulated
process.
To get an accurate simulation of signal handling, we duplicate the same
trampoline mechanism used by the kernel's signal delivery system, and
also use the "sigreturn" syscall to return from a signal handler.
Signal masking is not fully implemented yet, but this is pretty cool!
We don't have to be clever at all to figure out which MmapRegions are
malloc blocks, we can just mark the containing region as such when
the emulated process performs a malloc! :^)
Some of the remaining instructions have different behavior for
register and non-register ops. Since we already have the
two-level flags tables, model this by setting all handlers in
the two-level table to the register op handler, while the
first-level flags table stores the action for the non-reg handler.
Some of these don't just use the REG bits of the mod/rm byte
as slashes, but also the R/M bits to have up to 9 different
instructions per opcode/slash combination (1 opcode requires
that MOD is != 11, the other 8 have MODE == 11).
This is done by making the slashes table two levels deep for
these cases.
Some of this is cosmetic (e.g "FST st0" has no effect already,
but its bit pattern gets disassembled as "FNOP"), but for
most uses it isn't.
FSTENV and FSTCW have an extraordinary 0x9b prefix. This is
not yet handled in this patch.
This virtual syscall works by exec'ing the UserspaceEmulator itself,
with the emulated program's provided arguments as the arguments to the
new UserspaceEmulator instance.
This means that we "follow" exec'ed programs and emulate them as well.
In the future we might want to make this an opt-in (or opt-out, idk)
behavior, but for now it's what we do.
This is really quite cool, I think! :^)
