On 5/4/23 09:43, Bernd Oppolzer wrote:
Am 04.04.2023 um 23:37 schrieb Charles Mills:
I just had a similar problem: "how do you determine your entry R0
from C?" I asked here and got no answer.
with native C, this is not possible IMO;
It certainly is possible using inline "__asm" blocks. Check out IBM's
zoslib which has a really load/call/delete functions that can also AMODE
switch
https://github.com/ibmruntimes/zoslib/blob/cc10b7c1d6211a2c28b10b540bf406c7148fbf4f/src/zos.cc#L1946
what I did: I wrote a (very small) ASSEMBLER routine which can be
called from everywhere and simply stores
the actual values of the registers 0 to 15 in a vector of 16 void
pointers passed by the C caller.
something like
extern void ccregs (void **regs);
void *regtable [16];
...
ccregs (regtable);
this way, you get - for example - regtable [13], which is the content
of GR 13 at the time of the ccregs call.
GR 13 points to the current save area a.k.a. stack frame. From this
save area, you can walk up to the
save area of the caller and find the registers at the time of the call
of the current function ... this can
all be done using C. It is, BTW, even possible to analyse the whole
save area chain this way,
including the names and addresses etc. of the surrounding stack
frames, and the entry point,
return addresses and so on ... a complete stack trace, if you want.
All this can be done during program run,
without interrupting or abending the current process or function.
Finding the R0 at the time of the call is very simple, once you have
the current R13.
HTH, kind regards
Bernd
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