Run-time identification of dependencies during dynamic linking

Patent metadata

Field	Value
Publication number	US-11340914-B2
Application number	US-202017076485-A
Country	US
Kind code	B2
Filing date	Oct 21, 2020
Priority date	Oct 21, 2020
Publication date	May 24, 2022
Grant date	May 24, 2022

Abstract

Run-time identification of dependencies during dynamic linking. A dynamic linker accesses contents of a first executable file that is to be executed. The dynamic linker, based on the contents of the first executable file, determines that the first executable file includes a first dynamic dependency function configured to be executed by the dynamic linker. The dynamic linker invokes the first dynamic dependency function of the first executable file. The dynamic linker receives, from the first dynamic dependency function, a first run-time dependency identifier that identifies a first run-time dependency, and adds the first run-time dependency identifier to a dependency identifier list.

First claim

What is claimed is:

1. A method comprising:
accessing, by a dynamic linker executing on a computing device comprising a processor device, contents of an executable file that is to be executed;
determining, by the dynamic linker, based on the contents of the executable file, that the executable file includes a first dynamic dependency function configured to be executed by the dynamic linker;
invoking, by the dynamic linker, the first dynamic dependency function of the executable file;
receiving, by the dynamic linker from the first dynamic dependency function, a first run-time dependency identifier that identifies a first run-time dependency; and
adding the first run-time dependency identifier to a dependency identifier list prioritizing dependencies providing a higher symbol-matching priority to map an unresolved symbol in the executable file to the first run-time dependency to override a previously identified run-time dependency in the dependency identifier list.

2. The method of claim 1 wherein the first run-time dependency comprises a shared library.

3. The method of claim 2 wherein the executable file comprises a shared library.

4. The method of claim 3 further comprising:
identifying, by the dynamic linker, an unresolved symbol in the executable file;
identifying, by the dynamic linker, a symbol in the first run-time dependency that matches the unresolved symbol; and
mapping, by the dynamic linker, the unresolved symbol to the symbol in the first run-time dependency.

5. The method of claim 1 wherein determining that the executable file includes the first dynamic dependency function configured to be executed by the dynamic linker comprises identifying, by the dynamic linker, data in the contents of the executable file comprising a dynamic dependency function indicator that indicates the executable file includes the first dynamic dependency function.

6. The method of claim 1 wherein the executable file comprises an Executable Linkable Format (ELF) file.

7. The method of claim 1 further comprising identifying, in an execution environment into which contents of the executable file have been loaded, an address pointer that identifies a location of the first dynamic dependency function.

8. The method of claim 1 further comprising:
obtaining, by the dynamic linker, environment information, the environment information comprising processor device information that identifies characteristics of the processor device; and
providing, by the dynamic linker to the first dynamic dependency function, the environment information.

9. The method of claim 8 wherein the environment information comprises one or more of a process auxiliary vector of the executable file or a process environment vector of the executable file.

10. The method of claim 1 further comprising:
allocating, by the dynamic linker, a first quantity of memory; and
providing, by the dynamic linker to the first dynamic dependency function, a pointer to an initial address of the first quantity of memory.

11. The method of claim 10 wherein receiving, by the dynamic linker from the first dynamic dependency function, the first run-time dependency identifier that identifies the first run-time dependency comprises obtaining, from the first quantity of memory, the first run-time dependency identifier.

12. The method of claim 10 further comprising:
receiving, by the dynamic linker from the first dynamic dependency function, an indication that the first quantity of memory is insufficient;
allocating, by the dynamic linker, a second quantity of memory that is larger than the first quantity of memory; and
providing, by the dynamic linker to the first dynamic dependency function, a pointer to an initial address of the second quantity of memory.

13. The method of claim 1 further comprising:
allocating, by the dynamic linker, a quantity of memory;
obtaining, by the dynamic linker, environment information, the environment information comprising a processor device identifier; and
providing, by the dynamic linker to the first dynamic dependency function, the environment information and a pointer to an initial address of the quantity of memory.

14. The method of claim 1 further comprising:
accessing, by the dynamic linker, a first run-time dependency executable file that corresponds to the first run-time dependency;
determining, by the dynamic linker, based on contents of the first run-time dependency executable file, that the first run-time dependency executable file includes a second dynamic dependency function configured to be executed by the dynamic linker;
invoking, by the dynamic linker, the second dynamic dependency function of the first run-time dependency executable file;
receiving, by the dynamic linker from the second dynamic dependency function, a second run-time dependency identifier that identifies a second run-time dependency; and
adding the second run-time dependency identifier to the dependency identifier list.

15. The method of claim 14 further comprising:
identifying, by the dynamic linker, an unresolved symbol in the executable file;
identifying, by the dynamic linker, a symbol in the second run-time dependency that matches the unresolved symbol; and
mapping, by the dynamic linker, the unresolved symbol to the symbol in the second run-time dependency.

16. The method of claim 14 wherein adding the second run-time dependency identifier to the dependency identifier list further comprises:
adding the second run-time dependency identifier to the dependency identifier list providing a higher symbol-matching priority to the second run-time dependency than the first run-time dependency;
identifying, by the dynamic linker, an unresolved symbol in the executable file, wherein the first run-time dependency and the second run-time dependency each have a symbol that matches the unresolved symbol;
identifying, by the dynamic linker, a symbol in the second run-time dependency that matches the unresolved symbol; and
mapping, by the dynamic linker, the unresolved symbol to the symbol in the second run-time dependency.

17. The method of claim 1 wherein the executable file comprises an ELF file, and wherein determining, by the dynamic linker, based on contents of the executable file, that the executable file includes the first dynamic dependency function configured to be executed by the dynamic linker comprises:
accessing a PT_DYNAMIC element in a program header table of the executable file;
accessing, based on the PT_DYNAMIC element, a dynamic segment of the executable file; and
identifying, in the dynamic segment, a tag that indicates that the executable file includes the first dynamic dependency function configured to be executed by the dynamic linker.

18. The method of claim 1 further comprising:
transferring control, by the dynamic linker to the processor device, to an entry point of the executable file that identifies a first executable instruction of the executable file.

19. A computing device, comprising:
a memory; and
a processor device coupled to the memory to:
access, by a dynamic linker, an executable file that is to be executed;
determine, by the dynamic linker, based on the executable file, that the executable file includes a dynamic dependency function;
invoke, by the dynamic linker, the dynamic dependency function;
receive, by the dynamic linker from the dynamic dependency function, a run-time dependency identifier that identifies a run-time dependency; and
add the run-time dependency identifier to a dependency

Assignees

• Red Hat Inc

Inventors

• Weimer Florian

Classifications

• G06F9/44521 Primary

  Dynamic linking or loading; Link editing at or after load time, e.g. Java class loading · CPC title

• G06F8/433

  Dependency analysis; Data or control flow analysis · CPC title