https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53927
--- Comment #17 from Pierre-Marie de Rodat <derodat at adacore dot com> ---
(In reply to Tom Tromey from comment #16)
> I'm curious if you tried it on the test case in this PR.
I did not, but it looks like it now works as expected. Here are the frame base
info for "nestee" and the static link info for "nested":
[nestee]
<69> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa)
[nested]
<aa> DW_AT_static_link : 6 byte block: 91 60 6 23 20 6 (DW_OP_fbreg:
-32; DW_OP_deref; DW_OP_plus_uconst: 32; DW_OP_deref)
... and the CFA for the two locations we will be interrested in later:
LOC CFA
0000000000400496 rsp+8
0000000000400497 rsp+16
000000000040049a rbp+16 # A
00000000004004af rsp+8
LOC CFA
000000000040053b rsp+8
000000000040053c rsp+16
000000000040053f rbp+16 # B
0000000000400564 rsp+8
Now in GDB:
$ gdb -n -q -ex 'b pr53927.c:7' -ex r --args ./pr53927
[...]
Breakpoint 1, nested (nested_arg=10) at pr53927.c:7
7 return nested_arg + 23 + self_call; /* Break here */
(gdb) bt
#0 nested (nested_arg=10) at pr53927.c:7
#1 0x000000000040052b in nestee (computer=0x7fffffffdf24, arg=10) at
pr53927.c:13
#2 0x000000000040051d in nestee (computer=0x40052d <misc>, arg=5) at
pr53927.c:11
#3 0x000000000040055e in main (argc=1, argv=0x7fffffffe058) at
pr53927.c:23
(gdb) p $pc
$1 = (void (*)()) 0x4004a4 <nested+14>
# This PC corresponds to the "B" line above: CFA = $rbp + 16
(gdb) x/1gx $rbp + 16 - 32
0x7fffffffdea0: 0x00007fffffffdf20
(gdb) x/1gx 0x00007fffffffdf20 + 32
0x7fffffffdf40: 0x00007fffffffdf60
... so the static link expression gives us the following frame base address:
0x00007fffffffdf60
(gdb) f 2
#2 0x000000000040051d in nestee (computer=0x40052d <misc>, arg=5) at
pr53927.c:11
11 arg = nestee (nested, arg + 5, 0);
# This PC corresponds to the "A" line above: CFA = $rbp + 16
(gdb) p/x $rbp + 16
$2 = 0x7fffffffdf60
So the static link expression correctly yields the frame 2's CFA.
> Yeah, growing these is to be avoided.
> My patch for this added a method to symbol_computed_ops instead.
>
> Unfortunately gitorious is acting weird so you can't see the patch
> online :-(. But you can fetch from
> https://gitorious.org/binutils-gdb/gdb.git
> and look at the branch static-link-fix if you like.
Interesting! Having a look at this: thank you! I guess you waited for the GCC
issue to be solved before submitting them to GDB?
