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stage2 macho: first, rough draft at trampolining

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Jakub Konka
2020-11-24 18:46:43 +01:00
parent 80b1041c21
commit ef5132c508
3 changed files with 88 additions and 86 deletions
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63
src/codegen.zig
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@@ -2767,24 +2767,51 @@ fn Function(comptime arch: std.Target.Cpu.Arch) type {
// For MachO, the binary, with the exception of object files, has to be a PIE.
// Therefore, we cannot load an absolute address.
assert(x > math.maxInt(u32)); // 32bit direct addressing is not supported by MachO.
// The plan here is to use RIP-relative addressing, but leaving the actual displacement
// information empty (0-padded) and fixing it up later in the linker.
try self.mod_fn.owner_decl.link.macho.addRipPosition(self.bin_file.allocator, .{
.address = x,
.start = self.code.items.len,
.len = 7,
});
try self.code.ensureCapacity(self.code.items.len + 9);
// leaq %r, [rip + disp]
self.code.appendSliceAssumeCapacity(&[_]u8{
0x48,
0x8d,
0x05 | (@as(u8, reg.id() & 0b111) << 3), // R
0x0,
0x0,
0x0,
0x0,
});
// The plan here is to use unconditional relative jump to GOT entry, where we store
// pre-calculated and stored effective address to load into the target register.
// We leave the actual displacement information empty (0-padded) and fixing it up
// later in the linker.
if (reg.id() == 0) { // %rax is special-cased
try self.code.ensureCapacity(self.code.items.len + 5);
try self.mod_fn.owner_decl.link.macho.addRipPosition(self.bin_file.allocator, .{
.address = x,
.start = self.code.items.len,
.len = 5,
});
// call [label]
self.code.appendSliceAssumeCapacity(&[_]u8{
0xE8,
0x0,
0x0,
0x0,
0x0,
});
} else {
try self.code.ensureCapacity(self.code.items.len + 10);
// push %rax
self.code.appendSliceAssumeCapacity(&[_]u8{0x50});
try self.mod_fn.owner_decl.link.macho.addRipPosition(self.bin_file.allocator, .{
.address = x,
.start = self.code.items.len,
.len = 5,
});
// call [label]
self.code.appendSliceAssumeCapacity(&[_]u8{
0xE8,
0x0,
0x0,
0x0,
0x0,
});
// mov %r, %rax
self.code.appendSliceAssumeCapacity(&[_]u8{
0x48,
0x89,
0xC0 | @as(u8, reg.id()),
});
// pop %rax
self.code.appendSliceAssumeCapacity(&[_]u8{0x58});
}
} else if (x <= math.maxInt(u32)) {
// Moving from memory to a register is a variant of `8B /r`.
// Since we're using 64-bit moves, we require a REX.