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>
27 lines
1.1 KiB
LLVM
27 lines
1.1 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
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; RUN: opt -passes=bpf-aspace-simplify -mtriple=bpf-pc-linux -S < %s | FileCheck %s
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; Check that when bpf-aspace-simplify pass modifies chain
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; 'cast M->N -> GEP -> cast N->M' it does not remove GEP,
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; when that GEP is used by some other instruction.
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define dso_local ptr addrspace(1) @test (ptr addrspace(1) %p) {
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; CHECK-LABEL: define dso_local ptr addrspace(1) @test(
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; CHECK-SAME: ptr addrspace(1) [[P:%.*]]) {
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[A:%.*]] = addrspacecast ptr addrspace(1) [[P]] to ptr
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; CHECK-NEXT: [[B:%.*]] = getelementptr inbounds i8, ptr [[A]], i64 8
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; CHECK-NEXT: [[B1:%.*]] = getelementptr inbounds i8, ptr addrspace(1) [[P]], i64 8
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; CHECK-NEXT: call void @sink(ptr [[B]])
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; CHECK-NEXT: ret ptr addrspace(1) [[B1]]
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;
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entry:
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%a = addrspacecast ptr addrspace(1) %p to ptr
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%b = getelementptr inbounds i8, ptr %a, i64 8
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%c = addrspacecast ptr %b to ptr addrspace(1)
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call void @sink(ptr %b)
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ret ptr addrspace(1) %c
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}
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declare dso_local void @sink(ptr)
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