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diff --git a/gas/README-vms b/gas/README-vms new file mode 100644 index 0000000..796c603 --- /dev/null +++ b/gas/README-vms @@ -0,0 +1,248 @@ + 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 +seperate 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 seperate 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. |