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>
54 lines
1.6 KiB
LLVM
54 lines
1.6 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
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; RUN: opt --bpf-check-and-opt-ir -S -mtriple=bpf-pc-linux < %s | FileCheck %s
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; Generated from the following C code:
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;
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; #define __uptr __attribute__((address_space(1)))
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;
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; extern int __uptr *magic1();
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; extern int __uptr *magic2();
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;
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; void test(long i) {
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; int __uptr *a;
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;
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; if (i > 42)
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; a = magic1();
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; else
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; a = magic2();
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; a[5] = 7;
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; }
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;
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; Using the following command:
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;
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; clang --target=bpf -O2 -S -emit-llvm -o t.ll t.c
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define void @test(i64 noundef %i) {
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; CHECK: if.end:
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; CHECK-NEXT: [[A_0:%.*]] = phi ptr addrspace(1)
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; CHECK-NEXT: [[A_01:%.*]] = addrspacecast ptr addrspace(1) [[A_0]] to ptr
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; CHECK-NEXT: [[ARRAYIDX2:%.*]] = getelementptr inbounds i32, ptr [[A_01]], i64 5
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; CHECK-NEXT: store i32 7, ptr [[ARRAYIDX2]], align 4
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; CHECK-NEXT: ret void
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;
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entry:
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%cmp = icmp sgt i64 %i, 42
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br i1 %cmp, label %if.then, label %if.else
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if.then: ; preds = %entry
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%call = tail call ptr addrspace(1) @magic1()
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br label %if.end
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if.else: ; preds = %entry
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%call1 = tail call ptr addrspace(1) @magic2()
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br label %if.end
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if.end: ; preds = %if.else, %if.then
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%a.0 = phi ptr addrspace(1) [ %call, %if.then ], [ %call1, %if.else ]
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%arrayidx = getelementptr inbounds i32, ptr addrspace(1) %a.0, i64 5
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store i32 7, ptr addrspace(1) %arrayidx, align 4
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ret void
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}
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declare ptr addrspace(1) @magic1(...)
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declare ptr addrspace(1) @magic2(...)
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