GNU C Library (glibc)

You can partition a single input file into multiple distinct benchmark groups using the ##name: directive. This is useful for measuring different input domains (like different bit-precisions in math functions) separately.

Partitioning by Domain

Use ##name: <label> to start a new section. All inputs following the directive belong to that label until the next ##name: directive or the end of the file. Each group is output separately in benchtests/bench.out.

Workload Traces

To measure latency or throughput of a real-world workload trace, use the ##name: workload-<name> directive. In this mode, the entire trace is iterated over multiple times rather than repeating every individual input multiple times.

A libm-test-ulps file is used to define maximal error constraints in Units of Least Precision (ULP). If a function's error exceeds these values, the test fails.

Syntax and Keywords

Specify the function name followed by the allowed error for each floating-point type. Supported keywords are float, double, ldouble, and float128.

Function "yn":
float: 2
double: 6

Testing Different Rounding Modes

By default, tests use FE_TONEAREST. To test other rounding modes, prepend the function name with an underscore and the mode name:

• _downward (FE_DOWNWARD)
• _towardzero (FE_TOWARDZERO)
• _upward (FE_UPWARD)

Example for FE_DOWNWARD:

Function "yn_downward":
float: 3
double: 7

The Hesiod NSS module provides access to Hesiod name service data for the group, passwd, and services databases.

Limitations:

• You cannot iterate over the entire database using getgrent(), getpwent(), or getservent().
• It does not support looking up services by port; it only supports looking up services by name.

Supported Lookups: Because of these limitations, the Hesiod name service is only consulted when using the following functions (or their reentrant counterparts):

• getgrname(), getgrgid()
• getpwname(), getpwuid()
• getservbyname()

When working with Linux kernels, this version of the GNU C Library has the following requirements:

• Kernel Version: Requires Linux kernel version 3.2 or later.
• Dependencies: The shared version of the libgcc_s library must be installed for the pthread library to function correctly.

Security advisories in the advisories directory use a git commit log format consisting of a heading and a free-format description. Key information is extracted using specific tags.

References to code changes follow the pattern: Tag-name: <commit-ref> (release-version)

Where:

• <commit-ref> is the specific git commit.
• release-version is derived from git-describe (e.g., 2.34-NNN). If the -NNN suffix is absent, the change is in the release tarball. If present, the change is on the release/2.YY/master branch and not in a released tarball.

The Tunables framework allows glibc modules to register variables that can be modified via environment variables at runtime. This enables application authors and distribution maintainers to adjust library behavior to match specific workloads without recompiling.

Tunables are organized into a hierarchical namespace structure: TOP_NAMESPACE (defaults to glibc) -> NAMESPACE -> TUNABLE.

Key Constraints:

• The tunable list becomes read-only after the dynamic linker relocates itself. Therefore, setting tunable values is generally limited to the dynamic linker itself and must occur before relocation.

In glibc, the _res symbol is redefined as a macro to provide access to a per-thread resolver state when the program is linked with -lpthread.

This mechanism allows different threads to maintain their own DNS configuration and state without interfering with each other. This is the same pattern used for errno. This per-thread state is also utilized by the gethostby* family of functions to ensure thread safety (e.g., gethostbyname_r).

Warning for Multi-threaded programs: If you manipulate the _res structure in threads other than the "main" thread, calls to traditional (non-n prefixed) functions like gethostbyname will not be influenced by those changes, as they still reference the main thread's state.