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[bpf] Fix memory offset check for loads and stores

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If the offset cannot fit into the instruction, an addition to the
pointer is emitted before the actual access. However, BPF offsets are
16-bit but LLVM considers them to be, for the matter of this check,
to be 32-bit long.

This causes the following program:

int bpf_prog1(void *ign)
{

volatile unsigned long t = 0x8983984739ull;
return *(unsigned long *)((0xffffffff8fff0002ull) + t);

}

To generate the following (wrong) code:

0: 18 01 00 00 39 47 98 83 00 00 00 00 89 00 00 00

r1 = 590618314553ll

2: 7b 1a f8 ff 00 00 00 00 *(u64 *)(r10 - 8) = r1
3: 79 a1 f8 ff 00 00 00 00 r1 = *(u64 *)(r10 - 8)
4: 79 10 02 00 00 00 00 00 r0 = *(u64 *)(r1 + 2)
5: 95 00 00 00 00 00 00 00 exit

Fix it by changing the offset check to 16-bit.

Patch by Nadav Amit <nadav.amit@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Differential Revision: https://reviews.llvm.org/D32055

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300269 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Alexei Starovoitov 2017-04-13 22:24:13 +00:00
parent 1130138bb1
commit c67ef6aaf7
2 changed files with 19 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
lib/Target/BPF/BPFISelDAGToDAG.cpp
View File

@ -71,7 +71,7 @@ bool BPFDAGToDAGISel::SelectAddr(SDValue Addr, SDValue &Base, SDValue &Offset) {
// Addresses of the form Addr+const or Addr|const
if (CurDAG->isBaseWithConstantOffset(Addr)) {
ConstantSDNode *CN = dyn_cast<ConstantSDNode>(Addr.getOperand(1));
if (isInt<32>(CN->getSExtValue())) {
if (isInt<16>(CN->getSExtValue())) {
// If the first operand is a FI, get the TargetFI Node
if (FrameIndexSDNode *FIN =
@ -99,7 +99,7 @@ bool BPFDAGToDAGISel::SelectFIAddr(SDValue Addr, SDValue &Base, SDValue &Offset)
// Addresses of the form Addr+const or Addr|const
ConstantSDNode *CN = dyn_cast<ConstantSDNode>(Addr.getOperand(1));
if (isInt<32>(CN->getSExtValue())) {
if (isInt<16>(CN->getSExtValue())) {
// If the first operand is a FI, get the TargetFI Node
if (FrameIndexSDNode *FIN =

17
test/CodeGen/BPF/mem_offset.ll Normal file
View File

@ -0,0 +1,17 @@
; RUN: llc -march=bpfel -show-mc-encoding < %s | FileCheck %s
; Function Attrs: nounwind
define i32 @bpf_prog1(i8* nocapture readnone) local_unnamed_addr #0 {
; CHECK: r1 += -1879113726 # encoding: [0x07,0x01,0x00,0x00,0x02,0x00,0xff,0x8f]
; CHECK: r0 = *(u64 *)(r1 + 0) # encoding: [0x79,0x10,0x00,0x00,0x00,0x00,0x00,0x00]
%2 = alloca i64, align 8
%3 = bitcast i64* %2 to i8*
store volatile i64 590618314553, i64* %2, align 8
%4 = load volatile i64, i64* %2, align 8
%5 = add i64 %4, -1879113726
%6 = inttoptr i64 %5 to i64*
%7 = load i64, i64* %6, align 8
%8 = trunc i64 %7 to i32
ret i32 %8
}