The unwind info is wrong for any instruction-pointer (IP) in the epilog after
the point at which the stack-pointer has been popped. For example:
0000000000400758 <func>:
400758: 48 89 5c 24 d8 mov %rbx,0xffffffffffffffd8(%rsp)
40075d: 48 89 6c 24 e0 mov %rbp,0xffffffffffffffe0(%rsp)
400762: 4c 89 64 24 e8 mov %r12,0xffffffffffffffe8(%rsp)
400767: 4c 89 6c 24 f0 mov %r13,0xfffffffffffffff0(%rsp)
40076c: 4c 89 74 24 f8 mov %r14,0xfffffffffffffff8(%rsp)
400771: 48 81 ec 28 10 00 00 sub $0x1028,%rsp
:
40081c: 48 81 c4 28 10 00 00 add $0x1028,%rsp
400823: c3 retq
The unwind-info for this function looks like this:
00000018 00000024 0000001c FDE cie=00000000 pc=00400758..00400824
DW_CFA_advance_loc: 32 to 00400778
DW_CFA_def_cfa_offset: 4144
DW_CFA_offset: r14 at cfa-16
DW_CFA_offset: r13 at cfa-24
DW_CFA_offset: r12 at cfa-32
DW_CFA_offset: r6 at cfa-40
DW_CFA_offset: r3 at cfa-48
Note that there is no indication that the stack gets restored in the second-last
instruction, hence it is impossible to unwind when IP = 0x400823.
--
Summary: GCC fails to mark stack-popping instruction in unwind-
info
Product: gcc
Version: 3.3.3
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: davidm at hpl dot hp dot com
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: x86_64-suse-linux
GCC host triplet: x86_64-suse-linux
GCC target triplet: x86_64-suse-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18749
