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HP UX Software Transition Kit (STK) manual Looking Inside a Compiler, What is an Object File?

Models: UX Software Transition Kit (STK)

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Figure 1 High-level View of the Compiler

Looking Inside a Compiler

On the surface, it appears as though an HP-UX compiler generates an a.out file by itself. Actually, an HP-UX compiler is a driver that calls other commands to create the a.out file. The driver performs different tasks (or phases) for different languages, but two phases are common to all languages:

1.For each source file, the driver calls the language compiler to create an object file. (See also “What is an Object File?” (page 18))

2.The HP-UX linker (ld) links the specified object files to create either a reusable object file, also called a shared library, or an executable, which is named a.out by default unless a name is specified. (See also “Compiler-Linker Interaction” (page 19).)

Figure 2 summarizes how a compiler driver works.

Figure 2 Looking Inside a Compiler

The C, aC++, and Fortran90 compilers provide the -v(verbose) option to display the phases a compiler is performing.

What is an Object File?

An object file is basically a file containing machine language instructions and data in a form that the linker can use to create an executable program. Each routine or data item defined in an object file has a corresponding symbol name by which it is referenced. A symbol generated for a routine

18 Compiling and Linking Programs on HP-UX

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HP UX Software Transition Kit (STK) manual Looking Inside a Compiler, What is an Object File?

Contents

HP-UX Linker and Libraries Users Guide Page Contents Contents Creating and Using Libraries Linker Tools for Itanium-Based SystemsLinker Tools for PA-RISC Systems Contents Shared Library Management Routines 136 Contents Contents Using Mapfiles 191 Writing and Generating Position-Independent Code 185Improving Your Application Performance 202 Glossary 225 Related Information Document conventions and symbolsIntended Audience Document conventionsHP Encourages Your Comments Document OrganizationUsing Mapfiles Improving Your Application PerformanceCompiling Programs on HP-UX An Example OverviewThis chapter addresses the following Compiling Programs on HP-UX An Example What is an Object File? Looking Inside a CompilerGlobal Definitions Compiler-Linker InteractionLocal Definitions External ReferencesCc Entering Link editor Linking Programs on HP-UX Crt0.o Startup FilePrograms Entry Point A.out FileMagic Numbers PA-RISC only Linker uses four startup filesLinking with Libraries 32-bit Mode Magic Number Linker OptionsLibrary Naming Conventions Default Libraries Link Order File PermissionsLibrary Naming Conventions Default LibrariesDefault Library Search Path Link OrderLoading Programs exec Deferred Binding is the DefaultRunning the Program Binding Routines to a ProgramLinker Thread-Safe Features Determining How to Link Programs or Libraries Linker Tasks Using the Compiler to Link Changing the Default Library Search Path with -Wl, -LExample Using -Wl, -L Getting Verbose Output with Passing Linker Options from the Compiler Command with -WlExample Using -Wl Renaming the Output File with -oLinking with the crt0.o Startup File in 32-bit mode PA-RISC Using Linker CommandsSuppressing the Link-Edit Phase with -c Overriding the Default Linker Search Path with LpathUsing $ORIGIN Augmenting the Default Linker Search Path with -LAugmenting the Default Linker Search Path with +origin Nonfatal Shared Library Binding with -B nonfatal Changing the Default Shared Library Binding with -BExample Using -B immediate Restricted Shared Library Binding with -B restrictedLazydirect Shared Library Binding with -B lazydirect Direct Shared Library Binding with -B directShared Library Binding with -B group Shared Library Binding with -B nodeleteComparing -B symbolic with -h and +e Improving Shared Library Performance with -B symbolicExample Using -B symbolic Case 1 Building a Shared Library with -B symbolicOr export the convertrtn symbol Symbol Hidden in a Shared LibraryChoosing Archive or Shared Libraries with -a Option Settings to -aExample Using -a Linking Shared Libraries with -dynamicWhen to use -h versus +e Exporting Symbols with +eExample Using +e Linking Archived Libraries with -nosharedExporting Symbols with +ee Exporting Symbols from main with -EEmitting debug information in a separate file Example Using -h Hiding Symbols from Export with +hideallsymbolsHiding Symbols with -h Tips on Using -hHiding and Exporting Symbols When Building a Shared Library Hiding Symbols when Combining .o Files with the -r OptionHiding and Exporting Symbols when Creating an a.out File Specifying a Path List with +b Not Recording Link Time Paths with +nodefaultrapthMoving Libraries after Linking with +b Syntax of the +b option isPath List Specifying a Path List with +s and Shlibpath Moving Libraries After Linking with +s and ShlibpathIgnoring Dynamic Path Environment Variables with +noenvvar For more information Path ListPassing Linker Options in a file with -c Thereafter, the following commands would be equivalentControlling Archive Library Loading with +noforceload Passing Linker Options with LdoptsExample Using -l Flagging Unsatisfied Symbols with +noallowunsatsUsing the -l option Specifying Libraries with -l and -lUsing the IPF Linker with +compat or +std Using the Linker with +compat for Compatibility ModeControlling Output from the Unwind Table with +strip unwind Using the Linker with +std for Standard Mode Dynamicflag is passed to shlloadChanging Mapfiles with -k and +nodefaultmap Linking in PA-64 Mode with +stdLinking in PA-32 Mode with +compat Selecting Verbose Output with +vtypeAll Allocating Storage for Uninitialized Data with +nobss Turning on the linkage table protection with +protectCreating read-only text segment in Mpas executable Initializing Floating Point Environment with +FPFlags that are supported Turn Off Linker Warnings with -w Options to change various attributes Changing a Programs Attributes with chatr1Linker toolset for Itanium-Based systems LibnameDeferred +as modeImmediate +b flag+md flag Enabledisable+protect disable +memcheckViewing Symbols in an Object file with nm1 Format Viewing the Contents of an Object File with elfdump1 +linkmapfile +linkmap+linkmapbss +objdebugViewing Library Dependencies with ldd1 Symbol resolution problems to stderrSymbol +T num2Example 3 Using the ldd command Listing Dynamic Libraries with pldd1Level with level Printing a Stack Trace with pstack1Options to view information specified files ParameterExample 5 Calling pstack with a process id Example 6 Calling pstack with -level optionLinker Tools for Itanium-Based Systems Viewing the Size of Object File Elements with size1 Reducing Storage Space with strip1Example 9 Calling pstack with special argument Improving Program Start-up with fastbind1 Options to control the amount of information strippedExample 10 Example Tracing Inter-Module Procedure Calls with ltrace1Finding Object Library Ordering Relationships with lorder1 Example 11 Examples$/usr/ccs/bin/ltrace ./a.out -a arg1 arg2 arg3 .. argn Using chatr for 32-bit Program Attributes Using chatr for 64-bit Program Attributes For the 32-bit compatible syntax+si For the 64-bit only syntax+dz +saExample 12 Viewing Symbols in an Object file with nm1 $THISSHORTBSS$To view Optional list of symbol resolution problems to stderr Example 13 Viewing library dependencies with ldd1 To display Example 14 Improving Program Start-up with fastbind1 Before you ran fastbind on it$ ar cr library `lorder *.o tsort` PA-RISC Changes in Hardware Compatibility ELF Object File FormatPA-RISC 2.0 Compatibility PA-RISC Architectures and Their System ModelsVersions of PA-RISC architecture +objdebug mode +nosrcposPA64 Mode Linker Options Linker-Defined SymbolsThis section describes the PA64 mode linker options Symbol names Dynamic Path Searching for Shared LibrariesRunpath Perform 32-bit link Symbol Searching in Dependent Libraries PA-64, IPF 64-bit mode exampleSystem Libraries Locations and Library Name Extension System Library LocationShared Library Extension suffix Statically-bound programs archive-bound programs Creating Libraries on HP-UX Using Libraries on HP-UXOverview of Shared and Archive Libraries Creating Archive Libraries Creating Shared LibrariesWhat are Archive Libraries? Out filesDefault Behavior When Searching for Libraries at Run Time What are Shared Libraries?Dynamic Loader Example Program Comparing Shared and Archive Libraries Running setuid ProgramsTwo Processes Sharing libc Creating Archive Libraries Profiling Shared Libraries with gprof1Contents of an Archive File Overview of Creating an Archive LibraryExample of Creating an Archive Library Replacing or Adding an Object Module Summary of Keys to the ar1 CommandReplacing, Adding, and Deleting an Object Module Deleting an Object ModuleCreating Shared Libraries Using /usr/lib and /usr/lib/pa2064Using /usr/local/lib or /usr/contrib/lib Archive Library Location IPFCreating the Shared Library with ld Example Using +zCreating Position-Independent Code PIC Comparing +z and +ZShared Library Dependencies Order in Which Libraries are Loaded Load GraphPlacing Loaded Libraries in the Search List LibDImproving Shared Library Performance Updating a Shared LibraryShared Library Location IPF Incompatible Changes to a Shared LibraryConsider a case where a.out has the following dependents That is, a.out is built with commands like theseLdpreload Example Symbol resolution order for the user libraries is Ldpreload Example PA-RISCBit Behavior Out -- libA.sl -- libC.sl -- libD.sl -- libB.sl Using Profile-Based Optimization on Shared Libraries Exporting Only the Required SymbolsPlacing Frequently-Called Routines Together Y.o Using the +ESlit/+Olit=all Option to ccMaking Shared Libraries Non-Writable None+condrodata Command-Line Option Using Filtered Shared Libraries 32-bit Mode OnlyBuilding Filtered Shared Libraries Run time behavior of filtered shared libraries InitializersWhen to Use Shared Library Versioning Version Control with Shared LibrariesFunction Level Versioning How to Use Library-Level Versioning Maintaining Old Versions of Library ModulesLibrary-Level Versioning File System Links to Shared Libraries Creating a New, Incompatible Version of the Library+h Option and Internal Names Intra-Library Versioning PA-RISC only Using shlload3X with Library-Level VersioningThen set up the corresponding file system links Version Number Compiler Directive#pragma Hpshlibversion date Shared Library Dependencies and Version ControlAdding New Versions to a Shared Library $SHLIBVERSION dateSwitching from Archive to Shared Libraries Relying on Undocumented Linker BehaviorSpecifying a Version Date Version Control Absolute Virtual AddressesStack Usage Debugger LimitationsUsing the chroot Command with Shared Libraries Summary of HP-UX LibrariesProfiling Limitations Example 1 Unsatisfied Symbols Example 1 Unsatisfied Symbols CompilingExample 1 Unsatisfied Symbols Creating the Executable Example 1 Unsatisfied Symbols Modifying a FunctionExample 2 Using shlload3X Example 1 Unsatisfied Symbols Problem of Unsatisfied SymbolExample 2 Using shlload3X Creating the Executable Example 2 Using shlload3X Rebuilding the Shared Library Example 3 Hidden DefinitionsExample 3 Hidden Definitions Compiling Using Shared Libraries in Default Mode Example 3 Hidden Definitions Modifying a FunctionInternal Name Processing Dthpneeded entryShared Library Symbol Binding Semantics Link-Time Symbol Resolution in Shared LibrariesDynamic Path Searching for Shared Libraries Resolution of Unsatisfied Shared Library References If these files are compiled and linked asPA-32 linker toolset produces Promotion of Uninitialized Global Data Items Symbol Searching in Dependent Libraries Mixed Mode Shared Libraries Search Order of Dependent LibrariesIPF Library Examples Libfile4.soFollowing example builds a standard mode library Library example IPF Dynamic Path SearchingLibrary Example IPF Compatibility Mode Link You can use chatr+s to enable a.out in file1 and file2For the following libraries with dependencies Linking Libraries with +b pathlist Above example, if you type When linking main.o, the link order is 1. ./libbar.so foundLinker issues the following error message InsteadDo not mix use of the shlload and dlopen APIs Shared Library Management Routine SummariesDlopen Routines Summary Dl* routines for shared library managementShlload Routine Summary Related Files and CommandsShared Library Header Files Routines for shared library managementStyles of Initializers Using Shared Libraries with cc and ld OptionsInitializers for Shared Libraries Init/Fini Style InitializersUsing Init/Fini Initializers HP-UX-10.X Style InitializersInit and Fini Usage Example Source for lib1.so file lib1.c lib1 Ordering Within an Executable or Shared Library Finis from any .o files used in my64bit.aOrdering Among Executables and Shared Libraries Using HP-UX 10.X Style Initializers Declaring the Initializer with the +I OptionOrder of Execution of Multiple Initializers Accessing Initializers Addresses Initializer SyntaxExample An Initializer for Each Library Source for testlib.c #include stdio.h #include dl.h main Example a Common Initializer for Multiple Libraries Source for Initializer file init.c #include dl.hFollowing are the commands used to build these libraries Dlopen Routine Following is the command to create the executable testlib2Dlopen Shared Library Management Routines SyntaxReturn Values ParametersDescription Dlopen Shared Library Management Routines Using dlopen to load a shared library Dlsetlibpath Routine SynopsisRtldflagdisablestdpath Rtldflagdisablecwdpath Using dlsetlibpath to set the dynamic search pathDlgetfileinfo Routine ErrorsDlerrno Routine Multithread UsageShared Library Management Routines Dlerror Routine Using dlerror to get diagnostic informationDlsym Routine Usage HandleDesc Dlget RoutineIndex DescsizeUsing dlget to retrieve information about loaded modules Dlmodinfo RoutineUsing dlmodinfo to retrieve information about a load module Dlgetname RoutineDlclose routine closes a shared library Using dlgetname to retrieve pathnameDlclose Routine Int dlclosevoid *handleUsing dlclose to unload a shared library Dladdr routine gets the symbolic information for an addressDladdr Routine Diagnostics Using dladdr to get the symbolic information for an address Following example shows how to use dladdr toDlmodadd Routine Dlmodremove removes information registered using dlmodadd Dlmodremove RoutineDlgetmodinfo Routine Using dlgetmodinfo Following example shows how to use dlgetmodinfoParameters Shlload Shared Library Management RoutinesShlload Routine Shlload routine explicitly loads a libraryEnomem Shlload Usage Shlload ExampleLoadlib Function to Load a Shared Library Bindfirst Modifier Bindnonfatal ModifierBindverbose Modifier Dynamicpath ModifierBindtogether Modifier LibG together and correctly resolves all symbolsShlfindsym Routine Bindbreadthfirst ModifierShlfindsym&handle,foo Shlt handleHandle = Null Same as TypedataShlfindsym Example Shlget and shlgetr Routines IndexExample Shlgethandle and shlgethandler Routines Shldefinesym RoutineShlgetsymbols Routine Typeprocedure Members of the shlsymbol structure are defined as follows Shlsymbol StructureShowsymbols Display Shared Library Symbols Example 17 shlgetsymbols ExampleShowall Use showsymbols to Show All Symbols Showall program shown above was compiled with the commandOutput produced by running this program is shown below Shlunload Routine FpumodelstorageUnsupported Shared Library Management Flags Dynamic Loader Compatibility WarningsUnsupported Shared Library Management Routines Shlunload Routine Returning EtxtbsyTypeprocedure Typedata Typestorage What is a Relocatable Object Code? What is a Absolute Object Code?What is a Position-Independent Code? Generating Position-Independent CodePIC Requirements for Compilers and Assembly Code Assigned Goto Statements Long Branches and Switch TablesLong Calls Literal ReferencesProcedure Labels Global and Static Variable ReferencesWriting and Generating Position-Independent Code Changing Mapfiles with -k filename and +nodefaultmap Mapfile Example Using -k mapfile and +nodefaultmapControlling Mapfiles with the -k Option Using Mapfiles Simple Mapfile Default HP-UX 11.0 Release MapfileIPF 32-bit linker uses the following default mapfile Following directives show how a simple mapfile would appearUsing Mapfiles Defining Syntax for Mapfile Directives Attributes and their values Defining Mapfile Segment DeclarationsSegment Flags Segment declarations support the following segment flagsDefining Mapfile Section Mapping Directives Mapfile Segment Declaration ExamplesSection attributes and their valid values are as follows Placement of Segments in an Executable Internal Map StructureMapping Input Sections to Segments Map Structure Mapfile Option Error Messages Fatal ErrorsMapfile Option Error Messages Linker Optimizations Invoking Linker Optimizations from the Compile LineUnused Procedure Elimination with +Oprocelim Incompatibilities with other OptionsComplete Executables Profile-Based Optimization PA-RISC Using PBO When to Use PBOHow to Use PBO Instrumenting +I/-I Startup File icrt0.o -I Linker OptionCode Generation from I-SOMs Profiling Building Portable Code with Linker OptimizationStoring Profile Information for Multiple Programs Optimizing Based on Profile Data +P/-P -P Linker OptionSpecifying a Different flow.data with Flowdata Using The flow.data FileSpecifying a Different flow.data File with +df Interaction between Flowdata and +dfUsing PBO to Optimize Shared Libraries Selecting an Optimization Level with PBOUsing PBO with ld -r Restrictions and Limitations of PBO Size Compatibility with 9.0 PBO Essentially emptyIncremental Linking Options to Improve TLB Hit RatesProfile-Based Optimization Itanium Example 19 ExamplesAny of the padding spaces have been exhausted Shared Library Processing Using Incremental Linking OptionsArchive Library Processing PerformanceReusing Compiled Object Files PA-RISC Improving Performance with the Global Symbol TableImproving Performance by Optimizing the Hash Table Size Improving Shared Library Start-Up Time with fastbind Improving Performance with Function Symbol AliasingUsing fastbind Example 20 ExampleInvoking fastbind from the Linker How to Tell if fastbind Information is CurrentInvoking the fastbind Tool Example 21 ExampleExample 22 Example Removing fastbind Information from a FileTurning off fastbind at Run Time See the fastbind1 manGlossary SOM PBO Rpath