Optimization of control transfers to dynamically loaded modules

• US 20030079215A1
• Filed: 10/18/2001
• Published: 04/24/2003
• Est. Priority Date: 10/18/2001
• Status: Active Grant

• Current Assignee: Valtrus Innovations Limited (f/k/a Dolya Holdco 9 Limited) (Key Patent Innovations Limited)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Ramasamy, Vinodha, Hundt, Robert, Lofgren, Tom
• Granted Patent: US 6,934,943 B2
• Time in Patent Office: Days
• US Class Current: 717/164
• CPC Class Codes: G06F 9/44521 Dynamic linking or loading; Link editing at or after load time, e.g. Java class loading

Abstract

Method and apparatus for optimization of an executable program that calls procedures in a shared library. Code segments that read procedure address information from a linkage table are first identified. Each linkage code segment is associated with a call to a procedure in the shared library, and the address information in the linkage table is associated with the procedures in the shared library. During program execution, the address information is read from the linkage table and substitute code segments are generated for the linkage code segments. Each substitute code segment has direct loads of the address information for calling the associated procedure instead of the original references to the linkage table. Thereafter, the substitute code segments are executed instead of the linkage code segments.

Claims

1. A computer-implemented method for optimization of an executable program that calls procedures in a shared library, comprising:

identifying linkage code segments in the executable program, wherein each linkage code segment is associated with a call to a procedure in the shared library, reads procedure address information from a linkage table, and transfers control to an associated one of the procedures;

reading the address information from the linkage table;

generating respective substitute code segments for the linkage code segments, each substitute code segment having references to the linkage table replaced by direct loads of the address information without reference to the linkage table; and

executing the substitute code segments instead of the linkage code segments.

2. The method of claim 1, further comprising:

allocating relocation address space for the executable program;

storing the substitute code segments in the relocation address space.

3. The method of claim 1, further comprising for each calling procedure that calls a called procedure in the shared library:

identifying registers that are not used by the calling procedure;

generating in a substitute code segment instructions that store in the registers the address information read from the linkage table.

4. The method of claim 1, further comprising:

annotating linkage code segments in the executable program during compilation;

placing breakpoints at locations of the linkage code segments as indicated by the annotations; and

upon encountering a breakpoint at a linkage code segment, generating a substitute linkage code segment.

5. The method of claim 4, further comprising:

identifying in the annotations registers that are not used by a calling procedure that calls a called procedure in the shared library; and

generating in a substitute code segment instructions that store in the registers indicated by the annotations the address information read from the linkage table.

6. The method of claim 1, wherein the executable program includes a calling procedure that calls a first procedure and a second procedure in a first shared library and calls a third procedure in a second shared library, further comprising:

identifying a set of registers that are not used by the calling procedure;

generating in a substitute code segment instructions that store in the registers in the set the address information read from the linkage table

configuring a substitute code segment associated with the first procedure to load the address information from one of the registers in the set into a branch register prior to transferring control to the first procedure; and

eliminating from a substitute code segment associated with the second procedure, an instruction that loads the address information into the one of the registers if the second procedure is called after the first procedure and before the third procedure.

7. The method of claim 1, wherein the executable program includes a call to a first procedure in a first shared library that calls a second procedure in a second shared library, further comprising in the substitute code segment associated with the call by the first procedure to the second procedure, replacing an indirect branch instruction that targets the second procedure with an instruction-pointer relative branch instruction that targets the second procedure.

8. The method of claim 1, further comprising:

placing breakpoints at procedure entry points;

upon encountering a breakpoint at the entry point of a procedure during program execution, searching for linkage code segments in the procedure, generating substitute linkage code segments for those identified in the procedure, and continuing with execution of the procedure.

9. The method of claim 8, further comprising:

allocating relocation address space for the executable program;

storing the substitute code segments in the relocation address space.

10. The method of claim 8, further comprising for each calling procedure that calls a called procedure in the shared library:

identifying registers that are not used by the calling procedure;

generating in a substitute code segment instructions that store in the registers the address information read from the linkage table.

11. The method of claim 8, wherein the executable program includes a call to a first procedure in a first shared library that calls a second procedure in a second shared library, further comprising in the substitute code segment associated with the call by the first procedure to the second procedure, replacing an indirect branch instruction that targets the second procedure with an instruction-pointer relative branch instruction that targets the second procedure.

12. An apparatus for optimization of an executable program that calls procedures in a shared library, comprising:

means for identifying linkage code segments in the executable program, wherein each linkage code segment is associated with a call to a procedure in the shared library, reads procedure address information from a linkage table, and transfers control to an associated one of the procedures;

means for reading the address information from the linkage table;

means for generating respective substitute code segments for the linkage code segments, each substitute code segment having references to the linkage table replaced by direct loads of the address information without reference to the linkage table; and

means for executing the substitute code segments instead of the linkage code segments.