Module coverage 

The coverage phase: an instrumented test run rendered into web/static/doc/coverage.

grcov can read the raw profiles itself, but it then holds every binary’s results at once and runs one llvm-cov per CPU — about 13 GiB for this workspace, enough to OOM-kill the job on an 8 GiB CI node. So the profiles are merged here single-threaded, each instrumented object is exported to lcov on its own, and grcov only renders. Exporting per object keeps grcov’s numbers: one export over every object discards the counters of functions compiled differently in different binaries.

Unlike grcov, which skips an object llvm-cov cannot export, a failed export fails the phase: every exported object carries a real coverage map, so a failure means a broken build, and a quietly lower percentage would hide it.

Structs

SectionTable 🔒

Where an ELF64 little-endian object keeps its section headers.

Constants

COVMAP_SECTION 🔒

The section every instrumented object carries.

ELF_HEADER_LEN 🔒

ELF_IDENT 🔒

ELF magic, 64-bit class, little-endian data: the only objects CI builds.

E_SHENTSIZE 🔒

E_SHNUM 🔒

E_SHOFF 🔒

E_SHSTRNDX 🔒

LCOV_DIR 🔒

MAX_TABLE_LEN 🔒

Real section and name tables are kilobytes; anything past this is corrupt.

PROFDATA 🔒

PROFRAW_DIR 🔒

SHN_XINDEX 🔒

The name-table index an object with extended numbering stores in section 0.

SH_LINK 🔒

SH_NAME 🔒

SH_OFFSET 🔒

SH_SIZE 🔒

TARGET_DIR 🔒

Functions

collect_objects 🔒

copy_workspace_records 🔒

Copies only the records of sources under root, with their paths made relative. The report ignores every absolute path anyway, and dropping the registry and toolchain records here keeps gigabytes of lcov off the disk. Returns how many records were kept.

elf_has_section 🔒

Looks the name up in the ELF section table. Matching it anywhere in the file also accepts binaries that merely contain the string — xtask itself among them — and llvm-cov refuses to export those.

export_object 🔒

Returns how many workspace source records were kept.

export_objects 🔒

fill 🔒

false when the file ends first: a truncated file is not an object.

has_coverage_map 🔒

instrumented_objects 🔒

instrumented_test_run 🔒

is_candidate 🔒

Executables (tests, binaries, build scripts) and shared objects (proc macros, which run inside rustc) are what carry coverage maps.

le_bytes 🔒

llvm_bin 🔒

llvm-tools installs its binaries beside the host target’s libdir.

llvm_bin_for 🔒

merge_profiles 🔒

One thread: the default of one per CPU took 3 GiB for this merge, one thread takes 250 MiB.

read_region 🔒

Reads len bytes at offset; None when the region is implausibly large or runs past the end of the file.

render_html 🔒

require_llvm_tools 🔒

resolve_extended 🔒

With 0xff00 or more sections the header’s count is 0 and its name index is SHN_XINDEX; the real values live in section 0’s sh_size and sh_link.

run_coverage

Instrumented test run, then the HTML report.

section_name 🔒