[Bug python/27000] gdb.block_for_pc should accept a gdb.Value argument

["jwakely.gcc at gmail dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=27000

--- Comment #1 from Jonathan Wakely <jwakely.gcc at gmail dot com> ---
(In reply to Jonathan Wakely from comment #0)
> - Calling int with gdb.Value should not raise an exception if long(v) would
> work instead, just do that.
> 
> - gdb.block_for_pc should not raise exceptions for invalid values, or the
> docs should be fixed.

Actually it looks like these two are already done for GDB 10.1, I must have
tested with the wrong version, sorry.

But it would still be easier if I could use a gdb.Value directly.

Testcase:

int function ()
{
  int (*p)() = &function;
  return 0;
}
int main()
{
  return function(1);
}

On ppc64 running CentOS 7, with the system Python (2.7) and GDB 10.1 I get:

(gdb) start
Starting program: /home/jwakely/tmp/a.out 

Temporary breakpoint 2, main () at b.c:8
8         return function(1);
(gdb) step
function () at b.c:3
3         int (*p)() = &function;
(gdb) n
4         return 0;
(gdb) py p = gdb.parse_and_eval('p')
(gdb) py print p
@0x1001feb8: 0x10000550 <function>
(gdb) py b = gdb.block_for_pc(p)
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/jwakely/gcc/gdb-10.1/share/gdb/python/gdb/__init__.py", line 207,
in block_for_pc
    return current_progspace().block_for_pc(pc)
TypeError: must be integer<K>, not gdb.Value
Error while executing Python code.
(gdb) py b = gdb.block_for_pc(int(p))
(gdb) py print(b)
None
(gdb) py b2 = gdb.block_for_pc(int(p.dereference().address))
(gdb) py print(b2)
<gdb.Block object at 0x3fff9d797db0>
(gdb) py print(b2.function.name)
function


Using the CentOS 7 system GDB 7.6 it was worse:

(gdb) start
Temporary breakpoint 1 at 0x1000059c: file b.c, line 8.
Starting program: /home/jwakely/tmp/a.out 

Temporary breakpoint 1, main () at b.c:8
8         return function(1);
Missing separate debuginfos, use: debuginfo-install glibc-2.17-307.el7.1.ppc64
(gdb) step
function () at b.c:3
3         int (*p)() = &function;
(gdb) n
4         return 0;
(gdb) py p = gdb.parse_and_eval('p')
(gdb) py print(p)
@0x1001feb8: 0x10000550 <function>
(gdb) py int(p)
Traceback (most recent call last):
  File "<string>", line 1, in <module>
gdb.error: Cannot convert value to int.
Error while executing Python code.
(gdb) py b = gdb.block_for_pc(p)
Traceback (most recent call last):
  File "<string>", line 1, in <module>
TypeError: must be integer<K>, not gdb.Value
Error while executing Python code.
(gdb) py b = gdb.block_for_pc(long(p))
Traceback (most recent call last):
  File "<string>", line 1, in <module>
RuntimeError: Cannot locate object file for block.
Error while executing Python code.
(gdb) py b = gdb.block_for_pc(long(p.dereference().address)) ; print
b.function.name
function


The reason block_for_pc(long(p)) fails is that long(p) doesn't give the actual
address of the function:

(gdb) py print p
@0x1001feb8: 0x10000550 <function>
(gdb) py print "0x%x" % long(p.dereference().address)
0x10000550
(gdb) py print "0x%x" % long(p)
0x1001feb8

Presumably if a gdb.Value was passed to gdb.block_for_pc it could do that
automatically.

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