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SN6PR1501MB2064.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Jul 2021 22:54:31.5501 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: b8qIpf1+pmThxtRKBBheu+CLWis57CobHCOEu8Se/ktvCn25uEa2TRIJN8fHfN+b X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR15MB4839 X-OriginatorOrg: fb.com X-Proofpoint-ORIG-GUID: HDzTgD_RHEw9b9sX9za1tLA-F4mUyzWK X-Proofpoint-GUID: HDzTgD_RHEw9b9sX9za1tLA-F4mUyzWK X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-07-29_17:2021-07-29,2021-07-29 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 suspectscore=0 adultscore=0 priorityscore=1501 mlxlogscore=999 impostorscore=0 clxscore=1015 lowpriorityscore=0 spamscore=0 mlxscore=0 phishscore=0 malwarescore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2107290138 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 7/29/21 2:17 PM, Johan Almbladh wrote: > On Thu, Jul 29, 2021 at 1:52 AM Yonghong Song wrote: >>> + /* >>> + * Register (non-)clobbering test, in the case where a 32-bit >>> + * JIT implements complex ALU64 operations via function calls. >>> + */ >>> + "INT: Register clobbering, R1 updated", >>> + .u.insns_int = { >>> + BPF_ALU32_IMM(BPF_MOV, R0, 0), >>> + BPF_ALU32_IMM(BPF_MOV, R1, 123456789), >>> + BPF_ALU32_IMM(BPF_MOV, R2, 2), >>> + BPF_ALU32_IMM(BPF_MOV, R3, 3), >>> + BPF_ALU32_IMM(BPF_MOV, R4, 4), >>> + BPF_ALU32_IMM(BPF_MOV, R5, 5), >>> + BPF_ALU32_IMM(BPF_MOV, R6, 6), >>> + BPF_ALU32_IMM(BPF_MOV, R7, 7), >>> + BPF_ALU32_IMM(BPF_MOV, R8, 8), >>> + BPF_ALU32_IMM(BPF_MOV, R9, 9), >>> + BPF_ALU64_IMM(BPF_DIV, R1, 123456789), >>> + BPF_JMP_IMM(BPF_JNE, R0, 0, 10), >>> + BPF_JMP_IMM(BPF_JNE, R1, 1, 9), >>> + BPF_JMP_IMM(BPF_JNE, R2, 2, 8), >>> + BPF_JMP_IMM(BPF_JNE, R3, 3, 7), >>> + BPF_JMP_IMM(BPF_JNE, R4, 4, 6), >>> + BPF_JMP_IMM(BPF_JNE, R5, 5, 5), >>> + BPF_JMP_IMM(BPF_JNE, R6, 6, 4), >>> + BPF_JMP_IMM(BPF_JNE, R7, 7, 3), >>> + BPF_JMP_IMM(BPF_JNE, R8, 8, 2), >>> + BPF_JMP_IMM(BPF_JNE, R9, 9, 1), >>> + BPF_ALU32_IMM(BPF_MOV, R0, 1), >>> + BPF_EXIT_INSN(), >>> + }, >>> + INTERNAL, >>> + { }, >>> + { { 0, 1 } } >>> + }, >>> + { >>> + "INT: Register clobbering, R2 updated", >>> + .u.insns_int = { >>> + BPF_ALU32_IMM(BPF_MOV, R0, 0), >>> + BPF_ALU32_IMM(BPF_MOV, R1, 1), >>> + BPF_ALU32_IMM(BPF_MOV, R2, 2 * 123456789), >>> + BPF_ALU32_IMM(BPF_MOV, R3, 3), >>> + BPF_ALU32_IMM(BPF_MOV, R4, 4), >>> + BPF_ALU32_IMM(BPF_MOV, R5, 5), >>> + BPF_ALU32_IMM(BPF_MOV, R6, 6), >>> + BPF_ALU32_IMM(BPF_MOV, R7, 7), >>> + BPF_ALU32_IMM(BPF_MOV, R8, 8), >>> + BPF_ALU32_IMM(BPF_MOV, R9, 9), >>> + BPF_ALU64_IMM(BPF_DIV, R2, 123456789), >>> + BPF_JMP_IMM(BPF_JNE, R0, 0, 10), >>> + BPF_JMP_IMM(BPF_JNE, R1, 1, 9), >>> + BPF_JMP_IMM(BPF_JNE, R2, 2, 8), >>> + BPF_JMP_IMM(BPF_JNE, R3, 3, 7), >>> + BPF_JMP_IMM(BPF_JNE, R4, 4, 6), >>> + BPF_JMP_IMM(BPF_JNE, R5, 5, 5), >>> + BPF_JMP_IMM(BPF_JNE, R6, 6, 4), >>> + BPF_JMP_IMM(BPF_JNE, R7, 7, 3), >>> + BPF_JMP_IMM(BPF_JNE, R8, 8, 2), >>> + BPF_JMP_IMM(BPF_JNE, R9, 9, 1), >>> + BPF_ALU32_IMM(BPF_MOV, R0, 1), >>> + BPF_EXIT_INSN(), >>> + }, >>> + INTERNAL, >>> + { }, >>> + { { 0, 1 } } >>> + }, >> >> It looks like the above two tests, "R1 updated" and "R2 updated" should >> be very similar and the only difference is one immediate is 123456789 >> and another is 2 * 123456789. But for generated code, they all just have >> the final immediate. Could you explain what the difference in terms of >> jit for the above two tests? > > When a BPF_CALL instruction is executed, the eBPF assembler have > already saved any caller-saved registers that must be preserved, put > the arguments in R1-R5, and expects a return value in R0. It is just > for the JIT to emit the call. > > Not so when an eBPF instruction is implemented by a function call, > like ALU64 DIV in a 32-bit JIT. In this case, the function call is > unexpected by the eBPF assembler, and must be invisible to it. Now the > JIT must take care of saving all caller-saved registers on stack, put > the operands in the right argument registers, put the return value in > the destination register, and finally restore all caller-saved > registers without overwriting the computed result. > > The test checks that all other registers retain their value after such > a hidden function call. However, one register will contain the result. > In order to verify that all registers are saved and restored properly, > we must vary the destination and run it two times. It is not the > result of the operation that its tested, it is absence of possible > side effects. > > I can put a more elaborate description in the comment to explain this. Indeed, an elaborate description as comments will be great. > >> >>> + { >>> + /* >>> + * Test 32-bit JITs that implement complex ALU64 operations as >>> + * function calls R0 = f(R1, R2), and must re-arrange operands. >>> + */ [...]