[TUHS] 2.11BSD cross compiling update

Steve Simon steve at quintile.net
Sat Jan 14 05:02:25 AEST 2017


working with aged compilers is different. the biggest problem i had was the shared namespace for all structure members.

i had great success with hash8 many years ago. i am fairly sure that this still available in comp.sources.unix or comp.sources.misc.

-Steve


> On 13 Jan 2017, at 17:57, Nick Downing <downing.nick at gmail.com> wrote:
> 
> So I got a fair bit further advanced on my 2.11BSD cross compiler
> project, at the moment it can make a respectable unix tree (/bin /usr
> etc) with a unix kernel and most software in it. I unpacked the
> resulting tarball and chrooted into it on a running SIMH system and it
> worked OK, was a bit rough around the edges (missing a few necessary
> files in /usr/share and that kind of thing) but did not crash. I
> haven't tested the kernel recently but last time I tested it, it
> booted, and the checksys output is OK.
> 
> I then ended up doing a fair bit of re-engineering, how this came
> about was that I had to port the timezone compiler (zic) to run on the
> Linux cross compilation host, since the goal is eventually to build a
> SIMH-bootable disk (filesystem) with everything on it. This was a bit
> involved, it crashed initially and it turned out it was doing
> localtime() on really small and large values to try to figure out the
> range of years the system could handle. On the Linux system this
> returns NULL for unreasonable time_t values which POSIX allows it to
> do. Hence the crash. It wasn't too obvious how to port this code. (But
> whatever I did, it had to produce the exact same timezone files as a
> native build).
> 
> So what I ended up doing was to port a tiny subset of 2.11BSD libc to
> Linux, including its types. I copied the ctime.c module and prefixed
> everything with "cross_" so there was "cross_time_t" and so forth, and
> "#include <time.h>" became "#include <cross/time.h>", in turn this
> depends on "#include <cross/sys/types.h>" and so on. That way, the
> original logic worked unchanged.
> 
> I decided to also redo the cross compilation tools (as, cc, ld, nm,
> ranlib and so on) using the same approach, since it was conceptually
> elegant. This involved making e.g. "cross_off_t" and "struct
> cross_exec" available by "#include <cross/a.out.h>", and obviously the
> scheme extends to whatever libc functions we want to use. In
> particular we use floating point, and I plan to make a "cross_atof()"
> for the C compiler's PDP-11-formatted floating-point constant
> handling, etc. (This side of things, like the cross tools, was
> working, but was not terribly elegant before).
> 
> So then I got to thinking, actually this is an incredibly powerful
> approach. Instead of just going at it piecemeal, would it not be
> easier just to port the entire thing across? To give an example what I
> mean, the linker contains code like this:
>  if (nund==0)
>    printf("Undefined:\n");
>  nund++;
>  printf("%.*s\n", NNAMESIZE, sp->n_name);
> It is printing n_name from a fixed-size char array, so to save the
> cost of doing a strncpy they have used that "%.*s" syntax which tells
> printf not to go past the end of the char array. But this isn't
> supported in Linux. I keep noticing little problems like this
> (actually I switched off "-Wformat" which was possibly a bad idea). So
> with my latest plan this will actually run the 2.11BSD printf()
> instead of the Linux printf(), and the 2.11BSD stdio (fixing various
> other breakage that occured because BUFSIZ isn't 512 on the Linux
> system), and so on. What I will do is, provide a low level syscalls
> module like cross_open(), cross_read(), cross_write() and so on, which
> just redirect the request into the normal Linux system calls, while
> adjusting for the fact that size_t is 16 bits and so forth. This will
> be really great.
> 
> In case it sounds like this is over-engineering, well bear in mind
> that one knotty problem I hadn't yet tackled is the standalone
> utilities, for instance the 2.11BSD tape distribution contains a
> standalone "restor" program which is essentially a subset of the
> kernel, including its device drivers, packaged with the normal
> "restor" utility into one executable that can be loaded off the tape.
> It was quite important to me that I get this ported over to Linux, so
> that I can produce filesystems, etc, at the Linux level, all ready to
> boot when I attach them to SIMH. But it was going to be hugely
> challenging, since compiling any program that includes more than the
> most basic kernel headers would have caused loads of conflicts with
> Linux's kernel headers and system calls. So the new approach
> completely fixes all that.
> 
> I did some experiments the last few days with a program that I created
> called "xify". What it does is to read a C file, and to every
> identifier it finds, including macro names, C-level identifiers,
> include file names, etc, it prepends the sequence "x_". The logic is a
> bit convoluted since it has to leave keywords alone and it has to
> translate types so that "unsigned int" becomes "x_unsigned_int" which
> I can define with a typedef, and so on. Ancient C constructs like
> "register i;" were rather problematic, but I have got a satisfactory
> prototype system now.
> 
> I also decided to focus on 4.3BSD rather than 2.11BSD, since by this
> stage I know the internals and the build system extremely intimately,
> and I'm aware of quite a lot of inconsistencies which will be a lot of
> work to tidy up, basically things that had been hurriedly ported from
> 4.3BSD while trying not to change the corresponding 2.8~2.10BSD code
> too much. Also in the build system there are quite a few different
> ways of implementing "make depend" for example, and this annoys me, I
> did have some ambitious projects to tidy it all up but it's too
> difficult. So a fresh start is good, and I am satisfied with the
> 2.11BSD project up to this moment.
> 
> So what will happen next is basically once I have "-lx_c" (the "cross"
> version of the 4.3BSD C library) including the "xified" versions of
> the kernel headers, then I will try to get the 4.3BSD kernel running
> on top of Linux, it will be a bit like User-Mode Linux. It will use
> simulated network devices like libpcap, or basically just whatever
> SIMH uses, since I can easily drop in the relevant SIMH code and then
> connect it up using the 4.3BSD kernel's devtab. The standalone
> utilities like "restor" should then "just work". The cross toolchain
> should also "just work" apart from the floating point issue, since it
> was previously targeting the VAX which is little-endian, and the
> wordsize issues and the library issues are taken care of by "xifying".
> Very nice.
> 
> The "xifying" stuff is in a new repository 43bsd.git at my bitbucket
> (user nick_d2).
> 
> cheers, Nick



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