Rollup merge of #136194 - taiki-e:bpf-clobber-abi, r=amanieu

Support clobber_abi in BPF inline assembly

This supports [`clobber_abi`](https://doc.rust-lang.org/nightly/reference/inline-assembly.html#abi-clobbers) which is one of the requirements of stabilization mentioned in the tracking Issue for `asm_experimental_arch` (#93335).

Refs: [Section 1.1 "Registers and calling convention" in BPF ABI Recommended Conventions and Guidelines v1.0](https://github.com/torvalds/linux/blob/v6.13/Documentation/bpf/standardization/abi.rst#11registers-and-calling-convention)
> R0 - R5 are scratch registers and BPF programs needs to spill/fill them if necessary across calls.

cc `@alessandrod` `@dave-tucker` `@tamird` `@vadorovsky` (target maintainers mentioned in platform support document which will be added by https://github.com/rust-lang/rust/pull/135107)

r? `@Amanieu`

`@rustbot` label +O-eBPF +A-inline-assembly

1 files changed, 31 insertions, 0 deletions

diff --git a/tests/codegen/asm/bpf-clobbers.rs b/tests/codegen/asm/bpf-clobbers.rs
new file mode 100644
index 00000000000..1117549b1ec
--- /dev/null
+++ b/tests/codegen/asm/bpf-clobbers.rs
@@ -0,0 +1,31 @@
+//@ add-core-stubs
+//@ compile-flags: --target bpfel-unknown-none
+//@ needs-llvm-components: bpf
+
+#![crate_type = "rlib"]
+#![feature(no_core, asm_experimental_arch)]
+#![no_core]
+
+extern crate minicore;
+use minicore::*;
+
+// CHECK-LABEL: @flags_clobber
+// CHECK: call void asm sideeffect "", ""()
+#[no_mangle]
+pub unsafe fn flags_clobber() {
+    asm!("", options(nostack, nomem));
+}
+
+// CHECK-LABEL: @no_clobber
+// CHECK: call void asm sideeffect "", ""()
+#[no_mangle]
+pub unsafe fn no_clobber() {
+    asm!("", options(nostack, nomem, preserves_flags));
+}
+
+// CHECK-LABEL: @clobber_abi
+// CHECK: asm sideeffect "", "={r0},={r1},={r2},={r3},={r4},={r5}"()
+#[no_mangle]
+pub unsafe fn clobber_abi() {
+    asm!("", clobber_abi("C"), options(nostack, nomem, preserves_flags));
+}