When doing module and division, first cast to unsigned 32 bit then promote to 64 bit #731
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…omote to 64 bit Signed-off-by: Alan Jowett <[email protected]>
WalkthroughThe pull request introduces modifications to the Changes
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- src/crab/split_dbm.cpp (1 hunks)
- src/test/test_yaml.cpp (1 hunks)
- test-data/muldiv.yaml (1 hunks)
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🔇 Additional comments (4)
test-data/muldiv.yaml (2)
4-16: LGTM: 32-bit division test case is correct and comprehensive.This test case effectively verifies the behavior of 32-bit unsigned division with a negative divisor. The expected result (1) matches the actual result of the operation, demonstrating correct handling of unsigned division in 32-bit context.
19-30: LGTM: 32-bit modulo test case is accurate and well-defined.This test case successfully validates the behavior of 32-bit unsigned modulo operation with a negative divisor. The expected result (97779712) aligns with the actual outcome of the operation, demonstrating proper handling of unsigned modulo in 32-bit context.
src/test/test_yaml.cpp (1)
35-35: LGTM! New test case added correctly.The addition of
YAML_CASE("test-data/muldiv.yaml")is consistent with the existing structure and follows the correct pattern. This new test case aligns with the PR objectives, focusing on unsigned division and modulo operations.Let's verify the existence of the new test file:
src/crab/split_dbm.cpp (1)
1011-1022: Request Verification of Immediate Value Casting RulesTo ensure compliance with the BPF ISA specification, please verify whether the immediate value for 64-bit unsigned division and modulo operations should be treated as a signed 32-bit integer (
int32_t) or an unsigned 32-bit integer (uint32_t). The current implementation casts toint32_twhenfinite_widthis 64, which may not align with the specification if the immediate should be unsigned.Run the following script to check for any inconsistencies in the immediate value casting within the codebase:
Also applies to: 1024-1034
Signed-off-by: Alan Jowett <[email protected]>
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Learnt from: Alan-Jowett PR: vbpf/ebpf-verifier#731 File: src/crab/split_dbm.cpp:1024-1034 Timestamp: 2024-10-15T16:40:13.215Z Learning: In the BPF ISA specification, for 64-bit unsigned modulo operations, the immediate value is treated as a 32-bit signed integer, so casting to `int32_t` is correct.Learnt from: Alan-Jowett PR: vbpf/ebpf-verifier#731 File: src/crab/split_dbm.cpp:1011-1022 Timestamp: 2024-10-15T16:41:02.868Z Learning: In the BPF ISA specification, for 64-bit unsigned division operations, the immediate value is sign-extended from 32 bits to 64 bits and then interpreted as a 64-bit unsigned value, so casting to `int32_t` is correct.src/crab/split_dbm.cpp (2)
Learnt from: Alan-Jowett PR: vbpf/ebpf-verifier#731 File: src/crab/split_dbm.cpp:1024-1034 Timestamp: 2024-10-15T16:40:13.215Z Learning: In the BPF ISA specification, for 64-bit unsigned modulo operations, the immediate value is treated as a 32-bit signed integer, so casting to `int32_t` is correct.Learnt from: Alan-Jowett PR: vbpf/ebpf-verifier#731 File: src/crab/split_dbm.cpp:1011-1022 Timestamp: 2024-10-15T16:41:02.868Z Learning: In the BPF ISA specification, for 64-bit unsigned division operations, the immediate value is sign-extended from 32 bits to 64 bits and then interpreted as a 64-bit unsigned value, so casting to `int32_t` is correct.
🔇 Additional comments (3)
src/crab/split_dbm.cpp (3)
1001-1012: Correct handling of immediate values for unsigned division and moduloThe function
read_imm_for_udiv_or_umodcorrectly implements the casting of immediate values for unsigned division and modulo operations according to the BPF ISA specification. By casting touint32_tfor 32-bit width and toint32_tfor 64-bit width, it ensures that immediate values are interpreted correctly, including proper sign extension for 64-bit operations.
1014-1025: Correct handling of immediate values for signed division and moduloThe function
read_imm_for_sdiv_or_smodappropriately handles immediate values for signed division and modulo operations in line with the BPF ISA specification. Casting toint32_tfor 32-bit width and toint64_tfor 64-bit width ensures that immediate values are correctly sign-extended and interpreted as signed integers of the appropriate width.
1036-1039: Appropriate use of helper functions in arithmetic operationsIn the
applymethod, the updated cases forSDIV,UDIV,SREM, andUREMcorrectly utilize the helper functionsread_imm_for_sdiv_or_smodandread_imm_for_udiv_or_umodto handle immediate values appropriately, ensuring compliance with the BPF ISA specification.
Signed-off-by: Elazar Gershuni <[email protected]>
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- src/crab/split_dbm.cpp (11 hunks)
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src/crab/split_dbm.cpp (1)
Learnt from: Alan-Jowett PR: vbpf/ebpf-verifier#731 File: src/crab/split_dbm.cpp:1005-1012 Timestamp: 2024-10-15T18:33:28.643Z Learning: In `src/crab/split_dbm.cpp`, the functions `read_imm_for_udiv_or_umod` and `read_imm_for_sdiv_or_smod` are intentionally kept separate to clarify the differences between unsigned and signed division and modulo operations.
🔇 Additional comments (4)
src/crab/split_dbm.cpp (4)
1006-1012:read_imm_for_udiv_or_umodandread_imm_for_sdiv_or_smodcorrectly handle immediate values per BPF ISA specificationThe implementation of
read_imm_for_udiv_or_umodandread_imm_for_sdiv_or_smodaccurately reflects the BPF ISA specification for handling immediate values in unsigned and signed division and modulo operations. Keeping these functions separate enhances code clarity by explicitly distinguishing between the different treatments of immediate values based on operation type and bit width.Also applies to: 1014-1024
1034-1036: Ensure correct construction oflinear_expression_tfor multiplicationIn the
MULcase of theapplymethod, the line:assign(x, linear_expression_t(k, y));It's important to verify that
linear_expression_tis correctly constructed to represent the expressiony * k. Ensure that the constructorlinear_expression_t(k, y)properly initializes the linear expression for multiplication, as this may not be immediately clear and could lead to incorrect behavior ifkandyare misinterpreted.
983-984: Consistent handling of finite widths in arithmetic operationsThe methods
applyfor both variable and immediate operations acceptfinite_widthas a parameter. Ensure that thefinite_widthis consistently used within these methods when calling functions likeget_interval,SDiv,UDiv, etc., to correctly handle operations according to the specified bit widths and to prevent unintended behavior due to width mismatches.Also applies to: 1026-1027
15-15: 🛠️ Refactor suggestionConsider passing
variable_tand fundamental types by const referenceSeveral functions are updated to pass
variable_tand fundamental types likeintby value with aconstqualifier. For non-trivial types likevariable_t, passing byconstreference (i.e.,const variable_t&) can avoid unnecessary copying and improve performance. For fundamental types likeint, passing by value is acceptable and efficient, and theconstqualifier can be omitted as it doesn't affect the function signature.Also applies to: 743-743, 926-926, 950-950, 983-984, 1026-1027, 1223-1223, 1233-1233, 1309-1309, 1336-1336
⛔ Skipped due to learnings
Learnt from: elazarg PR: vbpf/ebpf-verifier#689 File: src/crab/split_dbm.cpp:910-910 Timestamp: 2024-09-26T00:57:58.072Z Learning: Avoid suggesting changes that are unrelated to the current PR.
Resolves: #730
This pull request includes changes to handle different bit-widths for unsigned division and modulo operations in the
SplitDBMclass, and adds new test cases to verify these changes.Enhancements to arithmetic operations:
src/crab/split_dbm.cpp: Modified the handling ofUDIVandUREMoperations to correctly cast the immediate value based on the bit-width (32-bit or 64-bit) as specified in the BPF ISA specification.Addition of new test cases:
src/test/test_yaml.cpp: Added a new YAML test case filemuldiv.yamlto the test suite.test-data/muldiv.yaml: Created a new test file with cases for 32-bit and 64-bit unsigned division and modulo operations to ensure correct behavior with negative divisors.Summary by CodeRabbit
New Features
Bug Fixes
Documentation