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

2 files changed, 44 insertions, 0 deletions

diff --git a/compiler/rustc_target/src/asm/mod.rs b/compiler/rustc_target/src/asm/mod.rs
index 1292f46f0c9..f17452b3ba0 100644
--- a/compiler/rustc_target/src/asm/mod.rs
+++ b/compiler/rustc_target/src/asm/mod.rs
@@ -934,6 +934,7 @@ pub enum InlineAsmClobberAbi {
     LoongArch,
     PowerPC,
     S390x,
+    Bpf,
     Msp430,
 }
 
@@ -1003,6 +1004,10 @@ impl InlineAsmClobberAbi {
                 "C" | "system" => Ok(InlineAsmClobberAbi::S390x),
                 _ => Err(&["C", "system"]),
             },
+            InlineAsmArch::Bpf => match name {
+                "C" | "system" => Ok(InlineAsmClobberAbi::Bpf),
+                _ => Err(&["C", "system"]),
+            },
             InlineAsmArch::Msp430 => match name {
                 "C" | "system" => Ok(InlineAsmClobberAbi::Msp430),
                 _ => Err(&["C", "system"]),
@@ -1278,6 +1283,14 @@ impl InlineAsmClobberAbi {
                     a8, a9, a10, a11, a12, a13, a14, a15,
                 }
             },
+            InlineAsmClobberAbi::Bpf => clobbered_regs! {
+                Bpf BpfInlineAsmReg {
+                    // Refs: Section 1.1 "Registers and calling convention" in BPF ABI Recommended Conventions and Guidelines v1.0
+                    // https://www.kernel.org/doc/html/latest/bpf/standardization/abi.html#registers-and-calling-convention
+
+                    r0, r1, r2, r3, r4, r5,
+                }
+            },
             InlineAsmClobberAbi::Msp430 => clobbered_regs! {
                 Msp430 Msp430InlineAsmReg {
                     r11, r12, r13, r14, r15,
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));
+}