Methods, computer program products, and apparatus for initializing global registers6026242Abstract A system, method and computer program product for compiling a source file and to generate a data structure associating a global symbol with a global register referenced in the source file. The data structure enables a linker to initialize the global registers. The compiler also generates an object file from the source file. The object file includes the global register information. A linker links the object file potentially with at least one other object file or shared library to thereby generate an executable file or shared library. The linker uses the global symbol information contained in the object file to initialize the global registers and to perform relocation operations. Claims What is claimed is: Description BACKGROUND OF THE INVENTION
TABLE A
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Matrix of Legal Combinations of Usage of a Given Register
Name Type Attributes
______________________________________
.rela SHT.sub.-- RELA
None
______________________________________
.rela sh.sub.-- link contains the section header index of the associated symbol table; and sh.sub.-- info is 0, indicating that this section only contains register relocations. The object file 106, as well as zero or more other object files 108, and/or zero or more shared libraries 110 are transferred to a static linker 114, according to one embodiment of the present invention. The other object files 108 were previously compiled by the compiler 104 of the present invention and the shared libraries 110 were previously created by the static linker 114. The static linker 114 generates an executable file 116 or shared library. According to one embodiment of the present invention, the static linker 114 generates another shared library. As will be appreciated, a shared library is a form of an object file. Accordingly, the terms "object file" and "shared library" will be used interchangeably herein. As will be appreciated by persons skilled in the art, the executable file 116 includes code, data, and other information from the object files 106, 108, and also contains references to shared libraries 110 (i.e., code, data, etc. from the shared libraries 110 are not actually embedded in the executable file 204). During run-time, the executable file 116 and the shared libraries 110 are transferred to a run-time linker 118. The run-time linker 118 resolves references contained in the executable file 116 to the shared libraries 110, initializes the global registers with global register initialization engine 119, and produces an execution image 120. The execution image 120 is stored in main memory 208 and executed by a central processing unit 204 (FIG. 2). Generally speaking, the operation of the static linker 114 and run-time linker 118 may be broken down into four phases, as discussed in detail below. FIG. 2 is a block diagram of a computer system 202 according to a preferred embodiment of the present invention. The computer system 202 includes one or more processors, such as central processing unit (CPU) 204, connected to a communication medium, such as a bus 206. The computer system 202 further includes a main memory (e.g., without limitation a random access memory (RAM)) 208, which is also connected to the bus 206. The computer system 202 further includes a compiler 104 and first and second linkers including a static linker 114 and a run-time linker 118, which are stored in the main memory 208 according to one embodiment. In particular, the source file 102; the object files 106 and 108; the shared libraries 110; and the execution image 120 are also preferably stored in the main memory 208. Computer system 202 further includes registers a plurality of registers 210 including one or more global registers. According to one embodiment of the present invention, a computer program product (such as disk 214) includes a computer readable media having computer program logic recorded thereon, according to the present invention. In particular, the computer logic is executed in the computer system 202 to enable the computer system 202 to perform the functions of the present invention. The computer log is read by a floppy drive 212 for example. The computer program logic, which represents the compiler 104 and the linkers including static linker 114 and run-time linker 118, may then be loaded into the main memory 208 (as shown), and executed by the CPU 204. A suitable form for the computer system 202 is a Sun Microsystems workstation made by Sun Microsystems, Inc., of Mountain View, Calif. Any other suitable computer system could alternatively be used. FIG. 3A is a flowchart of a linker process which can be used in connection with the present invention. Referring to a flowchart 302 shown in FIG. 3A, the static linker 114 performs a read phase 306, a layout phase 308, a relocation phase 310, and a write phase 312. These linker phases 306, 308, 310, and 312 are performed in connection with the present invention. FIG. 3B is a flowchart of a linker process according to one embodiment of the present invention which includes initialization of global registers. In particular, referring to a flowchart 302 shown in FIG. 3B, the run-time linker 118 performs a read phase 306, a layout phase 308, a relocation phase 310, a write to memory phase 312, an initialization of global registers phase 364 according to the present invention, and a give control to the executable file phase 366, followed by a termination or end of execution state 369. FIG. 3C is a flow chart of global register initialization according to the present invention. In particular, FIG. 3C shows an initialization process 382 according to one embodiment of the present invention. Initialization includes reading 386 initialization information from a data structure according to the present invention, which contains initialization information for predetermined global registers. According to one embodiment of the present invention, the data structure is a symbol table. According to another embodiment of the present invention, the data structure is a unitary data structure as shown in the related application entitled "Unitary Data Structure Systems, Methods, and Computer Products, for Global Conflict Determination," which is expressly incorporated herein in its entirety by reference. Initialization additionally includes processing 388 of the initialization information which has been read, using the global register initialization engine (GRIE) according to the present invention. Further, initialization includes writing 390 the processed initialization information into predetermined global registers. Finally, initialization is completed 394. FIG. 4A is a block diagram of an object file produced by a compiler according to a preferred embodiment of the present invention, in which object files are produced by the compiler with a global register data structure (GRDS) 406 to enable determination of conflicts between global register assignments by the static and run-time linkers. As shown in FIG. 4A, the object file 106 includes code and data 402, a symbol table 404, a relocation table 412, and GRDS 406 according to the present invention. The manner in which the compiler 104 generates such code and data 402, the symbol table 404, and the relocation table 412, will be apparent to persons skilled in the relevant art. In accordance with the present invention, the compiler 104 does not identify global symbol conflicts, or perform relocations. Instead, the compiler 104 generates global symbol and global register information, and embeds such information in a global register data structure (GRDS) 406 which in turn is contained in the object file 106. Such global symbol and global register information includes information about global symbols and global registers defined and/or referenced in the source file 102, and includes additional information on how such global symbols and global registers are used by the source file 102. The global symbol and global register information 406 generated by the compiler 104 enables the linker 112 to identify global symbol conflicts and global register conflicts and to perform relocations to associate symbols with memory locations and global registers, as the case may be. The global register data structure (GRDS) 406 is further described below. FIG. 4B is a block diagram of a GRDS 406 according to one embodiment of the present invention, including usage information (UI) 440 and initialization information(II) 441, to enable determination of conflicts between global register assignments by the static and run-time linkers. GRDS 406 communicates with global register initialization engine (GRIE) 119 to enable global register initialization with initialization information 441 according to the present invention. FIG. 4C is a block diagram of the protocol for UI 440 in GRDS 406 according to the present invention. In particular, the UI protocol includes a global register number (GRN) 450 and global symbol information (GSI) 451. FIG. 4D is a block diagram of the protocol for II 441 in a GRDS 406 according to the present invention. In particular, the II 441 includes an initial value (IV) for each global register, as well as flags 461 to provide an initializer presence indication 471 and an indication of the absence of a name 472. As discussed above, the compiler 104 does not identify global symbol conflicts or perform relocations. Instead, identification of global symbol conflicts is delayed from compile time to link time. In step 506 of FIG. 5, the compiler 104 generates information about global symbols and how they are used. Such information is called symbol information 406, and is embedded in the object file 106 produced by the compiler 104. FIG. 5 is a flowchart of a compilation/linking process according to a preferred embodiment of the present invention. In particular, FIG. 5 depicts a flowchart 502 according to the present invention which represents the high-level operation of the compiler 104 and the applicable one of linkers 114, 118. The compiler 104 performs step 506 when compiling the source file 104, and the applicable one of linkers 114, 118 performs step 508 when processing the object files 106 and 108, and the shared libraries 110. Flowchart 502 begins with step 504, where control passes to step 506. The compiler generates global symbol table entries to indicate how the containing object file uses the application-reserved global registers. The programmer indicates to the compiler by flags, for example, according to one embodiment of the present invention, or to the assembler by flags or directives according to one embodiment of the present invention, what the global register usage is. In step 506, the compiler 104 generates an object file 106 from the source file 102. In step 508, the applicable one of linkers 114, 118 generates an executable file 116, and then an execution image 120 from the object files 106 and 108, and the shared libraries 110. As discussed above, during the generation of the executable file 116 and the execution image 120, the static linker 114 and the run-time linker 118 perform a read phase 306, a layout phase 308, a relocation phase 310, and a write phase 312. According to the present invention, these linker phases 306, 308, 310, and 312 are modified such that the static linker 114 and the run-time linker 118 identify global symbol conflicts and perform relocations. The operation of the static linker 114 and the run-time linker 118 is further discussed below. After step 508 is fully performed, the operation of flowchart 502 is complete, as indicated by step 510. The static linker checks these symbol table entries in all the object files being combined into an executable file or shared library to ensure that the global registers are used compatibly. The resulting object includes, according to the present invention, entries in its symbol table to indicate the resulting object's global register usage. The static linker warns if any shared library that was referenced during the linking uses global registers in a fashion incompatible with the object being built. Further according to the present invention, the static linker generates a warning if a shared object is being built that uses application-reserved global registers. The dynamic linker according to the present invention checks that all object files being bound into the target process have compatible uses of the application-reserved global registers. A dlopen() of an object that is not compatible with the application process, for example, fails with an error.
TABLE B
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Matrix of Legal Combinations of Usage of a Given Register
Obj1.backslash.Obj2
Unused Scratch Symbol
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Unused OK OK OK
Scratch OK OK NO
Symbol OK NO *
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*OK is used if the symbols are identical; NO is used if they are not identical. Two symbols are identical if and only if one of the following is true: A. They are both global and have the same name. B. They are both local, have the same name, and are defined in the same object. The scratch symbol according to the present invention is treated as a symbol since a null name only matches a null name and scratch registers according to the present invention have global scope. A matrix of legal combinations of st.sub.-- shndx for the same register symbol follows:
TABLE C
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Matrix of Legal Combinations of Initialization of a Given Register
Obj1.backslash.Obj2
UNDEF ABS
______________________________________
UNDEF OK OK
ABS OK NO
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The symbol information 406 includes according to one embodiment of the present invention: 1. a symbol table 408 containing a list of global symbols; and 2. a relocation table 412 containing a list of global symbols. Using the symbol information 406, the linker 114 or 118 as applicable in step 508 determines the exact layout of global symbol used by an application and then satisfies the relocations required. The symbol table 408 comprises a plurality of entries, where each entry corresponds to a symbol. These entries are used by the linkers 114 and 118 during the relocation process. FIG. 6 is a detailed flowchart of link processing according to a preferred embodiment of the present invention. FIG. 6 is a detailed flowchart of a linker which generally can be broken down into four phases: a read phase 306, a layout phase 308, a relocation phase 310, and a write phase 312 as noted above with respect to FIG. 3. According to the present invention, these linker phases 306, 308, 310, and 312 are restructured such that the applicable linker identifies global symbol conflicts based upon information contained in one or more of the unitary data structures (UDSs) 406. Such modifications are shown in a flowchart 602 which is represented in FIG. 6. In particular, step 606 is preferably performed in the read phase 306 in order to merge the global symbol information found in selected objects. Step 608 of the linker operation is preferably performed between the read phase 306 and the layout phase 308, accomplishing the identification of global register conflicts. Steps 612 and 614 are preferably performed between the layout phase 308 and the relocation phase 310 during operation of the applicable linker. Step 616 relates to relocations to modified memory addresses or global registers, and is preferably performed during the relocation phase 310. Flowchart 602 shall now be described in greater detail. Flowchart 602 particularly begins with step 604, where control immediately passes to step 606 to accomplish merger of global symbol information. In step 606, the applicable linker reads in the object files 106, 108 and the shared libraries 110 and merges together the global symbol information 406 contained in the UDS 406. Further, the applicable linker merges together the UDS 406 contained in these files to generate a merged UDS. Similarly, the applicable linker merges together the relocation tables 412 to generate a merged class relocation table. Next in step 608, the applicable linker identifies global symbol conflicts. In particular, the applicable linker processes the merged tables and determines the layout of each symbol (for example, the size and alignment of each symbol, the number of fields, the data types of the fields, the number of bytes from the top of the symbol to each of the fields, etc.). The applicable linker particularly creates a separate data structure for each symbol, and stores this symbol specific information in such separate data structures. These data structures are called "layout data structures" for reference purposes. Upon the completion of step 608, the applicable linker is aware of much of the symbol-related information produced by a compiler. According to step 610, global symbol conflicts are identified. In step 612, the applicable linker evaluates the symbols in the merged UDS. In particular, the applicable linker determines the value of the symbol in each entry of the merged symbol table, and stores this value in the value field of this entry. Consider, for example, the example UDS 406 in FIG. 4B. The applicable linker determines the values of particular entries by referencing an associated layout data structure. The applicable linker stores these values in the value fields of the entries of the UDS 406 which is contained in UI 440 of UDS 406. The manner in which the linker 112 calculates the values of other symbol types is described above. In step 614, the applicable linker initializes global register structures. In particular, during step 614 the applicable linker generates tables and table pointer information tables including UDSs 406, and stores these tables in the appropriate data structures that have been allocated. In step 616, the applicable linker performs the relocations specified in the entries of the merged relocation table. The manner in which the applicable linker performs this function is described above. After step 616 is fully performed, the operation of flowchart 602 is complete, as indicated by step 618. As will be appreciated by persons skilled in the relevant art, the operation of the applicable linker described above is, in practice, collectively performed by the static linker 114 and the run-time linker 118. Whether the operations described above are performed by the static linker 114 or the run-time linker 118 is not important in the present invention. Preferably, however, the static linker 114 attempts to prelink executables and shared objects so that if the executable and shared objects are in the same state as when they were created, then the run-time linker 118 needs to only load the files and start running. In practice, the run-time linker 118 may have to redo many of the relocations that were done by the static linker 114. FIG. 7 is an example of a symbol table generated by a compiler according to a preferred embodiment of the present invention. FIG. 7 particularly shows first and second symbol table entries, 714 and 718, in an example symbol table 408. Each entry in the symbol table 408 includes information that identifies the symbol type, and information that indicates the value of the symbol for this class. Entries for particular symbols may additionally include further fields including for example symbol name, symbol size, symbol binding, and a symbol section index. The symbol name when appropriate contains the name of a member. The list of symbol types is implementation specific, and depends on a number of factors, such as the computer programming language and the target machine. Example symbol types will be apparent to persons skilled in the relevant art. As described below, the applicable linker calculates the values of the symbols in the symbol table 408 according to the present invention before processing the relocation entries in the relocation table 412. In processing each relocation entry, the value is extracted from the symbol table and is stored at the given address according to the type of the relocation entry. Consider the example of FIG. 7. Prior to processing the relocation entries in the relocation table 412, the applicable linker evaluates the symbol entries 714, 718 in the symbol table 408 and reads the value associated with each symbol entry. The applicable linker then inserts the value read into the value field of the symbol entry 714. According to one embodiment of the present invention, the applicable linker inserts this value (8 bytes) into the value field of the symbol entry 718. While processing a particular relocation entry, the applicable linker according to the present invention replaces a placeholder in the instruction at a particular address with the value in symbol entry 714. This may be a case pointer in a relocation entry which points to symbol entry 714. Similarly, while processing a particular relocation entry for relocation table 412, the applicable linker replaces the placeholder, such as a zero (i.e., "o" for example) in the instruction at a particular address with the value provided in symbol entry 714. A register symbol in a symbol table according to one embodiment of the present invention is indicated by a specific additional Symbol Type and Value as set forth below:
TABLE D
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Additional Symbol Table Type
Name Value
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STT.sub.-- REGISTER
13
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A symbol table entry for a register symbol according to one embodiment of the present invention particularly includes the following elements:
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st.sub.-- name
Index into the string table of the name of the
symbol. An index value of 0, which points to the
null name in the string table, indicates that the
register is used for scratch. A scratch register must
have binding STB.sub.-- GLOBAL.
st.sub.-- value
Register number. Register numbers correspond to
the assignments in the SPARC Architecture
Manual for integer registers.
st.sub.-- size
unused (0)
st.sub.-- info
ELF64.sub.-- ST.sub.-- INFO (bind.type)
bind is typically STB.sub.-- GLOBAL, but does reflect
the actual declared scope of the name (that is, it
could be STB.sub.-- WEAK or STB.sub.-- LOCAL).
type must be STT.sub.-- REGISTER (13)
st.sub.-- other
unused (0)
st.sub.-- shndx
SHN.sub.-- ABS if this object initializes this register
symbol; SHN.sub.-- UNDEF otherwise. An initializer
for a SHN.sub.-- ABS register symbol is specified with a
special register relocation type.
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Absence of an entry for a particular global register indicates that that particular global register is not used by the object. An object according to the present invention uses one or more of the application-reserved global registers and indicates this usage with an appropriate symbol-table entry. The following dynamic array tag is moreover added to the symbol table according to one embodiment of the present invention:
TABLE E
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Symbol Table Dynamic Array Tags
Shared
Name Value d.sub.-- un
Executable
Object
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DT.sub.-- REGISTER
0 .times. 7000001
d.sub.-- val
optional optional
DT.sub.-- REGISTER
This element contains the index of an
STT.sub.-- REGISTER symbol. There is one
of these entries for every STT.sub.-- REGISTER
symbol table entry in the symbol table.
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The compiler 104 according to the present invention accordingly generates code that is relocated at link-time. In particular, if a variable is referenced in a source file, the compiler 104 generates both a symbol table 408 and a relocation table 412. According to one embodiment of the present invention, the generation of symbol and relocation tables is accomplished with a specialized global register relocation type which is used to identify global register conflicts and to initialize the global registers prior to execution of the execution image which is produced. FIG. 8 is an example of a relocation table according to one embodiment of the present invention. The relocation table 412 contains a list of the relocations which must be performed by the applicable linker during link-time. Each entry in the relocation table 412 includes a relocation type, an address of either an instruction or a data element that needs to be relocated, and, in all but one case, a pointer to an entry in the symbol table 408. The following relocation type is added to the relocation table according to the present invention:
TABLE F
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Additional Relocation Type
Name Value Field Calculation
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R.sub.-- SPARC.sub.-- REGISTER
54 V-xword64 S + A
R.sub.-- SPARC.sub.-- REGISTER
This relocation type is used to initialize a
register symbol. Its offset member con-
tains the register number to be initialized.
There must be a corresponding register
symbol for this register of type
SHN.sub.-- ABS.
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While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
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