mirror of
https://github.com/m-labs/artiq.git
synced 2024-12-26 03:38:25 +08:00
personality: update from rust/panic_unwind
This commit is contained in:
parent
bfddd8a30f
commit
31bf17563c
@ -15,7 +15,7 @@ use cslice::CSlice;
|
||||
use unwind as uw;
|
||||
use libc::{c_int, c_void};
|
||||
|
||||
use eh::dwarf::{self, EHAction};
|
||||
use eh::dwarf::{self, EHAction, EHContext};
|
||||
|
||||
type _Unwind_Stop_Fn = extern "C" fn(version: c_int,
|
||||
actions: uw::_Unwind_Action,
|
||||
@ -61,6 +61,9 @@ const UNWIND_DATA_REG: (i32, i32) = (0, 1); // RAX, RDX
|
||||
#[cfg(any(target_arch = "or1k"))]
|
||||
const UNWIND_DATA_REG: (i32, i32) = (3, 4); // R3, R4
|
||||
|
||||
#[cfg(any(target_arch = "riscv32"))]
|
||||
const UNWIND_DATA_REG: (i32, i32) = (10, 11); // X10, X11
|
||||
|
||||
#[export_name="__artiq_personality"]
|
||||
pub extern fn personality(version: c_int,
|
||||
actions: uw::_Unwind_Action,
|
||||
@ -74,13 +77,25 @@ pub extern fn personality(version: c_int,
|
||||
}
|
||||
|
||||
let lsda = uw::_Unwind_GetLanguageSpecificData(context) as *const u8;
|
||||
let ip = uw::_Unwind_GetIP(context) - 1;
|
||||
let func_start = uw::_Unwind_GetRegionStart(context);
|
||||
let mut ip_before_instr: c_int = 0;
|
||||
let ip = uw::_Unwind_GetIPInfo(context, &mut ip_before_instr);
|
||||
let eh_context = EHContext {
|
||||
// The return address points 1 byte past the call instruction,
|
||||
// which could be in the next IP range in LSDA range table.
|
||||
ip: if ip_before_instr != 0 { ip } else { ip - 1 },
|
||||
func_start: uw::_Unwind_GetRegionStart(context),
|
||||
get_text_start: &|| uw::_Unwind_GetTextRelBase(context),
|
||||
get_data_start: &|| uw::_Unwind_GetDataRelBase(context),
|
||||
};
|
||||
|
||||
let exception_info = &mut *(uw_exception as *mut ExceptionInfo);
|
||||
let exception = &exception_info.exception.unwrap();
|
||||
|
||||
let eh_action = dwarf::find_eh_action(lsda, func_start, ip, exception.name);
|
||||
let eh_action = match dwarf::find_eh_action(lsda, &eh_context) {
|
||||
Ok(action) => action,
|
||||
Err(_) => return uw::_URC_FATAL_PHASE1_ERROR,
|
||||
};
|
||||
|
||||
if actions as u32 & uw::_UA_SEARCH_PHASE as u32 != 0 {
|
||||
match eh_action {
|
||||
EHAction::None |
|
||||
|
||||
@ -1,51 +1,71 @@
|
||||
#![allow(non_upper_case_globals, dead_code)]
|
||||
//! Parsing of GCC-style Language-Specific Data Area (LSDA)
|
||||
//! For details see:
|
||||
//! * <https://refspecs.linuxfoundation.org/LSB_3.0.0/LSB-PDA/LSB-PDA/ehframechpt.html>
|
||||
//! * <https://itanium-cxx-abi.github.io/cxx-abi/exceptions.pdf>
|
||||
//! * <https://www.airs.com/blog/archives/460>
|
||||
//! * <https://www.airs.com/blog/archives/464>
|
||||
//!
|
||||
//! A reference implementation may be found in the GCC source tree
|
||||
//! (`<root>/libgcc/unwind-c.c` as of this writing).
|
||||
|
||||
use core::{ptr, mem};
|
||||
use cslice::CSlice;
|
||||
#![allow(non_upper_case_globals)]
|
||||
#![allow(unused)]
|
||||
|
||||
const DW_EH_PE_omit: u8 = 0xFF;
|
||||
const DW_EH_PE_absptr: u8 = 0x00;
|
||||
use core::mem;
|
||||
|
||||
const DW_EH_PE_uleb128: u8 = 0x01;
|
||||
const DW_EH_PE_udata2: u8 = 0x02;
|
||||
const DW_EH_PE_udata4: u8 = 0x03;
|
||||
const DW_EH_PE_udata8: u8 = 0x04;
|
||||
const DW_EH_PE_sleb128: u8 = 0x09;
|
||||
const DW_EH_PE_sdata2: u8 = 0x0A;
|
||||
const DW_EH_PE_sdata4: u8 = 0x0B;
|
||||
const DW_EH_PE_sdata8: u8 = 0x0C;
|
||||
pub const DW_EH_PE_omit: u8 = 0xFF;
|
||||
pub const DW_EH_PE_absptr: u8 = 0x00;
|
||||
|
||||
const DW_EH_PE_pcrel: u8 = 0x10;
|
||||
const DW_EH_PE_textrel: u8 = 0x20;
|
||||
const DW_EH_PE_datarel: u8 = 0x30;
|
||||
const DW_EH_PE_funcrel: u8 = 0x40;
|
||||
const DW_EH_PE_aligned: u8 = 0x50;
|
||||
pub const DW_EH_PE_uleb128: u8 = 0x01;
|
||||
pub const DW_EH_PE_udata2: u8 = 0x02;
|
||||
pub const DW_EH_PE_udata4: u8 = 0x03;
|
||||
pub const DW_EH_PE_udata8: u8 = 0x04;
|
||||
pub const DW_EH_PE_sleb128: u8 = 0x09;
|
||||
pub const DW_EH_PE_sdata2: u8 = 0x0A;
|
||||
pub const DW_EH_PE_sdata4: u8 = 0x0B;
|
||||
pub const DW_EH_PE_sdata8: u8 = 0x0C;
|
||||
|
||||
const DW_EH_PE_indirect: u8 = 0x80;
|
||||
pub const DW_EH_PE_pcrel: u8 = 0x10;
|
||||
pub const DW_EH_PE_textrel: u8 = 0x20;
|
||||
pub const DW_EH_PE_datarel: u8 = 0x30;
|
||||
pub const DW_EH_PE_funcrel: u8 = 0x40;
|
||||
pub const DW_EH_PE_aligned: u8 = 0x50;
|
||||
|
||||
#[derive(Clone)]
|
||||
struct DwarfReader {
|
||||
pub const DW_EH_PE_indirect: u8 = 0x80;
|
||||
|
||||
#[derive(Copy, Clone)]
|
||||
pub struct EHContext<'a> {
|
||||
pub ip: usize, // Current instruction pointer
|
||||
pub func_start: usize, // Address of the current function
|
||||
pub get_text_start: &'a dyn Fn() -> usize, // Get address of the code section
|
||||
pub get_data_start: &'a dyn Fn() -> usize, // Get address of the data section
|
||||
}
|
||||
|
||||
pub struct DwarfReader {
|
||||
pub ptr: *const u8,
|
||||
}
|
||||
|
||||
#[repr(C, packed)]
|
||||
struct Unaligned<T>(T);
|
||||
|
||||
impl DwarfReader {
|
||||
fn new(ptr: *const u8) -> DwarfReader {
|
||||
DwarfReader { ptr: ptr }
|
||||
pub fn new(ptr: *const u8) -> DwarfReader {
|
||||
DwarfReader { ptr }
|
||||
}
|
||||
|
||||
// DWARF streams are packed, so e.g. a u32 would not necessarily be aligned
|
||||
// DWARF streams are packed, so e.g., a u32 would not necessarily be aligned
|
||||
// on a 4-byte boundary. This may cause problems on platforms with strict
|
||||
// alignment requirements. By wrapping data in a "packed" struct, we are
|
||||
// telling the backend to generate "misalignment-safe" code.
|
||||
unsafe fn read<T: Copy>(&mut self) -> T {
|
||||
let result = ptr::read_unaligned(self.ptr as *const T);
|
||||
self.ptr = self.ptr.offset(mem::size_of::<T>() as isize);
|
||||
pub unsafe fn read<T: Copy>(&mut self) -> T {
|
||||
let Unaligned(result) = *(self.ptr as *const Unaligned<T>);
|
||||
self.ptr = self.ptr.add(mem::size_of::<T>());
|
||||
result
|
||||
}
|
||||
|
||||
// ULEB128 and SLEB128 encodings are defined in Section 7.6 - "Variable
|
||||
// Length Data".
|
||||
unsafe fn read_uleb128(&mut self) -> u64 {
|
||||
pub unsafe fn read_uleb128(&mut self) -> u64 {
|
||||
let mut shift: usize = 0;
|
||||
let mut result: u64 = 0;
|
||||
let mut byte: u8;
|
||||
@ -60,8 +80,8 @@ impl DwarfReader {
|
||||
result
|
||||
}
|
||||
|
||||
unsafe fn read_sleb128(&mut self) -> i64 {
|
||||
let mut shift: usize = 0;
|
||||
pub unsafe fn read_sleb128(&mut self) -> i64 {
|
||||
let mut shift: u32 = 0;
|
||||
let mut result: u64 = 0;
|
||||
let mut byte: u8;
|
||||
loop {
|
||||
@ -73,70 +93,61 @@ impl DwarfReader {
|
||||
}
|
||||
}
|
||||
// sign-extend
|
||||
if shift < 8 * mem::size_of::<u64>() && (byte & 0x40) != 0 {
|
||||
if shift < u64::BITS && (byte & 0x40) != 0 {
|
||||
result |= (!0 as u64) << shift;
|
||||
}
|
||||
result as i64
|
||||
}
|
||||
|
||||
unsafe fn read_encoded_pointer(&mut self, encoding: u8) -> usize {
|
||||
fn round_up(unrounded: usize, align: usize) -> usize {
|
||||
debug_assert!(align.is_power_of_two());
|
||||
(unrounded + align - 1) & !(align - 1)
|
||||
}
|
||||
|
||||
debug_assert!(encoding != DW_EH_PE_omit);
|
||||
|
||||
// DW_EH_PE_aligned implies it's an absolute pointer value
|
||||
if encoding == DW_EH_PE_aligned {
|
||||
self.ptr = round_up(self.ptr as usize, mem::size_of::<usize>()) as *const u8;
|
||||
return self.read::<usize>()
|
||||
}
|
||||
|
||||
let value_ptr = self.ptr;
|
||||
let mut result = match encoding & 0x0F {
|
||||
DW_EH_PE_absptr => self.read::<usize>(),
|
||||
DW_EH_PE_uleb128 => self.read_uleb128() as usize,
|
||||
DW_EH_PE_udata2 => self.read::<u16>() as usize,
|
||||
DW_EH_PE_udata4 => self.read::<u32>() as usize,
|
||||
DW_EH_PE_udata8 => self.read::<u64>() as usize,
|
||||
DW_EH_PE_sleb128 => self.read_sleb128() as usize,
|
||||
DW_EH_PE_sdata2 => self.read::<i16>() as usize,
|
||||
DW_EH_PE_sdata4 => self.read::<i32>() as usize,
|
||||
DW_EH_PE_sdata8 => self.read::<i64>() as usize,
|
||||
_ => panic!(),
|
||||
};
|
||||
|
||||
result += match encoding & 0x70 {
|
||||
DW_EH_PE_absptr => 0,
|
||||
// relative to address of the encoded value, despite the name
|
||||
DW_EH_PE_pcrel => value_ptr as usize,
|
||||
_ => panic!(),
|
||||
};
|
||||
|
||||
if encoding & DW_EH_PE_indirect != 0 {
|
||||
result = *(result as *const usize);
|
||||
}
|
||||
|
||||
result
|
||||
}
|
||||
}
|
||||
|
||||
fn encoding_size(encoding: u8) -> usize {
|
||||
unsafe fn read_encoded_pointer(
|
||||
reader: &mut DwarfReader,
|
||||
context: &EHContext<'_>,
|
||||
encoding: u8,
|
||||
) -> Result<usize, ()> {
|
||||
if encoding == DW_EH_PE_omit {
|
||||
return 0
|
||||
return Err(());
|
||||
}
|
||||
|
||||
match encoding & 0x0F {
|
||||
DW_EH_PE_absptr => mem::size_of::<usize>(),
|
||||
DW_EH_PE_udata2 => 2,
|
||||
DW_EH_PE_udata4 => 4,
|
||||
DW_EH_PE_udata8 => 8,
|
||||
DW_EH_PE_sdata2 => 2,
|
||||
DW_EH_PE_sdata4 => 4,
|
||||
DW_EH_PE_sdata8 => 8,
|
||||
_ => panic!()
|
||||
// DW_EH_PE_aligned implies it's an absolute pointer value
|
||||
if encoding == DW_EH_PE_aligned {
|
||||
reader.ptr = round_up(reader.ptr as usize, mem::size_of::<usize>())? as *const u8;
|
||||
return Ok(reader.read::<usize>());
|
||||
}
|
||||
|
||||
let mut result = match encoding & 0x0F {
|
||||
DW_EH_PE_absptr => reader.read::<usize>(),
|
||||
DW_EH_PE_uleb128 => reader.read_uleb128() as usize,
|
||||
DW_EH_PE_udata2 => reader.read::<u16>() as usize,
|
||||
DW_EH_PE_udata4 => reader.read::<u32>() as usize,
|
||||
DW_EH_PE_udata8 => reader.read::<u64>() as usize,
|
||||
DW_EH_PE_sleb128 => reader.read_sleb128() as usize,
|
||||
DW_EH_PE_sdata2 => reader.read::<i16>() as usize,
|
||||
DW_EH_PE_sdata4 => reader.read::<i32>() as usize,
|
||||
DW_EH_PE_sdata8 => reader.read::<i64>() as usize,
|
||||
_ => return Err(()),
|
||||
};
|
||||
|
||||
result += match encoding & 0x70 {
|
||||
DW_EH_PE_absptr => 0,
|
||||
// relative to address of the encoded value, despite the name
|
||||
DW_EH_PE_pcrel => reader.ptr as usize,
|
||||
DW_EH_PE_funcrel => {
|
||||
if context.func_start == 0 {
|
||||
return Err(());
|
||||
}
|
||||
context.func_start
|
||||
}
|
||||
DW_EH_PE_textrel => (*context.get_text_start)(),
|
||||
DW_EH_PE_datarel => (*context.get_data_start)(),
|
||||
_ => return Err(()),
|
||||
};
|
||||
|
||||
if encoding & DW_EH_PE_indirect != 0 {
|
||||
result = *(result as *const usize);
|
||||
}
|
||||
|
||||
Ok(result)
|
||||
}
|
||||
|
||||
pub enum EHAction {
|
||||
@ -146,98 +157,94 @@ pub enum EHAction {
|
||||
Terminate,
|
||||
}
|
||||
|
||||
pub unsafe fn find_eh_action(lsda: *const u8, func_start: usize, ip: usize,
|
||||
exn_name: CSlice<u8>) -> EHAction {
|
||||
pub const USING_SJLJ_EXCEPTIONS: bool = cfg!(all(target_os = "ios", target_arch = "arm"));
|
||||
|
||||
pub unsafe fn find_eh_action(lsda: *const u8, context: &EHContext<'_>) -> Result<EHAction, ()> {
|
||||
if lsda.is_null() {
|
||||
return EHAction::None
|
||||
return Ok(EHAction::None);
|
||||
}
|
||||
|
||||
let func_start = context.func_start;
|
||||
let mut reader = DwarfReader::new(lsda);
|
||||
|
||||
let start_encoding = reader.read::<u8>();
|
||||
// base address for landing pad offsets
|
||||
let lpad_base = if start_encoding != DW_EH_PE_omit {
|
||||
reader.read_encoded_pointer(start_encoding)
|
||||
read_encoded_pointer(&mut reader, context, start_encoding)?
|
||||
} else {
|
||||
func_start
|
||||
};
|
||||
|
||||
let ttype_encoding = reader.read::<u8>();
|
||||
let ttype_encoding_size = encoding_size(ttype_encoding) as isize;
|
||||
|
||||
let class_info;
|
||||
if ttype_encoding != DW_EH_PE_omit {
|
||||
let class_info_offset = reader.read_uleb128();
|
||||
class_info = reader.ptr.offset(class_info_offset as isize);
|
||||
} else {
|
||||
class_info = ptr::null();
|
||||
// Rust doesn't analyze exception types, so we don't care about the type table
|
||||
reader.read_uleb128();
|
||||
}
|
||||
assert!(!class_info.is_null());
|
||||
|
||||
let call_site_encoding = reader.read::<u8>();
|
||||
let call_site_table_length = reader.read_uleb128();
|
||||
let action_table = reader.ptr.offset(call_site_table_length as isize);
|
||||
let ip = context.ip;
|
||||
|
||||
while reader.ptr < action_table {
|
||||
let cs_start = reader.read_encoded_pointer(call_site_encoding);
|
||||
let cs_len = reader.read_encoded_pointer(call_site_encoding);
|
||||
let cs_lpad = reader.read_encoded_pointer(call_site_encoding);
|
||||
let cs_action = reader.read_uleb128();
|
||||
|
||||
if ip < func_start + cs_start {
|
||||
if !USING_SJLJ_EXCEPTIONS {
|
||||
while reader.ptr < action_table {
|
||||
let cs_start = read_encoded_pointer(&mut reader, context, call_site_encoding)?;
|
||||
let cs_len = read_encoded_pointer(&mut reader, context, call_site_encoding)?;
|
||||
let cs_lpad = read_encoded_pointer(&mut reader, context, call_site_encoding)?;
|
||||
let cs_action = reader.read_uleb128();
|
||||
// Callsite table is sorted by cs_start, so if we've passed the ip, we
|
||||
// may stop searching.
|
||||
break
|
||||
if ip < func_start + cs_start {
|
||||
break;
|
||||
}
|
||||
if ip < func_start + cs_start + cs_len {
|
||||
if cs_lpad == 0 {
|
||||
return Ok(EHAction::None);
|
||||
} else {
|
||||
let lpad = lpad_base + cs_lpad;
|
||||
return Ok(interpret_cs_action(cs_action, lpad));
|
||||
}
|
||||
}
|
||||
}
|
||||
if ip > func_start + cs_start + cs_len {
|
||||
continue
|
||||
// Ip is not present in the table. This should not happen... but it does: issue #35011.
|
||||
// So rather than returning EHAction::Terminate, we do this.
|
||||
Ok(EHAction::None)
|
||||
} else {
|
||||
// SjLj version:
|
||||
// The "IP" is an index into the call-site table, with two exceptions:
|
||||
// -1 means 'no-action', and 0 means 'terminate'.
|
||||
match ip as isize {
|
||||
-1 => return Ok(EHAction::None),
|
||||
0 => return Ok(EHAction::Terminate),
|
||||
_ => (),
|
||||
}
|
||||
|
||||
if cs_lpad == 0 {
|
||||
return EHAction::None
|
||||
}
|
||||
|
||||
let lpad = lpad_base + cs_lpad;
|
||||
if cs_action == 0 {
|
||||
return EHAction::Cleanup(lpad)
|
||||
}
|
||||
|
||||
let action_entry = action_table.offset((cs_action - 1) as isize);
|
||||
let mut action_reader = DwarfReader::new(action_entry);
|
||||
let mut idx = ip;
|
||||
loop {
|
||||
let type_info_offset = action_reader.read_sleb128() as isize;
|
||||
let action_offset = action_reader.clone().read_sleb128() as isize;
|
||||
assert!(type_info_offset >= 0);
|
||||
|
||||
if type_info_offset > 0 {
|
||||
let type_info_ptr_ptr = class_info.offset(-type_info_offset * ttype_encoding_size);
|
||||
let type_info_ptr = DwarfReader::new(type_info_ptr_ptr)
|
||||
.read_encoded_pointer(ttype_encoding);
|
||||
let type_info = *(type_info_ptr as *const CSlice<u8>);
|
||||
|
||||
if type_info.as_ref() == exn_name.as_ref() {
|
||||
return EHAction::Catch(lpad)
|
||||
}
|
||||
|
||||
if type_info.len() == 0 {
|
||||
// This is a catch-all clause. We don't compare type_info_ptr with null here
|
||||
// because, in PIC mode, the OR1K LLVM backend emits a literal zero
|
||||
// encoded with DW_EH_PE_pcrel, which of course doesn't result in
|
||||
// a proper null pointer.
|
||||
return EHAction::Catch(lpad)
|
||||
}
|
||||
}
|
||||
|
||||
if action_offset == 0 {
|
||||
break
|
||||
} else {
|
||||
action_reader.ptr = action_reader.ptr.offset(action_offset)
|
||||
let cs_lpad = reader.read_uleb128();
|
||||
let cs_action = reader.read_uleb128();
|
||||
idx -= 1;
|
||||
if idx == 0 {
|
||||
// Can never have null landing pad for sjlj -- that would have
|
||||
// been indicated by a -1 call site index.
|
||||
let lpad = (cs_lpad + 1) as usize;
|
||||
return Ok(interpret_cs_action(cs_action, lpad));
|
||||
}
|
||||
}
|
||||
|
||||
return EHAction::None
|
||||
}
|
||||
|
||||
// the function has a personality but no landing pads; this is fine
|
||||
EHAction::None
|
||||
}
|
||||
|
||||
fn interpret_cs_action(cs_action: u64, lpad: usize) -> EHAction {
|
||||
if cs_action == 0 {
|
||||
// If cs_action is 0 then this is a cleanup (Drop::drop). We run these
|
||||
// for both Rust panics and foreign exceptions.
|
||||
EHAction::Cleanup(lpad)
|
||||
} else {
|
||||
// Stop unwinding Rust panics at catch_unwind.
|
||||
EHAction::Catch(lpad)
|
||||
}
|
||||
}
|
||||
|
||||
#[inline]
|
||||
fn round_up(unrounded: usize, align: usize) -> Result<usize, ()> {
|
||||
if align.is_power_of_two() { Ok((unrounded + align - 1) & !(align - 1)) } else { Err(()) }
|
||||
}
|
||||
|
||||
@ -20,7 +20,7 @@ use unwind as uw;
|
||||
use libc::{c_int, uintptr_t};
|
||||
use cslice::AsCSlice;
|
||||
|
||||
use dwarf::{self, EHAction};
|
||||
use dwarf::{self, EHAction, EHContext};
|
||||
|
||||
// Register ids were lifted from LLVM's TargetLowering::getExceptionPointerRegister()
|
||||
// and TargetLowering::getExceptionSelectorRegister() for each architecture,
|
||||
@ -37,6 +37,9 @@ const UNWIND_DATA_REG: (i32, i32) = (0, 1); // RAX, RDX
|
||||
#[cfg(any(target_arch = "or1k"))]
|
||||
const UNWIND_DATA_REG: (i32, i32) = (3, 4); // R3, R4
|
||||
|
||||
#[cfg(any(target_arch = "riscv32"))]
|
||||
const UNWIND_DATA_REG: (i32, i32) = (10, 11); // X10, X11
|
||||
|
||||
// The following code is based on GCC's C and C++ personality routines. For reference, see:
|
||||
// https://github.com/gcc-mirror/gcc/blob/master/libstdc++-v3/libsupc++/eh_personality.cc
|
||||
// https://github.com/gcc-mirror/gcc/blob/trunk/libgcc/unwind-c.c
|
||||
@ -78,11 +81,17 @@ unsafe extern "C" fn rust_eh_personality(version: c_int,
|
||||
}
|
||||
}
|
||||
|
||||
unsafe fn find_eh_action(context: *mut uw::_Unwind_Context)
|
||||
-> Result<EHAction, ()>
|
||||
{
|
||||
unsafe fn find_eh_action(context: *mut uw::_Unwind_Context) -> Result<EHAction, ()> {
|
||||
let lsda = uw::_Unwind_GetLanguageSpecificData(context) as *const u8;
|
||||
let func = uw::_Unwind_GetRegionStart(context);
|
||||
let ip = uw::_Unwind_GetIP(context);
|
||||
Ok(dwarf::find_eh_action(lsda, func, ip, [].as_c_slice()))
|
||||
let mut ip_before_instr: c_int = 0;
|
||||
let ip = uw::_Unwind_GetIPInfo(context, &mut ip_before_instr);
|
||||
let eh_context = EHContext {
|
||||
// The return address points 1 byte past the call instruction,
|
||||
// which could be in the next IP range in LSDA range table.
|
||||
ip: if ip_before_instr != 0 { ip } else { ip - 1 },
|
||||
func_start: uw::_Unwind_GetRegionStart(context),
|
||||
get_text_start: &|| uw::_Unwind_GetTextRelBase(context),
|
||||
get_data_start: &|| uw::_Unwind_GetDataRelBase(context),
|
||||
};
|
||||
dwarf::find_eh_action(lsda, &eh_context)
|
||||
}
|
||||
|
||||
Loading…
Reference in New Issue
Block a user