Aw: how to open elf file image from inside genode? libbacktrace question

[Uwe]

> Gesendet: Sonntag, 04. April 2021 um 15:18 Uhr
> Von: "Alexander Tormasov via users" <users at lists.genode.org>
> An: "Genode users mailing list" <users at lists.genode.org>
> Cc: "Alexander Tormasov" <a.tormasov at innopolis.ru>
> Betreff: how to open elf file image from inside genode? libbacktrace question
>
> During port of libbacktrace code from gcc compiler I found that I need to be able to read a.out or similar file in runtime. This library try to read original executable file and parse it for functions addresses/etc, as a part of garbage collection for golang (it parse call stack in some specific way using gcc-specific calls).
>
> I have to port to genode the following code from src/lib/gcc/libbacktrace/fileline.c:
>
>   for (pass = 0; pass < 5; ++pass)
>     {
>       int does_not_exist;
>
>       switch (pass)
>   {
>   case 0:
>     filename = state->filename;
>     break;
>   case 1:
>     filename = getexecname ();
>     break;
>   case 2:
>     filename = "/proc/self/exe";
>     break;
>   case 3:
>     filename = "/proc/curproc/file";
>     break;
>   case 4:
>     snprintf (buf, sizeof (buf), "/proc/%ld/object/a.out",
>         (long) getpid ());
>     filename = buf;
>     break;
>   default:
>     abort ();
>   }
>
> best idea is to implement library call getexecname(), e.g. as a part of libc.
>
Your parent needs a ROMFile capability to run
your program. Ask it for that capability to read
your own file. You can call that RPC  getexecname
or whatever strikes your fancy.
Of course you would have to extend the official
interface to the parent else your program could
be started from a component that doesn't
implement that function.
Or you can write a wrapper that guarantees to
implement that function and start your program
exclusively with that wrapper. You can call your
wrapper "go run" or whatever strikes your fancy.
> Anyway, this is complex question, because we need to be able to open it and read a content later. How to configure this in run file?
>
> PS for better understanding why I need this - call stack where it is called, from gdb:
>
> #0 fileline_initialize (state=0x29000, error_callback=0x1198543 <error_callback>, data=0x405fe770) at /var/services/homes/admin/gen/21.02/contrib/libbacktrace-cabcd83bc903137f607eda3a65eb09feaa5f507e/src/lib/gcc/libbacktrace/fileline.c:102
> #1  0x000000000119a9a5 in backtrace_pcinfo (state=0x29000, pc=0x1198610, callback=0x119808e <callback>, error_callback=0x1198543 <error_callback>, data=0x405fe770) at /var/services/homes/admin/gen/21.02/contrib/libbacktrace-cabcd83bc903137f607eda3a65eb09feaa5f507e/src/lib/gcc/libbacktrace/fileline.c:177
> #2  0x000000000119accc in unwind (context=0x405fe420, vdata=0x405fe700) at /var/services/homes/admin/gen/21.02/contrib/libbacktrace-cabcd83bc903137f607eda3a65eb09feaa5f507e/src/lib/gcc/libbacktrace/backtrace.c:91
> #3  0x00000000011a87e9 in _Unwind_Backtrace (trace=0x119abfc <unwind>, trace_argument=0x405fe700) at /genodelabs-genode-2491eee/contrib/gcc-3cade18cf9defeefa714aa91de3b157fbad4aa18/src/noux-pkg/gcc/libgcc/unwind.inc:307
> #4  0x000000000119ada2 in backtrace_full (state=0x29000, skip=0x0, callback=0x119808e <callback>, error_callback=0x1198543 <error_callback>, data=0x405fe770) at /var/services/homes/admin/gen/21.02/contrib/libbacktrace-cabcd83bc903137f607eda3a65eb09feaa5f507e/src/lib/gcc/libbacktrace/backtrace.c:127
> #5  0x0000000001198611 in runtime_callers (skip=0x2, locbuf=0xc42000e8d8, m=0x20, keep_thunks=0x0) at /var/services/homes/admin/gen/21.02/contrib/libgo-281260d9bdc27fefb62c00310025c54e1e629a2e/src/lib/gcc/libgo/runtime/go-callers.c:207
> #6  0x00000000010fdf28 in runtime.callers (skip=0x1, locbuf=...) at /var/services/homes/admin/gen/21.02/contrib/libgo-281260d9bdc27fefb62c00310025c54e1e629a2e/src/lib/gcc/libgo/go/runtime/traceback_gccgo.go:56
> #7  0x00000000010d8f7d in runtime.mcommoninit (mp=0xc42000e800) at /var/services/homes/admin/gen/21.02/contrib/libgo-281260d9bdc27fefb62c00310025c54e1e629a2e/src/lib/gcc/libgo/go/runtime/proc.go:546
> #8  0x00000000010db6c5 in runtime.allocm (_p_=0xc420008000, fn=0x121e298 <runtime.mspinning..f>, allocatestack=0x0) at /var/services/homes/admin/gen/21.02/contrib/libgo-281260d9bdc27fefb62c00310025c54e1e629a2e/src/lib/gcc/libgo/go/runtime/proc.go:1466
> #9  0x00000000010dbdb2 in runtime.newm (fn=0x121e298 <runtime.mspinning..f>, _p_=0xc420008000) at /var/services/homes/admin/gen/21.02/contrib/libgo-281260d9bdc27fefb62c00310025c54e1e629a2e/src/lib/gcc/libgo/go/runtime/proc.go:1769
> #10 0x00000000010dc360 in runtime.startm (_p_=0xc420008000, spinning=0x1) at /var/services/homes/admin/gen/21.02/contrib/libgo-281260d9bdc27fefb62c00310025c54e1e629a2e/src/lib/gcc/libgo/go/runtime/proc.go:1925
> #11 0x00000000010dc702 in runtime.wakep () at /var/services/homes/admin/gen/21.02/contrib/libgo-281260d9bdc27fefb62c00310025c54e1e629a2e/src/lib/gcc/libgo/go/runtime/proc.go:2006
> #12 0x00000000010dfabf in __go_go (fn=0x10d72f2, arg=0x0) at /var/services/homes/admin/gen/21.02/contrib/libgo-281260d9bdc27fefb62c00310025c54e1e629a2e/src/lib/gcc/libgo/go/runtime/proc.go:3144
>
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