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51781c98c2
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
llvm-svn: 300269
18 lines
617 B
LLVM
18 lines
617 B
LLVM
; RUN: llc -march=bpfel -show-mc-encoding < %s | FileCheck %s
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; Function Attrs: nounwind
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define i32 @bpf_prog1(i8* nocapture readnone) local_unnamed_addr #0 {
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; CHECK: r1 += -1879113726 # encoding: [0x07,0x01,0x00,0x00,0x02,0x00,0xff,0x8f]
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; CHECK: r0 = *(u64 *)(r1 + 0) # encoding: [0x79,0x10,0x00,0x00,0x00,0x00,0x00,0x00]
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%2 = alloca i64, align 8
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%3 = bitcast i64* %2 to i8*
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store volatile i64 590618314553, i64* %2, align 8
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%4 = load volatile i64, i64* %2, align 8
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%5 = add i64 %4, -1879113726
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%6 = inttoptr i64 %5 to i64*
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%7 = load i64, i64* %6, align 8
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%8 = trunc i64 %7 to i32
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ret i32 %8
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}
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