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view content of .obj file generated by MSVC compiler ?

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  • V Vinoth Rajendran4

    @jsulm : I would like to know the value of the static variable , and where these variable will be placed in memory layout.
    I was asked this question in an interview. So I would like to know about it.

    jsulmJ Offline
    jsulmJ Offline
    jsulm
    Lifetime Qt Champion
    wrote on last edited by
    #7

    @Vinoth-Rajendran4 See https://www.geeksforgeeks.org/memory-layout-of-c-program/

    https://forum.qt.io/topic/113070/qt-code-of-conduct

    V 1 Reply Last reply
    0
    • jsulmJ jsulm

      @Vinoth-Rajendran4 See https://www.geeksforgeeks.org/memory-layout-of-c-program/

      V Offline
      V Offline
      Vinoth Rajendran4
      wrote on last edited by
      #8

      @jsulm : memory layout, i am aware.
      But like to know, if we could see the value of static variable in object file ?

      jsulmJ 1 Reply Last reply
      0
      • V Vinoth Rajendran4

        @jsulm : memory layout, i am aware.
        But like to know, if we could see the value of static variable in object file ?

        jsulmJ Offline
        jsulmJ Offline
        jsulm
        Lifetime Qt Champion
        wrote on last edited by
        #9

        @Vinoth-Rajendran4 said in view content of .obj file generated by MSVC compiler ?:

        if we could see the value of static variable in object file ?

        Of couse you can - use a hex editor.
        See "4. Let us initialize the static variable which will then be stored in the Data Segment (DS)" in the link I provided.

        https://forum.qt.io/topic/113070/qt-code-of-conduct

        1 Reply Last reply
        1
        • Kent-DorfmanK Offline
          Kent-DorfmanK Offline
          Kent-Dorfman
          wrote on last edited by
          #10
          NM(1)                                                                                                      GNU Development Tools                                                                                                     NM(1)
          
          NAME
                 nm - list symbols from object files
          
          SYNOPSIS
                 nm [-A|-o|--print-file-name] [-a|--debug-syms]
                    [-B|--format=bsd] [-C|--demangle[=style]]
                    [-D|--dynamic] [-fformat|--format=format]
                    [-g|--extern-only] [-h|--help]
                    [-l|--line-numbers] [--inlines]
                    [-n|-v|--numeric-sort]
                    [-P|--portability] [-p|--no-sort]
                    [-r|--reverse-sort] [-S|--print-size]
                    [-s|--print-armap] [-t radix|--radix=radix]
                    [-u|--undefined-only] [-V|--version]
                    [-X 32_64] [--defined-only] [--no-demangle]
                    [--plugin name]
                    [--no-recurse-limit|--recurse-limit]]
                    [--size-sort] [--special-syms]
                    [--synthetic] [--with-symbol-versions] [--target=bfdname]
                    [objfile...]
          
          DESCRIPTION
                 GNU nm lists the symbols from object files objfile....  If no object files are listed as arguments, nm assumes the file a.out.
          
                 For each symbol, nm shows:
          
                 ·   The symbol value, in the radix selected by options (see below), or hexadecimal by default.
          
                 ·   The symbol type.  At least the following types are used; others are, as well, depending on the object file format.  If lowercase, the symbol is usually local; if uppercase, the symbol is global (external).  There are
                     however a few lowercase symbols that are shown for special global symbols ("u", "v" and "w").
          
                     "A" The symbol's value is absolute, and will not be changed by further linking.
          
                     "B"
                     "b" The symbol is in the BSS data section.  This section typically contains zero-initialized or uninitialized data, although the exact behavior is system dependent.
          
                     "C" The symbol is common.  Common symbols are uninitialized data.  When linking, multiple common symbols may appear with the same name.  If the symbol is defined anywhere, the common symbols are treated as undefined
                         references.
          
                     "D"
                     "d" The symbol is in the initialized data section.
          
                     "G"
                     "g" The symbol is in an initialized data section for small objects.  Some object file formats permit more efficient access to small data objects, such as a global int variable as opposed to a large global array.
          
                     "i" For PE format files this indicates that the symbol is in a section specific to the implementation of DLLs.  For ELF format files this indicates that the symbol is an indirect function.  This is a GNU extension to the
                         standard set of ELF symbol types.  It indicates a symbol which if referenced by a relocation does not evaluate to its address, but instead must be invoked at runtime.  The runtime execution will then return the value to
                         be used in the relocation.
          
                     "I" The symbol is an indirect reference to another symbol.
          
                     "N" The symbol is a debugging symbol.
          
                     "p" The symbols is in a stack unwind section.
          
                     "R"
                     "r" The symbol is in a read only data section.
          
                     "S"
                     "s" The symbol is in an uninitialized or zero-initialized data section for small objects.
          
          
          
          JonBJ V 2 Replies Last reply
          1
          • Kent-DorfmanK Kent-Dorfman
            NM(1)                                                                                                      GNU Development Tools                                                                                                     NM(1)
            
            NAME
                   nm - list symbols from object files
            
            SYNOPSIS
                   nm [-A|-o|--print-file-name] [-a|--debug-syms]
                      [-B|--format=bsd] [-C|--demangle[=style]]
                      [-D|--dynamic] [-fformat|--format=format]
                      [-g|--extern-only] [-h|--help]
                      [-l|--line-numbers] [--inlines]
                      [-n|-v|--numeric-sort]
                      [-P|--portability] [-p|--no-sort]
                      [-r|--reverse-sort] [-S|--print-size]
                      [-s|--print-armap] [-t radix|--radix=radix]
                      [-u|--undefined-only] [-V|--version]
                      [-X 32_64] [--defined-only] [--no-demangle]
                      [--plugin name]
                      [--no-recurse-limit|--recurse-limit]]
                      [--size-sort] [--special-syms]
                      [--synthetic] [--with-symbol-versions] [--target=bfdname]
                      [objfile...]
            
            DESCRIPTION
                   GNU nm lists the symbols from object files objfile....  If no object files are listed as arguments, nm assumes the file a.out.
            
                   For each symbol, nm shows:
            
                   ·   The symbol value, in the radix selected by options (see below), or hexadecimal by default.
            
                   ·   The symbol type.  At least the following types are used; others are, as well, depending on the object file format.  If lowercase, the symbol is usually local; if uppercase, the symbol is global (external).  There are
                       however a few lowercase symbols that are shown for special global symbols ("u", "v" and "w").
            
                       "A" The symbol's value is absolute, and will not be changed by further linking.
            
                       "B"
                       "b" The symbol is in the BSS data section.  This section typically contains zero-initialized or uninitialized data, although the exact behavior is system dependent.
            
                       "C" The symbol is common.  Common symbols are uninitialized data.  When linking, multiple common symbols may appear with the same name.  If the symbol is defined anywhere, the common symbols are treated as undefined
                           references.
            
                       "D"
                       "d" The symbol is in the initialized data section.
            
                       "G"
                       "g" The symbol is in an initialized data section for small objects.  Some object file formats permit more efficient access to small data objects, such as a global int variable as opposed to a large global array.
            
                       "i" For PE format files this indicates that the symbol is in a section specific to the implementation of DLLs.  For ELF format files this indicates that the symbol is an indirect function.  This is a GNU extension to the
                           standard set of ELF symbol types.  It indicates a symbol which if referenced by a relocation does not evaluate to its address, but instead must be invoked at runtime.  The runtime execution will then return the value to
                           be used in the relocation.
            
                       "I" The symbol is an indirect reference to another symbol.
            
                       "N" The symbol is a debugging symbol.
            
                       "p" The symbols is in a stack unwind section.
            
                       "R"
                       "r" The symbol is in a read only data section.
            
                       "S"
                       "s" The symbol is in an uninitialized or zero-initialized data section for small objects.
            
            
            
            JonBJ Offline
            JonBJ Offline
            JonB
            wrote on last edited by JonB
            #11

            @Kent-Dorfman
            The OP asks about .obj files from MSVC. You sure UNIX/GNU nm is available and works on these?

            Kent-DorfmanK 1 Reply Last reply
            0
            • JonBJ JonB

              @Kent-Dorfman
              The OP asks about .obj files from MSVC. You sure UNIX/GNU nm is available and works on these?

              Kent-DorfmanK Offline
              Kent-DorfmanK Offline
              Kent-Dorfman
              wrote on last edited by
              #12

              @JonB if the object formt is COFF then it will work, even if OP has to build the utility themself. online info suggests that .obj format in windows is in fact COFF.

              JonBJ 1 Reply Last reply
              0
              • Kent-DorfmanK Kent-Dorfman

                @JonB if the object formt is COFF then it will work, even if OP has to build the utility themself. online info suggests that .obj format in windows is in fact COFF.

                JonBJ Offline
                JonBJ Offline
                JonB
                wrote on last edited by
                #13

                @Kent-Dorfman
                I see, if you say so. Still not sure that OP would have a GNU nm utility available. FWIW, What COFF (windows .obj object file) viewers are available? for example states

                I am only aware of 2:

                dumpbin which is included with Visual Studio

                PEView from http://wjradburn.com/software/

                JonBJ 1 Reply Last reply
                0
                • Kent-DorfmanK Offline
                  Kent-DorfmanK Offline
                  Kent-Dorfman
                  wrote on last edited by Kent-Dorfman
                  #14

                  @JonB said in view content of .obj file generated by MSVC compiler ?:

                  Still not sure that OP would have a GNU nm utility available.

                  mingw provides the whole slew of gnu utilities as windows native executables. nm should be available, at which point the mingw exe can be used to process the windows native object file.

                  With a caveat that most folks would probably overlook: OP wants to process C++ object files, in which case the symbol names will probably be name-mangled, unless they were declared as extern "C" {}

                  JonBJ 1 Reply Last reply
                  1
                  • Kent-DorfmanK Kent-Dorfman

                    @JonB said in view content of .obj file generated by MSVC compiler ?:

                    Still not sure that OP would have a GNU nm utility available.

                    mingw provides the whole slew of gnu utilities as windows native executables. nm should be available, at which point the mingw exe can be used to process the windows native object file.

                    With a caveat that most folks would probably overlook: OP wants to process C++ object files, in which case the symbol names will probably be name-mangled, unless they were declared as extern "C" {}

                    JonBJ Offline
                    JonBJ Offline
                    JonB
                    wrote on last edited by JonB
                    #15

                    @Kent-Dorfman said in view content of .obj file generated by MSVC compiler ?:

                    mingw provides the whole slew of gnu utilities as windows native executables. nm should be available,

                    Ooohhh, sorry, right, that makes sense!

                    Though I thought MinGW did .o not .obj files, I thought that meant MSVC. But what do I know?! :)

                    1 Reply Last reply
                    0
                    • Chris KawaC Offline
                      Chris KawaC Offline
                      Chris Kawa
                      Lifetime Qt Champion
                      wrote on last edited by
                      #16

                      You don't need any unix or otherwise external tools. MSVC installation already comes with the dumpbin utility that lets you see various information about the structure and contents of COFF files. It also undecorates C++ function names, so no problem there either.

                      V 1 Reply Last reply
                      3
                      • Chris KawaC Chris Kawa

                        You don't need any unix or otherwise external tools. MSVC installation already comes with the dumpbin utility that lets you see various information about the structure and contents of COFF files. It also undecorates C++ function names, so no problem there either.

                        V Offline
                        V Offline
                        Vinoth Rajendran4
                        wrote on last edited by
                        #17

                        @Chris-Kawa : Thanks for the utility tool suggestion.

                        1 Reply Last reply
                        0
                        • Kent-DorfmanK Kent-Dorfman
                          NM(1)                                                                                                      GNU Development Tools                                                                                                     NM(1)
                          
                          NAME
                                 nm - list symbols from object files
                          
                          SYNOPSIS
                                 nm [-A|-o|--print-file-name] [-a|--debug-syms]
                                    [-B|--format=bsd] [-C|--demangle[=style]]
                                    [-D|--dynamic] [-fformat|--format=format]
                                    [-g|--extern-only] [-h|--help]
                                    [-l|--line-numbers] [--inlines]
                                    [-n|-v|--numeric-sort]
                                    [-P|--portability] [-p|--no-sort]
                                    [-r|--reverse-sort] [-S|--print-size]
                                    [-s|--print-armap] [-t radix|--radix=radix]
                                    [-u|--undefined-only] [-V|--version]
                                    [-X 32_64] [--defined-only] [--no-demangle]
                                    [--plugin name]
                                    [--no-recurse-limit|--recurse-limit]]
                                    [--size-sort] [--special-syms]
                                    [--synthetic] [--with-symbol-versions] [--target=bfdname]
                                    [objfile...]
                          
                          DESCRIPTION
                                 GNU nm lists the symbols from object files objfile....  If no object files are listed as arguments, nm assumes the file a.out.
                          
                                 For each symbol, nm shows:
                          
                                 ·   The symbol value, in the radix selected by options (see below), or hexadecimal by default.
                          
                                 ·   The symbol type.  At least the following types are used; others are, as well, depending on the object file format.  If lowercase, the symbol is usually local; if uppercase, the symbol is global (external).  There are
                                     however a few lowercase symbols that are shown for special global symbols ("u", "v" and "w").
                          
                                     "A" The symbol's value is absolute, and will not be changed by further linking.
                          
                                     "B"
                                     "b" The symbol is in the BSS data section.  This section typically contains zero-initialized or uninitialized data, although the exact behavior is system dependent.
                          
                                     "C" The symbol is common.  Common symbols are uninitialized data.  When linking, multiple common symbols may appear with the same name.  If the symbol is defined anywhere, the common symbols are treated as undefined
                                         references.
                          
                                     "D"
                                     "d" The symbol is in the initialized data section.
                          
                                     "G"
                                     "g" The symbol is in an initialized data section for small objects.  Some object file formats permit more efficient access to small data objects, such as a global int variable as opposed to a large global array.
                          
                                     "i" For PE format files this indicates that the symbol is in a section specific to the implementation of DLLs.  For ELF format files this indicates that the symbol is an indirect function.  This is a GNU extension to the
                                         standard set of ELF symbol types.  It indicates a symbol which if referenced by a relocation does not evaluate to its address, but instead must be invoked at runtime.  The runtime execution will then return the value to
                                         be used in the relocation.
                          
                                     "I" The symbol is an indirect reference to another symbol.
                          
                                     "N" The symbol is a debugging symbol.
                          
                                     "p" The symbols is in a stack unwind section.
                          
                                     "R"
                                     "r" The symbol is in a read only data section.
                          
                                     "S"
                                     "s" The symbol is in an uninitialized or zero-initialized data section for small objects.
                          
                          
                          
                          V Offline
                          V Offline
                          Vinoth Rajendran4
                          wrote on last edited by
                          #18

                          @Kent-Dorfman : Thanks for suggesting nm utility.

                          1 Reply Last reply
                          0
                          • JonBJ JonB

                            @Kent-Dorfman
                            I see, if you say so. Still not sure that OP would have a GNU nm utility available. FWIW, What COFF (windows .obj object file) viewers are available? for example states

                            I am only aware of 2:

                            dumpbin which is included with Visual Studio

                            PEView from http://wjradburn.com/software/

                            JonBJ Offline
                            JonBJ Offline
                            JonB
                            wrote on last edited by JonB
                            #19

                            @JonB said in view content of .obj file generated by MSVC compiler ?:

                            (https://stackoverflow.com/questions/2262959/what-coff-windows-obj-object-file-viewers-are-available) for example states
                            I am only aware of 2:

                            dumpbin which is included with Visual Studio

                            PEView from http://wjradburn.com/software/

                            1 Reply Last reply
                            1

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