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author | Joel Brobecker <brobecker@adacore.com> | 2014-11-21 04:59:35 +0100 |
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committer | Joel Brobecker <brobecker@adacore.com> | 2014-12-13 08:26:31 -0500 |
commit | 14aba1ac0d583ebd77b7645f88308d75c0a69d0f (patch) | |
tree | 817c8621f3b34573840980efab7ea8002e71e815 | |
parent | ae6a105d22fb603dbfb956bbcedf9ae469323d55 (diff) | |
download | gdb-14aba1ac0d583ebd77b7645f88308d75c0a69d0f.zip gdb-14aba1ac0d583ebd77b7645f88308d75c0a69d0f.tar.gz gdb-14aba1ac0d583ebd77b7645f88308d75c0a69d0f.tar.bz2 |
Lift DWARF unwinder restriction in dwarf2-frame.c::dwarf2_frame_cfa
GDB is currently broken on all SPARC targets when using GCC 4.9.
When trying to print any local variable:
(gdb) p x
can't compute CFA for this frame
This is related to the fact that the compiler now generates DWARF 4
debugging info by default, and in particular that it now emits
DW_OP_call_frame_cfa, which triggers a limitation in dwarf2_frame_cfa:
/* This restriction could be lifted if other unwinders are known to
compute the frame base in a way compatible with the DWARF
unwinder. */
if (!frame_unwinder_is (this_frame, &dwarf2_frame_unwind)
&& !frame_unwinder_is (this_frame, &dwarf2_tailcall_frame_unwind))
error (_("can't compute CFA for this frame"));
We couldn't append the dwarf2 unwinder to all SPARC targets because
it does not work properly with StackGhost:
https://www.sourceware.org/ml/gdb-patches/2014-07/msg00012.html
We also later discovered that using the DWARF2 unwinder means
using it for computing the function's return address, which
is buggy when it comes to functions returning a struct (where
the return address is saved-pc+12 instead of saved-pc+8).
This is because GCC is emitting the info about the return address
as %o7/%i7 instead of the actual return address. For functions
that have debugging info, we compensate by looking at the function's
return type and add the extra +4, but for function without debug
info, we're stuck.
EricB and I twisted the issue in all the directions we could think of,
and unfortunately couldn't find a way to make it work without
introduction one regression or another.
But, stepping back a little, just removing the restriction seems to work
well for us on all both sparc-elf and {sparc,sparc64}-solaris.
After reviewing the previous discussions about this test, I could
not figure out whether some unwinders were already known to have
incompatible CFAs or if the concern was purely theoretical:
https://www.sourceware.org/ml/gdb-patches/2009-06/msg00191.html
https://www.sourceware.org/ml/gdb-patches/2009-07/msg00570.html
https://www.sourceware.org/ml/gdb-patches/2009-09/msg00027.html
At the moment, we took the approach of trying it out, and see what
happens...
gdb/ChangeLog:
PR backtrace/16215:
* dwarf2-frame.c (dwarf2_frame_cfa): Remove the restriction
the frame unwinder must either be the dwarf2_frame_unwind
or the dwarf2_tailcall_frame_unwind. Verify that this_frame's
stack_addr is valid before calling get_frame_base. Throw
an error if not valid.
Tested on sparc-solaris and sparc-elf with AdaCore's testsuite
(the FSF testsuite crashes all of AdaCore's solaris machines).
-rw-r--r-- | gdb/dwarf2-frame.c | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/gdb/dwarf2-frame.c b/gdb/dwarf2-frame.c index 199ccea..f2053f4 100644 --- a/gdb/dwarf2-frame.c +++ b/gdb/dwarf2-frame.c @@ -1510,12 +1510,12 @@ dwarf2_frame_cfa (struct frame_info *this_frame) throw_error (NOT_AVAILABLE_ERROR, _("can't compute CFA for this frame: " "required registers or memory are unavailable")); - /* This restriction could be lifted if other unwinders are known to - compute the frame base in a way compatible with the DWARF - unwinder. */ - if (!frame_unwinder_is (this_frame, &dwarf2_frame_unwind) - && !frame_unwinder_is (this_frame, &dwarf2_tailcall_frame_unwind)) - error (_("can't compute CFA for this frame")); + + if (get_frame_id (this_frame).stack_status != FID_STACK_VALID) + throw_error (NOT_AVAILABLE_ERROR, + _("can't compute CFA for this frame: " + "frame base not available")); + return get_frame_base (this_frame); } |