> On Wed, Nov 22, 2023 at 10:08 AM Yonghong Song <yonghong.song@xxxxxxxxx> wrote:
>>
>> > +SEC("?tc")
>> > +__log_level(2)
>> > +int test_verifier_range(void)
>> > +{
>> > + asm volatile (
>> > + "r5 = 100; \
>> > + r5 /= 3; \
>> > + w5 >>= 7; \
>> > + r5 &= -386969681; \
>> > + r5 -= -884670597; \
>> > + w0 = w5; \
>> > + if w0 & 0x894b6a55 goto +2; \
>>
>> So actually it is 'if w0 & 0x894b6a55 goto +2' failed
>> the compilation.
>>
>> Indeed, the above operation is not supported in llvm.
>> See
>> https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/BPF/BPFInstrFormats.td#L62-L74
>> the missing BPFJumpOp<0x4> which corresponds to JSET.
>>
>> The following llvm patch (on top of llvm-project main branch):
>>
>> diff --git a/llvm/lib/Target/BPF/BPFInstrFormats.td b/llvm/lib/Target/BPF/BPFInstrFormats.td
>> index 841d97efc01c..6ed83d877ac0 100644
>> --- a/llvm/lib/Target/BPF/BPFInstrFormats.td
>> +++ b/llvm/lib/Target/BPF/BPFInstrFormats.td
>> @@ -63,6 +63,7 @@ def BPF_JA : BPFJumpOp<0x0>;
>> def BPF_JEQ : BPFJumpOp<0x1>;
>> def BPF_JGT : BPFJumpOp<0x2>;
>> def BPF_JGE : BPFJumpOp<0x3>;
>> +def BPF_JSET : BPFJumpOp<0x4>;
>> def BPF_JNE : BPFJumpOp<0x5>;
>> def BPF_JSGT : BPFJumpOp<0x6>;
>> def BPF_JSGE : BPFJumpOp<0x7>;
>> diff --git a/llvm/lib/Target/BPF/BPFInstrInfo.td b/llvm/lib/Target/BPF/BPFInstrInfo.td
>> index 305cbbd34d27..9e75f35efe70 100644
>> --- a/llvm/lib/Target/BPF/BPFInstrInfo.td
>> +++ b/llvm/lib/Target/BPF/BPFInstrInfo.td
>> @@ -246,6 +246,70 @@ class JMP_RI_32<BPFJumpOp Opc, string OpcodeStr, PatLeaf Cond>
>> let BPFClass = BPF_JMP32;
>> }
>>
>> +class JSET_RR<string OpcodeStr>
>> + : TYPE_ALU_JMP<BPF_JSET.Value, BPF_X.Value,
>> + (outs),
>> + (ins GPR:$dst, GPR:$src, brtarget:$BrDst),
>> + "if $dst "#OpcodeStr#" $src goto $BrDst",
>> + []> {
>> + bits<4> dst;
>> + bits<4> src;
>> + bits<16> BrDst;
>> +
>> + let Inst{55-52} = src;
>> + let Inst{51-48} = dst;
>> + let Inst{47-32} = BrDst;
>> + let BPFClass = BPF_JMP;
>> +}
>> +
>> +class JSET_RI<string OpcodeStr>
>> + : TYPE_ALU_JMP<BPF_JSET.Value, BPF_K.Value,
>> + (outs),
>> + (ins GPR:$dst, i64imm:$imm, brtarget:$BrDst),
>> + "if $dst "#OpcodeStr#" $imm goto $BrDst",
>> + []> {
>> + bits<4> dst;
>> + bits<16> BrDst;
>> + bits<32> imm;
>> +
>> + let Inst{51-48} = dst;
>> + let Inst{47-32} = BrDst;
>> + let Inst{31-0} = imm;
>> + let BPFClass = BPF_JMP;
>> +}
>> +
>> +class JSET_RR_32<string OpcodeStr>
>> + : TYPE_ALU_JMP<BPF_JSET.Value, BPF_X.Value,
>> + (outs),
>> + (ins GPR32:$dst, GPR32:$src, brtarget:$BrDst),
>> + "if $dst "#OpcodeStr#" $src goto $BrDst",
>> + []> {
>> + bits<4> dst;
>> + bits<4> src;
>> + bits<16> BrDst;
>> +
>> + let Inst{55-52} = src;
>> + let Inst{51-48} = dst;
>> + let Inst{47-32} = BrDst;
>> + let BPFClass = BPF_JMP32;
>> +}
>> +
>> +class JSET_RI_32<string OpcodeStr>
>> + : TYPE_ALU_JMP<BPF_JSET.Value, BPF_K.Value,
>> + (outs),
>> + (ins GPR32:$dst, i32imm:$imm, brtarget:$BrDst),
>> + "if $dst "#OpcodeStr#" $imm goto $BrDst",
>> + []> {
>> + bits<4> dst;
>> + bits<16> BrDst;
>> + bits<32> imm;
>> +
>> + let Inst{51-48} = dst;
>> + let Inst{47-32} = BrDst;
>> + let Inst{31-0} = imm;
>> + let BPFClass = BPF_JMP32;
>> +}
>> +
>> multiclass J<BPFJumpOp Opc, string OpcodeStr, PatLeaf Cond, PatLeaf Cond32> {
>> def _rr : JMP_RR<Opc, OpcodeStr, Cond>;
>> def _ri : JMP_RI<Opc, OpcodeStr, Cond>;
>> @@ -265,6 +329,10 @@ defm JULT : J<BPF_JLT, "<", BPF_CC_LTU, BPF_CC_LTU_32>;
>> defm JULE : J<BPF_JLE, "<=", BPF_CC_LEU, BPF_CC_LEU_32>;
>> defm JSLT : J<BPF_JSLT, "s<", BPF_CC_LT, BPF_CC_LT_32>;
>> defm JSLE : J<BPF_JSLE, "s<=", BPF_CC_LE, BPF_CC_LE_32>;
>> +def JSET_RR : JSET_RR<"&">;
>> +def JSET_RI : JSET_RI<"&">;
>> +def JSET_RR_32 : JSET_RR_32<"&">;
>> +def JSET_RI_32 : JSET_RI_32<"&">;
>> }
>>
>> // ALU instructions
>>
>> can solve your inline asm issue. We will discuss whether llvm compiler
>> should be implementing this instruction from source or not.
>
> I'd say 'yes'. clang/llvm should support such asm syntax.
>
> Jose, Eduard,
> Thoughts?
We already support it in GAS:
$ echo 'if w0 & 0x894b6a55 goto +2' | bpf-unknown-none-as -mdialect=pseudoc -
$ bpf-unknown-none-objdump -M hex,pseudoc -d a.out
a.out: file format elf64-bpfle
Disassembly of section .text:
0000000000000000 <.text>:
0: 46 00 02 00 55 6a 4b 89 if w0&0x894b6a55 goto 0x2
We weren't aware we were diverging with llvm by doing so. We support
syntax for all the conditional jump instructions using the following
operators:
BPF_JEQ ==
BPF_JGT >
BPF_JSGT s>
BPF_JGE >=
BPF_JSGE s>=
BPF_JLT <
BPF_JLST s<
BPF_JLE <=
BPF_JSLE s<=
BPF_JSET &
BPF_JNE !=
