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Prevent register clobbering on x86_64 threadlocal access

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On the x86_64 self hosted backend, thread locals are accessed through
__tls_get_addr on PIC. Usually this goes through a fast path which does
not lose any registers, however in some cases (notably any dlopened
library on my machine) this can take a slow path which calls out to C
ABI functions

Catch this case and backup registers as necessary

Fix a few other ones while we're here. Credit to mlugg

Fixes #30183
This commit is contained in:
Mick Sayson 2025-12-15 17:07:34 -08:00 • committed by mlugg
parent b9eefe17af
commit fc78a61c4c
1 changed files with 32 additions and 4 deletions
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36
src/codegen/x86_64/CodeGen.zig
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@ -173048,11 +173048,39 @@ fn genBody(cg: *CodeGen, body: []const Air.Inst.Index) InnerError!void {
const ty_nav = air_datas[@intFromEnum(inst)].ty_nav;
const nav = ip.getNav(ty_nav.nav);
const is_threadlocal = zcu.comp.config.any_non_single_threaded and nav.isThreadlocal(ip);
if (is_threadlocal) if (cg.target.ofmt == .coff or cg.mod.pic) {
try cg.spillRegisters(&.{ .rdi, .rax });
} else {
try cg.spillRegisters(&.{.rax});
if (is_threadlocal) switch (cg.target.ofmt) {
.elf => if (cg.mod.pic) {
// LD model: `__tls_get_addr` uses the standard ABI
try cg.spillEflagsIfOccupied();
try cg.spillRegisters(abi.getCallerPreservedRegs(.x86_64_sysv));
} else {
// LE model: manual lowering uses these two registers
try cg.spillRegisters(&.{ .rdi, .rax });
},
.coff => {
// manual lowering uses these registers
try cg.spillRegisters(&.{ .rdi, .rax });
},
.macho => switch (cg.target.cpu.arch) {
.x86 => {
// `tlv_get_addr` returns in eax, clobbers ecx, preserves other GPRs
try cg.spillEflagsIfOccupied();
try cg.spillRegisters(&.{ .rax, .rcx });
},
.x86_64 => {
// `tlv_get_addr` returns in rax, preserves other GPRs
try cg.spillEflagsIfOccupied();
try cg.spillRegisters(&.{.rax});
},
else => unreachable,
},
else => unreachable,
};
var res = try cg.tempInit(.fromInterned(ty_nav.ty), .{ .lea_nav = ty_nav.nav });
if (is_threadlocal) while (try res.toRegClass(true, .general_purpose, cg)) {};
try res.finish(inst, &.{}, &.{}, cg);