wasmtime_environ/obj.rs
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179
//! Utilities for working with object files that operate as Wasmtime's
//! serialization and intermediate format for compiled modules.
/// Filler for the `os_abi` field of the ELF header.
///
/// This is just a constant that seems reasonable in the sense it's unlikely to
/// clash with others.
pub const ELFOSABI_WASMTIME: u8 = 200;
/// Flag for the `e_flags` field in the ELF header indicating a compiled
/// module.
pub const EF_WASMTIME_MODULE: u32 = 1 << 0;
/// Flag for the `e_flags` field in the ELF header indicating a compiled
/// component.
pub const EF_WASMTIME_COMPONENT: u32 = 1 << 1;
/// Flag for the `sh_flags` field in the ELF text section that indicates that
/// the text section does not itself need to be executable. This is used for the
/// Pulley target, for example, to indicate that it does not need to be made
/// natively executable as it does not contain actual native code.
pub const SH_WASMTIME_NOT_EXECUTED: u64 = 1 << 0;
/// A custom Wasmtime-specific section of our compilation image which stores
/// mapping data from offsets in the image to offset in the original wasm
/// binary.
///
/// This section has a custom binary encoding. Currently its encoding is:
///
/// * The section starts with a 32-bit little-endian integer. This integer is
/// how many entries are in the following two arrays.
/// * Next is an array with the previous count number of 32-bit little-endian
/// integers. This array is a sorted list of relative offsets within the text
/// section. This is intended to be a lookup array to perform a binary search
/// on an offset within the text section on this array.
/// * Finally there is another array, with the same count as before, also of
/// 32-bit little-endian integers. These integers map 1:1 with the previous
/// array of offsets, and correspond to what the original offset was in the
/// wasm file.
///
/// Decoding this section is intentionally simple, it only requires loading a
/// 32-bit little-endian integer plus some bounds checks. Reading this section
/// is done with the `lookup_file_pos` function below. Reading involves
/// performing a binary search on the first array using the index found for the
/// native code offset to index into the second array and find the wasm code
/// offset.
///
/// At this time this section has an alignment of 1, which means all reads of it
/// are unaligned. Additionally at this time the 32-bit encodings chosen here
/// mean that >=4gb text sections are not supported.
pub const ELF_WASMTIME_ADDRMAP: &str = ".wasmtime.addrmap";
/// A custom binary-encoded section of wasmtime compilation artifacts which
/// encodes the ability to map an offset in the text section to the trap code
/// that it corresponds to.
///
/// This section is used at runtime to determine what flavor of trap happened to
/// ensure that embedders and debuggers know the reason for the wasm trap. The
/// encoding of this section is custom to Wasmtime and managed with helpers in
/// the `object` crate:
///
/// * First the section has a 32-bit little endian integer indicating how many
/// trap entries are in the section.
/// * Next is an array, of the same length as read before, of 32-bit
/// little-endian integers. These integers are offsets into the text section
/// of the compilation image.
/// * Finally is the same count number of bytes. Each of these bytes corresponds
/// to a trap code.
///
/// This section is decoded by `lookup_trap_code` below which will read the
/// section count, slice some bytes to get the various arrays, and then perform
/// a binary search on the offsets array to find the index corresponding to
/// the pc being looked up. If found the same index in the trap array (the array
/// of bytes) is the trap code for that offset.
///
/// Note that at this time this section has an alignment of 1. Additionally due
/// to the 32-bit encodings for offsets this doesn't support images >=4gb.
pub const ELF_WASMTIME_TRAPS: &str = ".wasmtime.traps";
/// A custom section which consists of just 1 byte which is either 0 or 1 as to
/// whether BTI is enabled.
pub const ELF_WASM_BTI: &str = ".wasmtime.bti";
/// A bincode-encoded section containing engine-specific metadata used to
/// double-check that an artifact can be loaded into the current host.
pub const ELF_WASM_ENGINE: &str = ".wasmtime.engine";
/// This is the name of the section in the final ELF image which contains
/// concatenated data segments from the original wasm module.
///
/// This section is simply a list of bytes and ranges into this section are
/// stored within a `Module` for each data segment. Memory initialization and
/// passive segment management all index data directly located in this section.
///
/// Note that this implementation does not afford any method of leveraging the
/// `data.drop` instruction to actually release the data back to the OS. The
/// data section is simply always present in the ELF image. If we wanted to
/// release the data it's probably best to figure out what the best
/// implementation is for it at the time given a particular set of constraints.
pub const ELF_WASM_DATA: &'static str = ".rodata.wasm";
/// This is the name of the section in the final ELF image which contains a
/// `bincode`-encoded `CompiledModuleInfo`.
///
/// This section is optionally decoded in `CompiledModule::from_artifacts`
/// depending on whether or not a `CompiledModuleInfo` is already available. In
/// cases like `Module::new` where compilation directly leads into consumption,
/// it's available. In cases like `Module::deserialize` this section must be
/// decoded to get all the relevant information.
pub const ELF_WASMTIME_INFO: &'static str = ".wasmtime.info";
/// This is the name of the section in the final ELF image which contains a
/// concatenated list of all function names.
///
/// This section is optionally included in the final artifact depending on
/// whether the wasm module has any name data at all (or in the future if we add
/// an option to not preserve name data). This section is a concatenated list of
/// strings where `CompiledModuleInfo::func_names` stores offsets/lengths into
/// this section.
///
/// Note that the goal of this section is to avoid having to decode names at
/// module-load time if we can. Names are typically only used for debugging or
/// things like backtraces so there's no need to eagerly load all of them. By
/// storing the data in a separate section the hope is that the data, which is
/// sometimes quite large (3MB seen for spidermonkey-compiled-to-wasm), can be
/// paged in lazily from an mmap and is never paged in if we never reference it.
pub const ELF_NAME_DATA: &'static str = ".name.wasm";
/// This is the name of the section in the final ELF image that contains the
/// concatenation of all the native DWARF information found in the original wasm
/// files.
///
/// This concatenation is not intended to be read by external tools at this time
/// and is instead indexed directly by relative indices stored in compilation
/// metadata.
pub const ELF_WASMTIME_DWARF: &str = ".wasmtime.dwarf";
macro_rules! libcalls {
($($rust:ident = $sym:tt)*) => (
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, Ord, PartialOrd)]
#[allow(missing_docs)]
pub enum LibCall {
$($rust,)*
}
impl LibCall {
/// Returns the libcall corresponding to the provided symbol name,
/// if one matches.
pub fn from_str(s: &str) -> Option<LibCall> {
match s {
$($sym => Some(LibCall::$rust),)*
_ => None,
}
}
/// Returns the symbol name in object files associated with this
/// libcall.
pub fn symbol(&self) -> &'static str {
match self {
$(LibCall::$rust => $sym,)*
}
}
}
)
}
libcalls! {
FloorF32 = "libcall_floor32"
FloorF64 = "libcall_floor64"
NearestF32 = "libcall_nearestf32"
NearestF64 = "libcall_nearestf64"
CeilF32 = "libcall_ceilf32"
CeilF64 = "libcall_ceilf64"
TruncF32 = "libcall_truncf32"
TruncF64 = "libcall_truncf64"
FmaF32 = "libcall_fmaf32"
FmaF64 = "libcall_fmaf64"
X86Pshufb = "libcall_x86_pshufb"
}