2aacb56e83
This commit aims to support BPF arena kernel side [feature](https://lore.kernel.org/bpf/20240209040608.98927-1-alexei.starovoitov@gmail.com/): - arena is a memory region accessible from both BPF program and userspace; - base pointers for this memory region differ between kernel and user spaces; - `dst_reg = addr_space_cast(src_reg, dst_addr_space, src_addr_space)` translates src_reg, a pointer in src_addr_space to dst_reg, equivalent pointer in dst_addr_space, {src,dst}_addr_space are immediate constants; - number 0 is assigned to kernel address space; - number 1 is assigned to user address space. On the LLVM side, the goal is to make load and store operations on arena pointers "transparent" for BPF programs: - assume that pointers with non-zero address space are pointers to arena memory; - assume that arena is identified by address space number; - assume that address space zero corresponds to kernel address space; - assume that every BPF-side load or store from arena is done via pointer in user address space, thus convert base pointers using `addr_space_cast(src_reg, 0, 1)`; Only load, store, cmpxchg and atomicrmw IR instructions are handled by this transformation. For example, the following C code: ```c #define __as __attribute__((address_space(1))) void copy(int __as *from, int __as *to) { *to = *from; } ``` Compiled to the following IR: ```llvm define void @copy(ptr addrspace(1) %from, ptr addrspace(1) %to) { entry: %0 = load i32, ptr addrspace(1) %from, align 4 store i32 %0, ptr addrspace(1) %to, align 4 ret void } ``` Is transformed to: ```llvm %to2 = addrspacecast ptr addrspace(1) %to to ptr ;; ! %from1 = addrspacecast ptr addrspace(1) %from to ptr ;; ! %0 = load i32, ptr %from1, align 4, !tbaa !3 store i32 %0, ptr %to2, align 4, !tbaa !3 ret void ``` And compiled as: ```asm r2 = addr_space_cast(r2, 0, 1) r1 = addr_space_cast(r1, 0, 1) r1 = *(u32 *)(r1 + 0) *(u32 *)(r2 + 0) = r1 exit ``` Co-authored-by: Eduard Zingerman <eddyz87@gmail.com>
23 lines
932 B
LLVM
23 lines
932 B
LLVM
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
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; RUN: llc -march=bpfel -mcpu=v4 -filetype=asm -show-mc-encoding < %s | FileCheck %s
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define ptr addrspace(1) @foo(ptr %p) {
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; CHECK-LABEL: foo:
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; CHECK: # %bb.0: # %entry
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; CHECK-NEXT: r0 = addr_space_cast(r1, 1, 0) # encoding: [0xbf,0x10,0x01,0x00,0x00,0x00,0x01,0x00]
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; CHECK-NEXT: exit # encoding: [0x95,0x00,0x00,0x00,0x00,0x00,0x00,0x00]
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entry:
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%0 = addrspacecast ptr %p to ptr addrspace(1)
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ret ptr addrspace(1) %0
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}
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define ptr @bar(ptr addrspace(1) %p) {
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; CHECK-LABEL: bar:
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; CHECK: # %bb.0: # %entry
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; CHECK-NEXT: r0 = addr_space_cast(r1, 0, 1) # encoding: [0xbf,0x10,0x01,0x00,0x01,0x00,0x00,0x00]
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; CHECK-NEXT: exit # encoding: [0x95,0x00,0x00,0x00,0x00,0x00,0x00,0x00]
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entry:
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%0 = addrspacecast ptr addrspace(1) %p to ptr
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ret ptr %0
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}
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