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src: Use llvm.readsteadycounter on Linux RISC-V

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Why `rdcycle` is kernel only while `rdtime` is not is a mystery to me.
This commit is contained in:
Yawning Angel
2026-08-02 21:03:11 +09:00
parent 280f02f4ef
commit cd08f535c8
1 changed files with 12 additions and 0 deletions
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12
src/llvm_backend_proc.cpp
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@@ -3418,6 +3418,18 @@ gb_internal lbValue lb_build_builtin_proc(lbProcedure *p, Ast *expr, TypeAndValu
LLVMValueRef the_asm = llvm_get_inline_asm(func_type, str_lit("mrs $0, cntvct_el0"), str_lit("=r"), has_side_effects);
GB_ASSERT(the_asm != nullptr);
res.value = LLVMBuildCall2(p->builder, func_type, the_asm, nullptr, 0, "");
#if LLVM_VERSION_MAJOR > 19 || (LLVM_VERSION_MAJOR == 19 && LLVM_VERSION_MINOR >= 1)
} else if (build_context.metrics.arch == TargetArch_riscv64 && build_context.metrics.os == TargetOs_linux) {
// Linux in it's infinite wisdom decided that `rdcycle` should not be
// available to userland past Linux 6.6. Some inline assembly with
// `rdtime` would also work, but LLVM issue #117701 suggests just
// using this intrinsic.
//
// Support for this was introduced in commit `b8ed69e`, and is present
// in LLVM tags 19.1.0-rc1.
char const *name = "llvm.readsteadycounter";
res.value = lb_call_intrinsic(p, name, nullptr, 0, nullptr, 0);
#endif
} else {
char const *name = "llvm.readcyclecounter";
res.value = lb_call_intrinsic(p, name, nullptr, 0, nullptr, 0);