std: move personality implementation out of PAL

3 files changed, 349 insertions, 0 deletions

diff --git a/library/std/src/sys/personality/dwarf/eh.rs b/library/std/src/sys/personality/dwarf/eh.rs
new file mode 100644
index 00000000000..a78084de0fa
--- /dev/null
+++ b/library/std/src/sys/personality/dwarf/eh.rs
@@ -0,0 +1,257 @@
+//! 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://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/dwarfext.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).
+
+#![allow(non_upper_case_globals)]
+#![allow(unused)]
+
+use super::DwarfReader;
+use core::mem;
+use core::ptr;
+
+pub const DW_EH_PE_omit: u8 = 0xFF;
+pub const DW_EH_PE_absptr: u8 = 0x00;
+
+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;
+
+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;
+
+pub const DW_EH_PE_indirect: u8 = 0x80;
+
+#[derive(Copy, Clone)]
+pub struct EHContext<'a> {
+    pub ip: *const u8,                             // Current instruction pointer
+    pub func_start: *const u8,                     // Pointer to the current function
+    pub get_text_start: &'a dyn Fn() -> *const u8, // Get pointer to the code section
+    pub get_data_start: &'a dyn Fn() -> *const u8, // Get pointer to the data section
+}
+
+/// Landing pad.
+type LPad = *const u8;
+pub enum EHAction {
+    None,
+    Cleanup(LPad),
+    Catch(LPad),
+    Filter(LPad),
+    Terminate,
+}
+
+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 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 {
+        read_encoded_pointer(&mut reader, context, start_encoding)?
+    } else {
+        func_start
+    };
+
+    let ttype_encoding = reader.read::<u8>();
+    if ttype_encoding != DW_EH_PE_omit {
+        // Rust doesn't analyze exception types, so we don't care about the type table
+        reader.read_uleb128();
+    }
+
+    let call_site_encoding = reader.read::<u8>();
+    let call_site_table_length = reader.read_uleb128();
+    let action_table = reader.ptr.add(call_site_table_length as usize);
+    let ip = context.ip;
+
+    if !USING_SJLJ_EXCEPTIONS {
+        // read the callsite table
+        while reader.ptr < action_table {
+            // these are offsets rather than pointers;
+            let cs_start = read_encoded_offset(&mut reader, call_site_encoding)?;
+            let cs_len = read_encoded_offset(&mut reader, call_site_encoding)?;
+            let cs_lpad = read_encoded_offset(&mut reader, call_site_encoding)?;
+            let cs_action_entry = reader.read_uleb128();
+            // Callsite table is sorted by cs_start, so if we've passed the ip, we
+            // may stop searching.
+            if ip < func_start.wrapping_add(cs_start) {
+                break;
+            }
+            if ip < func_start.wrapping_add(cs_start + cs_len) {
+                if cs_lpad == 0 {
+                    return Ok(EHAction::None);
+                } else {
+                    let lpad = lpad_base.wrapping_add(cs_lpad);
+                    return Ok(interpret_cs_action(action_table, cs_action_entry, lpad));
+                }
+            }
+        }
+        // Ip is not present in the table. This indicates a nounwind call.
+        Ok(EHAction::Terminate)
+    } 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.addr() as isize {
+            -1 => return Ok(EHAction::None),
+            0 => return Ok(EHAction::Terminate),
+            _ => (),
+        }
+        let mut idx = ip.addr();
+        loop {
+            let cs_lpad = reader.read_uleb128();
+            let cs_action_entry = 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.
+                // FIXME(strict provenance)
+                let lpad = ptr::from_exposed_addr((cs_lpad + 1) as usize);
+                return Ok(interpret_cs_action(action_table, cs_action_entry, lpad));
+            }
+        }
+    }
+}
+
+unsafe fn interpret_cs_action(
+    action_table: *const u8,
+    cs_action_entry: u64,
+    lpad: LPad,
+) -> EHAction {
+    if cs_action_entry == 0 {
+        // If cs_action_entry is 0 then this is a cleanup (Drop::drop). We run these
+        // for both Rust panics and foreign exceptions.
+        EHAction::Cleanup(lpad)
+    } else {
+        // If lpad != 0 and cs_action_entry != 0, we have to check ttype_index.
+        // If ttype_index == 0 under the condition, we take cleanup action.
+        let action_record = action_table.offset(cs_action_entry as isize - 1);
+        let mut action_reader = DwarfReader::new(action_record);
+        let ttype_index = action_reader.read_sleb128();
+        if ttype_index == 0 {
+            EHAction::Cleanup(lpad)
+        } else if ttype_index > 0 {
+            // Stop unwinding Rust panics at catch_unwind.
+            EHAction::Catch(lpad)
+        } else {
+            EHAction::Filter(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(()) }
+}
+
+/// Read a offset (`usize`) from `reader` whose encoding is described by `encoding`.
+///
+/// `encoding` must be a [DWARF Exception Header Encoding as described by the LSB spec][LSB-dwarf-ext].
+/// In addition the upper ("application") part must be zero.
+///
+/// # Errors
+/// Returns `Err` if `encoding`
+/// * is not a valid DWARF Exception Header Encoding,
+/// * is `DW_EH_PE_omit`, or
+/// * has a non-zero application part.
+///
+/// [LSB-dwarf-ext]: https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/dwarfext.html
+unsafe fn read_encoded_offset(reader: &mut DwarfReader, encoding: u8) -> Result<usize, ()> {
+    if encoding == DW_EH_PE_omit || encoding & 0xF0 != 0 {
+        return Err(());
+    }
+    let result = match encoding & 0x0F {
+        // despite the name, LLVM also uses absptr for offsets instead of pointers
+        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(()),
+    };
+    Ok(result)
+}
+
+/// Read a pointer from `reader` whose encoding is described by `encoding`.
+///
+/// `encoding` must be a [DWARF Exception Header Encoding as described by the LSB spec][LSB-dwarf-ext].
+///
+/// # Errors
+/// Returns `Err` if `encoding`
+/// * is not a valid DWARF Exception Header Encoding,
+/// * is `DW_EH_PE_omit`, or
+/// * combines `DW_EH_PE_absptr` or `DW_EH_PE_aligned` application part with an integer encoding
+///   (not `DW_EH_PE_absptr`) in the value format part.
+///
+/// [LSB-dwarf-ext]: https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/dwarfext.html
+unsafe fn read_encoded_pointer(
+    reader: &mut DwarfReader,
+    context: &EHContext<'_>,
+    encoding: u8,
+) -> Result<*const u8, ()> {
+    if encoding == DW_EH_PE_omit {
+        return Err(());
+    }
+
+    let base_ptr = match encoding & 0x70 {
+        DW_EH_PE_absptr => core::ptr::null(),
+        // relative to address of the encoded value, despite the name
+        DW_EH_PE_pcrel => reader.ptr,
+        DW_EH_PE_funcrel => {
+            if context.func_start.is_null() {
+                return Err(());
+            }
+            context.func_start
+        }
+        DW_EH_PE_textrel => (*context.get_text_start)(),
+        DW_EH_PE_datarel => (*context.get_data_start)(),
+        // aligned means the value is aligned to the size of a pointer
+        DW_EH_PE_aligned => {
+            reader.ptr =
+                reader.ptr.with_addr(round_up(reader.ptr.addr(), mem::size_of::<*const u8>())?);
+            core::ptr::null()
+        }
+        _ => return Err(()),
+    };
+
+    let mut ptr = if base_ptr.is_null() {
+        // any value encoding other than absptr would be nonsensical here;
+        // there would be no source of pointer provenance
+        if encoding & 0x0F != DW_EH_PE_absptr {
+            return Err(());
+        }
+        reader.read::<*const u8>()
+    } else {
+        let offset = read_encoded_offset(reader, encoding & 0x0F)?;
+        base_ptr.wrapping_add(offset)
+    };
+
+    if encoding & DW_EH_PE_indirect != 0 {
+        ptr = *(ptr.cast::<*const u8>());
+    }
+
+    Ok(ptr)
+}
diff --git a/library/std/src/sys/personality/dwarf/mod.rs b/library/std/src/sys/personality/dwarf/mod.rs
new file mode 100644
index 00000000000..652fbe95a14
--- /dev/null
+++ b/library/std/src/sys/personality/dwarf/mod.rs
@@ -0,0 +1,73 @@
+//! Utilities for parsing DWARF-encoded data streams.
+//! See <http://www.dwarfstd.org>,
+//! DWARF-4 standard, Section 7 - "Data Representation"
+
+// This module is used only by x86_64-pc-windows-gnu for now, but we
+// are compiling it everywhere to avoid regressions.
+#![allow(unused)]
+
+#[cfg(test)]
+mod tests;
+
+pub mod eh;
+
+use core::mem;
+
+pub struct DwarfReader {
+    pub ptr: *const u8,
+}
+
+#[repr(C, packed)]
+struct Unaligned<T>(T);
+
+impl DwarfReader {
+    pub fn new(ptr: *const u8) -> DwarfReader {
+        DwarfReader { ptr }
+    }
+
+    // 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.
+    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".
+    pub unsafe fn read_uleb128(&mut self) -> u64 {
+        let mut shift: usize = 0;
+        let mut result: u64 = 0;
+        let mut byte: u8;
+        loop {
+            byte = self.read::<u8>();
+            result |= ((byte & 0x7F) as u64) << shift;
+            shift += 7;
+            if byte & 0x80 == 0 {
+                break;
+            }
+        }
+        result
+    }
+
+    pub unsafe fn read_sleb128(&mut self) -> i64 {
+        let mut shift: u32 = 0;
+        let mut result: u64 = 0;
+        let mut byte: u8;
+        loop {
+            byte = self.read::<u8>();
+            result |= ((byte & 0x7F) as u64) << shift;
+            shift += 7;
+            if byte & 0x80 == 0 {
+                break;
+            }
+        }
+        // sign-extend
+        if shift < u64::BITS && (byte & 0x40) != 0 {
+            result |= (!0 as u64) << shift;
+        }
+        result as i64
+    }
+}
diff --git a/library/std/src/sys/personality/dwarf/tests.rs b/library/std/src/sys/personality/dwarf/tests.rs
new file mode 100644
index 00000000000..1644f37083a
--- /dev/null
+++ b/library/std/src/sys/personality/dwarf/tests.rs
@@ -0,0 +1,19 @@
+use super::*;
+
+#[test]
+fn dwarf_reader() {
+    let encoded: &[u8] = &[1, 2, 3, 4, 5, 6, 7, 0xE5, 0x8E, 0x26, 0x9B, 0xF1, 0x59, 0xFF, 0xFF];
+
+    let mut reader = DwarfReader::new(encoded.as_ptr());
+
+    unsafe {
+        assert!(reader.read::<u8>() == u8::to_be(1u8));
+        assert!(reader.read::<u16>() == u16::to_be(0x0203));
+        assert!(reader.read::<u32>() == u32::to_be(0x04050607));
+
+        assert!(reader.read_uleb128() == 624485);
+        assert!(reader.read_sleb128() == -624485);
+
+        assert!(reader.read::<i8>() == i8::to_be(-1));
+    }
+}