-Cllvm-args=-fanalyzer reports uses of uninitialized values

Reproduce la advertencia con el programa Box::new(42) mostrado y -Cllvm-args=-fanalyzer; después, sigue las rutas indicadas a través de los archivos del sysroot de la compilación de rustc_codegen_gcc, incluidos core/src/alloc/layout.rs, core/src/ub_checks.rs, alloc/src/alloc.rs y alloc/src/boxed.rs. Se considerará terminado cuando la reproducción deje de informar estas advertencias de valores no inicializados y exista una cobertura adecuada para las rutas de asignación y de layout afectadas.

#[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.