| This document explains a couple of things that are specific to VMS. |
| There are currently two "chapters", the first deals with cross-assembly |
| issues, and the second deals with the VMS debugger and GNU-CC. |
| |
| |
| *********************************************************************** |
| ****************** Notes for Cross Assembly with VMS ****************** |
| *********************************************************************** |
| |
| If you wish to build gas on a non-VMS system to cross-assemble, |
| you should use: |
| |
| configure ${hosttype} -target=vms |
| |
| and then follow the usual procedure. The object files generated on |
| Unix will be correct from a binary point of view, but the real trick is |
| getting them to the VMS machine. The format of the object file is |
| a variable-length record, but each record contains binary data. gas |
| writes the records in the same format that VMS would expect, |
| namely a two-byte count followed by that number of bytes. |
| |
| If you try to copy the file to a VMS system using ftp, the ftp |
| protocol will screw up the file by looking for nulls (record terminator for |
| unix) and it will insert it's own record terminators at that point. This |
| will obviously corrupt the file. |
| |
| If you try to transfer the file with ftp in binary mode, the |
| file itself will not be corrupt, but VMS will think that the file contains |
| fixed-length records of 512 bytes. You can use the public-domain FILE |
| utility to change this with a command like: |
| |
| $FILE foo.o/type=variable |
| |
| If you do not have this utility available, the following program can be |
| used to perform this task: |
| |
| #include <fab.h> |
| |
| #define RME$C_SETRFM 1 |
| |
| struct FAB * fab; |
| |
| main(int argc, char * argv[]){ |
| int i, status; |
| fab = (struct FAB*) malloc(sizeof(struct FAB)); |
| *fab = cc$rms_fab; /* initialize FAB*/ |
| fab->fab$b_fac = FAB$M_PUT; |
| fab->fab$l_fop |= FAB$M_ESC; |
| fab->fab$l_ctx = RME$C_SETRFM; |
| fab->fab$w_ifi = 0; |
| for(i=1;i<argc;i++){ |
| printf("Setting %s to variable length records.\n",argv[i]); |
| fab->fab$l_fna = argv[i]; |
| fab->fab$b_fns = strlen(argv[i]); |
| status = sys$open(fab,0,0); |
| if((status & 7) != 1) lib$signal(status); |
| fab->fab$b_rfm = FAB$C_VAR; |
| status = sys$modify(fab,0,0); |
| if((status & 7) != 1) lib$signal(status); |
| status = sys$close(fab,0,0); |
| if((status & 7) != 1) lib$signal(status); |
| }; |
| } |
| |
| If you have NFS running on the VMS system, what you need to do |
| depends upon which NFS software you are running on the VMS system. There |
| are a number of different TCP/IP packages for VMS available, and only very |
| limited testing has been performed. In the tests that has been done so |
| far, the contents of the file will always be correct when transferring the |
| file via NFS, but the record attributes may or may not be correct. |
| |
| One proprietary TCP/IP/NFS package for VMS is known to |
| automatically fix the record attributes of the object file if you NFS mount |
| a unix disk from the VMS system, and if the file has a ".obj" extension on |
| the unix system. Other TCP/IP packages might do this for you as well, but |
| they have not been checked. |
| |
| No matter what method you use to get the file to the VMS system, it is |
| always a good idea to check to make sure that it is the correct type by |
| doing a "$dir/full" on the object file. The desired record attributes will |
| be "None". Undesirable record attributes will be "Stream-LF" or anything |
| else. |
| |
| Once you get the files on the VMS system, you can check their integrity |
| with the "$anal/obj" command. (Naturally at some point you should rename |
| the .o files to .obj). As far as the debugger is concerned, the records |
| will be correct, but the debugger will not be able to find the source files, |
| since it only has the file name, and not the full directory specification. |
| You must give the debugger some help by telling it which directories to |
| search for the individual files - once you have done this you should be |
| able to proceed normally. |
| |
| It is a good idea to use names for your files which will be valid |
| under VMS, since otherwise you will have no way of getting the debugger to |
| find the source file when deugging. |
| |
| The reason for this is that the object file normally contins specific |
| information that the debugger can use to positively identify a file, and if |
| you are assembling on a unix system this information simply does not exist |
| in a meaningful way. You must help the debugger by using the "SET FILE=" |
| command to tell the debugger where to look for source files. The debugger |
| records will be correct, except that the debugger will not be initially |
| able to find the source files. You can use the "SET FILE" command to tell |
| the debugger where to look for the source files. |
| |
| I have only tested this with a SVr4 i486 machine, and everything seems to |
| work OK, with the limited testing that I have done. Other machines may |
| or may not work. You should read the chapters on cross-compilers in the gcc |
| manual before fooling with this. Since gas does not need to do any floating |
| point arithmetic, the floating point constants that are generated here should |
| be correct - the only concern is with constant folding in the main compiler. |
| The range and precision of floats and doubles are similar on the 486 (with |
| a builtin 80387) and the VAX, although there is a factor of 2 to 4 |
| difference in the range. The double, as implemented on the 486, is quite |
| similar to the G_FLOAT on the VAX. |
| |
| *********************************************************************** |
| ****************** Notes for using GNU CC with the VMS debugger******** |
| *********************************************************************** |
| |
| |
| 1) You should be aware that GNU-C, as with any other decent compiler, |
| will do things when optimization is turned on that you may not expect. |
| Sometimes intermediate results are not written to variables, if they are only |
| used in one place, and sometimes variables that are not used at all will not be |
| written to the symbol table. Also, parameters to inline functions are often |
| inaccessible. You can see the assembly code equivalent by using KP7 in the |
| debugger, and from this you can tell if in fact a variable should have the |
| value that you expect. You can find out if a variable lives withing a register |
| by doing a 'show symbol/addr'. |
| |
| 2) Overly complex data types, such as: |
| |
| int (*(*(*(*(*(* sarr6)[1])[1])[2])[3])[4])[5]; |
| |
| will not be debugged properly, since the debugging record overflows an internal |
| debugger buffer. gcc-as will convert these to *void as far as the debugger |
| symbol table is concerned, which will avoid any problems, and the assembler |
| will give you a message informing you that this has happened. |
| |
| 3) You must, of course, compile and link with /debug. If you link |
| without debug, you still get traceback table in the executable, but there is no |
| symbol table for variables. |
| |
| 4) Included in the patches to VMS.C are fixes to two bugs that are |
| unrelated to the changes that I have made. One of these made it impossible to |
| debug small programs sometimes, and the other caused the debugger to become |
| confused about which routine it was in, and give this incorrect info in |
| tracebacks. |
| |
| 5) If you are using the GNU-C++ compiler, you should modify the |
| compiler driver file GNU_CC:[000000]GCC.COM (or GXX.COM). If you have a |
| separate GXX.COM, then you need to change one line in GXX.COM to: |
| $ if f$locate("D",p2) .ne. P2_Length then Debug = " ""-G0""" |
| Notice zero---> ^ |
| If you are using a GCC.COM that does both C and C++, add the following lines to |
| GCC.COM: |
| |
| $! |
| $! Use old style debugging records for VMS |
| $! |
| $ if (Debug.nes."" ).and. Plus then Debug = " ""-G0""" |
| |
| after the variables Plus and Debug are set. The reason for this, is that C++ |
| compiler by default generates debugging records that are more complex, |
| with many new syntactical elements that allow for the new features of the |
| language. The -G0 switch tells the C++ compiler to use the old style debugging |
| records. Until the debugger understands C++ there is not any point to try and |
| use the expanded syntax. |
| |
| 6) When you have nested scopes, i.e.: |
| main(){ |
| int i; |
| {int i; |
| {int i; |
| };};} |
| and you say "EXAM i" the debugger needs to figure out which variable you |
| actually want to reference. I have arranged things to define a block to the |
| debugger when you use brackets to enter a new scope, so in the example above, |
| the variables would be described as: |
| TEST\main\i |
| TEST\main\$0\i |
| TEST\main\$0\$0\i |
| At each level, the block name is a number with a dollar sign prefix, the |
| numbers start with 0 and count upward. When you say EXAM i, the debugger looks |
| at the current PC, and decides which block it is currently in. It works from |
| the innermost level outward until it finds a block that has the variable "i" |
| defined. You can always specify the scope explicitly. |
| |
| 7) With C++, there can be a lot of inline functions, and it would be |
| rather restrictive to force the user to debug the program by converting all of |
| the inline functions to normal functions. What I have done is to essentially |
| "add" (with the debugger) source lines from the include files that contain the |
| inline functions. Thus when you step into an inline function it appears as if |
| you have called the function, and you can examine variables and so forth. |
| There are several *very* important differences, however. First of all, since |
| there is no function call involved, you cannot step over the inline function |
| call - you always step into it. Secondly, since the same source lines are used |
| in many locations, there is a separate copy of the source for *each* usage. |
| Without this, breakpoints do not work, since we must have a 1-to-1 mapping |
| between source lines and PC. |
| Since you cannot step over inline function calls, it can be a real pain |
| if you are not really interested in what is going on for that function call. |
| What I have done is to use the "-D" switch for the assembler to toggle the |
| following behavior. With the "-D" switch, all inline functions are included in |
| the object file, and you can debug everything. Without the "-D" switch |
| (default case with VMS implementation), inline functions are included *only* if |
| they did not come from system header files (i.e. from GNU_CC_INCLUDE: or |
| GNU_GXX_INCLUDE:). Thus, without the switch the user only debugs his/her own |
| inline functions, and not the system ones. (This is especially useful if you do |
| a lot of stream I/O in C++). This probably will not provide enough granularity |
| for many users, but for now this is still somewhat experimental, and I would |
| like to reflect upon it and get some feedback before I go any further. |
| Possible solutions include an interactive prompting, a logical name, or a new |
| command line option in gcc.c (which is then passed through somehow to the guts |
| of the assembler). |
| The inline functions from header files appear after the source code |
| for the source file. This has the advantage that the source file itself is |
| numbered with the same line numbers that you get with an editor. In addition, |
| the entire header file is not included, since the assembler makes a list of |
| the min and max source lines that are used, and only includes those lines from |
| the first to the last actually used. (It is easy to change it to include the |
| whole file). |
| |
| 8) When you are debugging C++ objects, the object "this" is refered to |
| as "$this". Actually, the compiler writes it as ".this", but the period is |
| not good for the debugger, so I have a routine to convert it to a $. (It |
| actually converts all periods to $, but only for variables, since this was |
| intended to allow us to access "this". |
| |
| 9) If you use the asm("...") keyword for global symbols, you will not |
| be able to see that symbol with the debugger. The reason is that there are two |
| records for the symbol stored in the data structures of the assembler. One |
| contains the info such as psect number and offset, and the other one contains |
| the information having to do with the data type of the variable. In order to |
| debug as symbol, you need to be able to coorelate these records, and the only |
| way to do this is by name. The record with the storage attributes will take |
| the name used in the asm directive, and the record that specifies the data type |
| has the actual variable name, and thus when you use the asm directive to change |
| a variable name, the symbol becomes invisible. |
| |
| 10) Older versions of the compiler ( GNU-C 1.37.92 and earlier) place |
| global constants in the text psect. This is unfortunate, since to the linker |
| this appears to be an entry point. I sent a patch to the compiler to RMS, |
| which will generate a .const section for these variables, and patched the |
| assembler to put these variables into a psect just like that for normal |
| variables, except that they are marked NOWRT. static constants are still |
| placed in the text psect, since there is no need for any external access. |