rust-lang / rust-lang/rustc_codegen_gcc
-Cllvm-args=-fanalyzer reports uses of uninitialized values
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Description
#[unsafe(no_mangle)]
fn main() {
let _ = Box::new(42);
}
and then compile with -Cllvm-args=-fanalyzer results in
libgccjit.so: warning: : use of uninitialized value 'undefined' [CWE-457] [-Wanalyzer-use-of-uninitialized-value]
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 1
│
│ (1): entry to '_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E'
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 2
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/ub_checks.rs:78:17:
│
└──> '_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 3
│
│libgccjit.so:
│ (3): entry to '_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E'
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 4
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/alloc/layout.rs:138:18:
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 5
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/ub_checks.rs:75:14:
│
<──────┘
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 6
│
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 7
│
│libgccjit.so:
│ (7): use of uninitialized value 'undefined' here
│
libgccjit.so: warning: : use of uninitialized value 'undefined' [CWE-457] [-Wanalyzer-use-of-uninitialized-value]
'_ZN5alloc5alloc15exchange_malloc17h3ccaf01f6c22a3acE': event 1
│
│libgccjit.so:
│ (1): entry to '_ZN5alloc5alloc15exchange_malloc17h3ccaf01f6c22a3acE'
│
'_ZN5alloc5alloc15exchange_malloc17h3ccaf01f6c22a3acE': event 2
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/alloc/src/alloc.rs:351:27:
│
└──> '_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 3
│
│libgccjit.so:
│ (3): entry to '_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E'
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 4
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/ub_checks.rs:78:17:
│
└──> '_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 5
│
│libgccjit.so:
│ (5): entry to '_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E'
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 6
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/alloc/layout.rs:138:18:
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 7
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/ub_checks.rs:75:14:
│
<──────┘
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 8
│
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 9
│
│libgccjit.so:
│ (9): use of uninitialized value 'undefined' here
│
libgccjit.so: warning: : use of uninitialized value 'undefined' [CWE-457] [-Wanalyzer-use-of-uninitialized-value]
'main': event 1
│
│libgccjit.so:
│ (1): entry to 'main'
│
'main': event 2
│
│<source>:3:13:
│ 3 | let _ = Box::new(42);
│ | ^
│ | |
│ | (2) inlined call to '_ZN5alloc5boxed12Box$LT$T$GT$3new17h4d326128f3fc6045E' from 'main'
│
└──> '_ZN5alloc5boxed12Box$LT$T$GT$3new17h4d326128f3fc6045E': event 3
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/alloc/src/boxed.rs:261:16:
│
'_ZN5alloc5alloc15exchange_malloc17h3ccaf01f6c22a3acE': event 4
│
│libgccjit.so:
│ (4): entry to '_ZN5alloc5alloc15exchange_malloc17h3ccaf01f6c22a3acE'
│
'_ZN5alloc5alloc15exchange_malloc17h3ccaf01f6c22a3acE': event 5
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/alloc/src/alloc.rs:351:27:
│
└──> '_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 6
│
│libgccjit.so:
│ (6): entry to '_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E'
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 7
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/ub_checks.rs:78:17:
│
└──> '_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 8
│
│libgccjit.so:
│ (8): entry to '_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E'
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 9
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/alloc/layout.rs:138:18:
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 10
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/ub_checks.rs:75:14:
│
<──────┘
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 11
│
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 12
│
│libgccjit.so:
│ (12): use of uninitialized value 'undefined' here
│
libgccjit.so: warning: : use of uninitialized value 'undefined' [CWE-457] [-Wanalyzer-use-of-uninitialized-value]
'_ZN5alloc5alloc6Global10alloc_impl17h0be00c1c456dfa5cE': events 1-2
/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/alloc/src/alloc.rs:186:9:
'_ZN5alloc5alloc6Global10alloc_impl17h0be00c1c456dfa5cE': event 3
libgccjit.so:
(3): use of uninitialized value 'undefined' here
libgccjit.so: warning: : use of uninitialized value 'undefined' [CWE-457] [-Wanalyzer-use-of-uninitialized-value]
'_ZN63_$LT$alloc..alloc..Global$u20$as$u20$core..alloc..Allocator$GT$8allocate17h69f42b4c603da6acE': event 1
│
│libgccjit.so:
│ (1): entry to '_ZN63_$LT$alloc..alloc..Global$u20$as$u20$core..alloc..Allocator$GT$8allocate17h69f42b4c603da6acE'
│
'_ZN63_$LT$alloc..alloc..Global$u20$as$u20$core..alloc..Allocator$GT$8allocate17h69f42b4c603da6acE': event 2
│
│
└──> '_ZN5alloc5alloc6Global10alloc_impl17h0be00c1c456dfa5cE': event 3
│
│libgccjit.so:
│ (3): entry to '_ZN5alloc5alloc6Global10alloc_impl17h0be00c1c456dfa5cE'
│
'_ZN5alloc5alloc6Global10alloc_impl17h0be00c1c456dfa5cE': events 4-5
│
│
'_ZN5alloc5alloc6Global10alloc_impl17h0be00c1c456dfa5cE': event 6
│
│libgccjit.so:
│ (6): use of uninitialized value 'undefined' here
│
libgccjit.so: warning: : use of uninitialized value 'undefined' [CWE-457] [-Wanalyzer-use-of-uninitialized-value]
'_ZN4core5alloc6layout6Layout13for_value_raw17hfb84ae9010274903E': event 1
│
│libgccjit.so:
│ (1): entry to '_ZN4core5alloc6layout6Layout13for_value_raw17hfb84ae9010274903E'
│
'_ZN4core5alloc6layout6Layout13for_value_raw17hfb84ae9010274903E': event 2
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/alloc/layout.rs:224:18:
│
└──> '_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 3
│
│libgccjit.so:
│ (3): entry to '_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E'
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 4
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/ub_checks.rs:78:17:
│
└──> '_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 5
│
│libgccjit.so:
│ (5): entry to '_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E'
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 6
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/alloc/layout.rs:138:18:
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 7
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/ub_checks.rs:75:14:
│
<──────┘
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 8
│
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 9
│
│libgccjit.so:
│ (9): use of uninitialized value 'undefined' here
│
libgccjit.so: warning: : use of uninitialized value 'undefined' [CWE-457] [-Wanalyzer-use-of-uninitialized-value]
'_ZN72_$LT$alloc..boxed..Box$LT$T$C$A$GT$$u20$as$u20$core..ops..drop..Drop$GT$4drop17h7863c2941af28a7cE': event 1
│
│libgccjit.so:
│ (1): entry to '_ZN72_$LT$alloc..boxed..Box$LT$T$C$A$GT$$u20$as$u20$core..ops..drop..Drop$GT$4drop17h7863c2941af28a7cE'
│
'_ZN72_$LT$alloc..boxed..Box$LT$T$C$A$GT$$u20$as$u20$core..ops..drop..Drop$GT$4drop17h7863c2941af28a7cE': event 2
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/alloc/src/boxed.rs:1652:26:
│
└──> '_ZN4core5alloc6layout6Layout13for_value_raw17hfb84ae9010274903E': event 3
│
│libgccjit.so:
│ (3): entry to '_ZN4core5alloc6layout6Layout13for_value_raw17hfb84ae9010274903E'
│
'_ZN4core5alloc6layout6Layout13for_value_raw17hfb84ae9010274903E': event 4
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/alloc/layout.rs:224:18:
│
└──> '_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 5
│
│libgccjit.so:
│ (5): entry to '_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E'
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 6
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/ub_checks.rs:78:17:
│
└──> '_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 7
│
│libgccjit.so:
│ (7): entry to '_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E'
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 8
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/alloc/layout.rs:138:18:
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 9
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/ub_checks.rs:75:14:
│
<──────┘
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 10
│
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 11
│
│libgccjit.so:
│ (11): use of uninitialized value 'undefined' here
│
libgccjit.so: warning: : use of uninitialized value 'undefined' [CWE-457] [-Wanalyzer-use-of-uninitialized-value]
'_ZN4core3ptr49drop_in_place$LT$alloc..boxed..Box$LT$i32$GT$$GT$17h2d9920e239d4edd1E': event 1
│
│libgccjit.so:
│ (1): entry to '_ZN4core3ptr49drop_in_place$LT$alloc..boxed..Box$LT$i32$GT$$GT$17h2d9920e239d4edd1E'
│
'_ZN4core3ptr49drop_in_place$LT$alloc..boxed..Box$LT$i32$GT$$GT$17h2d9920e239d4edd1E': event 2
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/ptr/mod.rs:804:1:
│
└──> '_ZN72_$LT$alloc..boxed..Box$LT$T$C$A$GT$$u20$as$u20$core..ops..drop..Drop$GT$4drop17h7863c2941af28a7cE': event 3
│
│libgccjit.so:
│ (3): entry to '_ZN72_$LT$alloc..boxed..Box$LT$T$C$A$GT$$u20$as$u20$core..ops..drop..Drop$GT$4drop17h7863c2941af28a7cE'
│
'_ZN72_$LT$alloc..boxed..Box$LT$T$C$A$GT$$u20$as$u20$core..ops..drop..Drop$GT$4drop17h7863c2941af28a7cE': event 4
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/alloc/src/boxed.rs:1652:26:
│
└──> '_ZN4core5alloc6layout6Layout13for_value_raw17hfb84ae9010274903E': event 5
│
│libgccjit.so:
│ (5): entry to '_ZN4core5alloc6layout6Layout13for_value_raw17hfb84ae9010274903E'
│
'_ZN4core5alloc6layout6Layout13for_value_raw17hfb84ae9010274903E': event 6
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/alloc/layout.rs:224:18:
│
└──> '_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 7
│
│libgccjit.so:
│ (7): entry to '_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E'
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 8
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/ub_checks.rs:78:17:
│
└──> '_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 9
│
│libgccjit.so:
│ (9): entry to '_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E'
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 10
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/alloc/layout.rs:138:18:
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked18precondition_check17h7567f7e907a542e2E': event 11
│
│/root/build-rustc-cg-gcc/rustc_codegen_gcc/build/build_sysroot/sysroot_src/library/core/src/ub_checks.rs:75:14:
│
<──────┘
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 12
│
│
'_ZN4core5alloc6layout6Layout25from_size_align_unchecked17h70ce6625d1a2bfa4E': event 13
│
│libgccjit.so:
│ (13): use of uninitialized value 'undefined' here
│
simple true UB things like
#[unsafe(no_mangle)]
fn main() {
unsafe { *core::ptr::null_mut() = 42; }
}
are correctly reported with -Cllvm-args=-fanalyzer -O though, so -fanalyzer is not completely broken:
libgccjit.so: <source>:3:14: warning: : dereference of NULL '0B' [CWE-476] [-Wanalyzer-null-dereference]
'main': event 1
<source>:3:14:
3 | unsafe { *core::ptr::null_mut() = 42; }
| ^
| |
| (1) ⚠️ dereference of NULL '0B'
but something like
#[unsafe(no_mangle)]
fn main() {
let x = 42;
let bad_box = unsafe { std::mem::transmute::<&i32, Box<i32>>(&x) };
drop(bad_box);
}
doesn't get any errors with -Cllvm-args=-fanalyzer -O (likely because __rust_dealloc is not recognized as free function by GCC, while without -O it produces the same warnings about uninitialized values.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Reproduce the warning with the shown Box::new(42) program and -Cllvm-args=-fanalyzer, then trace the reported paths through the rustc_codegen_gcc build sysroot files, including core/src/alloc/layout.rs, core/src/ub_checks.rs, alloc/src/alloc.rs, and alloc/src/boxed.rs. Done means the reproduction no longer reports these uninitialized-value warnings, with appropriate coverage for the affected allocation and layout paths.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 35/100