Method push

crates/cranelift/src/obj.rs:267–369

Pushes the unwind information for a function into this builder. The function being described must be located at `function_offset` within the text section itself, and the function's size is specified by `function_len`. The `info` should come from Cranelift. and is handled here depending on its flavor.

(&mut self, function_offset: u64, function_len: u64, info: &'a UnwindInfo)

    /// The `info` should come from Cranelift. and is handled here depending on
    /// its flavor.
    fn push(&mut self, function_offset: u64, function_len: u64, info: &'a UnwindInfo) {
        match info {
            // Windows unwind information is stored in two locations:
            //
            // * First is the actual unwinding information which is stored
            //   in the `.xdata` section. This is where `info`'s emitted
            //   information will go into.
            // * Second are pointers to connect all this unwind information,
            //   stored in the `.pdata` section. The `.pdata` section is an
            //   array of `RUNTIME_FUNCTION` structures.
            //
            // Due to how these will be loaded at runtime the `.pdata` isn't
            // actually assembled byte-wise here. Instead that's deferred to
            // happen later during `write_windows_unwind_info` which will apply
            // a further offset to `unwind_address`.
            //
            // FIXME: in theory we could "intern" the `unwind_info` value
            // here within the `.xdata` section. Most of our unwind
            // information for functions is probably pretty similar in which
            // case the `.xdata` could be quite small and `.pdata` could
            // have multiple functions point to the same unwinding
            // information.
            UnwindInfo::WindowsX64(info) => {
                let unwind_size = info.emit_size();
                let mut unwind_info = vec![0; unwind_size];
                info.emit(&mut unwind_info);

                // `.xdata` entries are always 4-byte aligned
                while self.windows_xdata.len() % 4 != 0 {
                    self.windows_xdata.push(0x00);
                }
                let unwind_address = self.windows_xdata.len();
                self.windows_xdata.extend_from_slice(&unwind_info);

                // Record a `RUNTIME_FUNCTION` which this will point to.
                self.windows_pdata.push(RUNTIME_FUNCTION {
                    begin: u32::try_from(function_offset).unwrap(),
                    end: u32::try_from(function_offset + function_len).unwrap(),
                    unwind_address: u32::try_from(unwind_address).unwrap(),
                });
            }

            // See https://learn.microsoft.com/en-us/cpp/build/arm64-exception-handling
            UnwindInfo::WindowsArm64(info) => {
                let code_words = info.code_words();
                let mut unwind_codes = vec![0; (code_words * 4) as usize];
                info.emit(&mut unwind_codes);

                // `.xdata` entries are always 4-byte aligned
                while self.windows_xdata.len() % 4 != 0 {
                    self.windows_xdata.push(0x00);
                }

                // First word:
                // 0-17:    Function Length
                // 18-19:   Version (must be 0)
                // 20:      X bit (is exception data present?)
                // 21:      E bit (has single packed epilogue?)