For the sake of people stumbling on this post a long time from now:
I solved my immediate problem by running:
echo stop <>/prog/33/dbgctl
The <> redirection opens the file for reading and writing, not just for
writing, and solves the "permission denied" issue.
However, Inferno's sh(1) man pages mentions
A file descriptor may be redirected to an already open descriptor by
writing >[fd0=fd1] or <[fd0=fd1]. Fd1 is a previously opened file de‐
scriptor and fd0 becomes a new copy (in the sense of sys-dup(2)) of it.
But I see no hint on how to actually open a file and get a file
descriptor.
It seems that there is a way to call limbo from sh, so maybe the open
system call can be called from sh, but I haven't discovered the syntax
yet.
Anyway, if anybody knows, I'll be glad to know too, in the meantime, my
current hurdle is cleared so off I go.
Cheers,
Edouard.
Edouard Klein <e...@rdklein.fr> writes:
> Thanks Ron :)
>
> In DIS assembly, this is written as jmp $0, which can be changed to jmp
> $1 when I want to disable the loop and spare myself from decreasing all
> PC offsets in the code.
>
>
> Now, I have another problem: /prog/N/dbgctl can't be written to :/
>
>
> Here is how to reproduce:
>
> Save the file below as hello.s
> asm hello.s # Assemble it
> hello& # Run it
> bind '#p' /prog # Mount /prog
> ps # Get the pid, assume e.g. 33
> echo stop > /prog/33/dbgctl
>
> This yields
> sh: cannot open /prog/33/dbgctl: permission denied
>
> instead of stopping the program.
>
> But I can still kill it with
> echo kill > /prog/33/ctl
> sh: 33 "Command":killed
>
> I have no idea what's wrong. The dbgctl has mode --rw-r--r-- so I should
> be able to write to it.
>
> devprog.c has this snippet
>
>
> case Qdbgctl:
> if(SECURE || p->group->flags&Pprivatemem || omode != ORDWR)
> error(Eperm);
>
> Which seems to indicate that the simple > redirection may fail because
> it would only by an open in write mode.
>
> Is there a way, with Inferno's sh, to open a file in RW and get a file
> descriptor (kinda like bash's exec N<> fname) ?
>
> Is the problem stemming from something else ?
>
> Any ideas, no matter how far fetched or off the cuff, would be welcome
> as I'm banging my head against the wall, and the wall is starting to
> suffer.
>
> Thanks in advance,
>
> Cheers,
>
> Edouard
>
>
>
> ------------hello.s--------------
> #0
> jmp $1
> load 0(mp),$0,12(mp) # Loads "$Sys" into @mp+12, loading the link
> descriptors at $0
> # ???: why 12 in @mp+12
> # ???: where is $0 ?
> frame $1,44(fp) # Stores in @fp+44 (44 bytes after the current
> frame pointer)
> # a pointer to a new stack frame to local-call
> to function of type $1
> # ???: Why +44 ?
> movp 4(mp),32(44(fp)) # 32 after said new frame, store a pointer to
> @mp+4, the string to print
> # ???: Why 32 ?
> lea 40(fp),16(44(fp)) # Stores the address of @fp+40 in 16 after
> said new frame
> # ???: Why 40 ? Maybe because type $2 is 40
> bytes long
> # ???: Why 16 ?
> mcall 44(fp),$0,12(mp) # Call, in module @mp+12 ($Sys), the first
> function in linkage record array $0, in frame @fp+44
> ret # Return
> entry 0, 2 # Entrypoint is at the beginning of the
> instruction stream (offset 0)
> # The function type of this entry point is
> $2 (offset 2)
> desc $0,16,"f0" # Type $0 is 16 bytes == 4 words long, all
> pointers
> desc $1,40,"0080" # Type $1 is 40 bytes == 10 words long, the
> ninth is a pointer
> desc $2,48,"00c0" # Type $2 is 48 bytes == 12 words long, the
> ninth and tenth are pointers
> var @mp,16 # Define the module pointer, of length 16
> string @mp+0,"$Sys" # The name of the module to load
> string @mp+4,"hello world and more\n" # The string to print
> module Command # The module name
> link 2,0,0x4244b354,"init" # The doc is wrong, its desc, pointer,
> ... not pointer, desc...
> # it is the list of exported symbols for the
> module.
> ldts @ldt,1 # This look like the imported symbols from $Sys
> word @ldt+0,1
> ext @ldt+4,0xac849033,"print"
> source "/tmp/quatorze/hello.b"
>
>
>
> ron minnich <rminn...@gmail.com> writes:
>
>> I put a
>> 1:jump 1
>> At the start, when I need to do this and have no other way.
>>
>> On Mon, Jul 22, 2024 at 01:28 Edouard Klein <e...@rdklein.fr> wrote:
>>
>> Hi !
>>
>> I'm writing dis assembly, and I would like to debug my program right
>> from the entrypoint.
>>
>> I intend to use the /prog filesystem for that, thanks to which one can
>> stop a program by echoing "stop" to dbgctl file.
>>
>> However, what I need to do is stop the program at the very start.
>>
>> I have multiple ideas, such as introducing a sleep or a read that would
>> let me enough time to stop the program, but they have the bad property
>> of modifying the program.
>>
>> I could create a loader program that would exec the target program and
>> stop the loader right before the exec, and I suspect (but I'm not sure)
>> that would let me stop the target program.
>>
>> But these all sound very rube goldbergy to me.
>>
>> Is there a way to start a program in a stopped state that I have
>> overlooked ?
>>
>> Thanks in advance,
>>
>> Cheers,
>>
>> Edouard.
>>
>> 9fans / 9fans / see discussions + participants + delivery options Permalink
------------------------------------------
9fans: 9fans
Permalink:
https://9fans.topicbox.com/groups/9fans/T4297f451b18d599a-M798e4b1249a2536aa222a53b
Delivery options: https://9fans.topicbox.com/groups/9fans/subscription
