[llvm-bugs] [Bug 33369] New: BPF target: code generation with shifts around ptr types

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=33369

            Bug ID: 33369
           Summary: BPF target: code generation with shifts around ptr
                    types
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: daniel at iogearbox.net
                CC: llvm-bugs at lists.llvm.org

We've seen code generated for the BPF ctx (XDP in this case) that looks as
follows:

[...]
; new_dst.p4 |= svc->rev_nat_index;
     704:       r3 <<= 8
     705:       r3 |= r4
; if (svc->rev_nat_index)
     706:       r2 |= r3
; memcpy(ptr, from, len);
     707:       *(u8 *)(r1 + 50) = r2
     708:       r2 >>= 8
     709:       *(u8 *)(r1 + 51) = r2
     710:       r2 = *(u32 *)(r6 + 4)   ; XDP data_end (rewrite to ptr load)
     711:       r1 = *(u32 *)(r6 + 0)   ; XDP data (rewrite to ptr load)

LBB0_107:
     712:       r3 = 4294967142ll
; void *end = (void *)(long) xdp->data_end;
     714:       r2 <<= 32               ; buggy (destroys ptr)
     715:       r2 >>= 32               ; buggy
; void *data = (void *)(long) xdp->data;
     716:       r1 <<= 32               ; buggy (destroys ptr)
     717:       r1 >>= 32               ; buggy
; if (data + sizeof(*ptr) > end)
     718:       r4 = r1
     719:       r4 += 2
     720:       if r4 > r2 goto 3
; *(__u16 *) data = 1;//csum;
     721:       r2 = 1
     722:       *(u16 *)(r1 + 0) = r2
     723:       r3 = 0
[...]

$ clang --version
clang version 5.0.0 (https://github.com/llvm-mirror/clang.git
91d84ed65dd3629b4536cf393850ecfdfd3f1be5)
(https://github.com/llvm-mirror/llvm.git
2385754c5e1ce0689b4295a3e13e1a47215b850d)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin

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