[Bug debug/54793] New: the location of a formal_parameter is not started from a function entry with -mfentry

["masami.hiramatsu.pt at hitachi dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54793

             Bug #: 54793
           Summary: the location of a formal_parameter is not started from
                    a function entry with -mfentry
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: masami.hiramatsu.pt@hitachi.com


With -mfentry, GCC (I've found this with Red Hat 4.7.0-5 and
Red Hat 4.7.2-2 on Fedora 17) generates odd debuginfo about
variable locations.

Here are examples:
-----
 <1><9a58>: Abbrev Number: 86 (DW_TAG_subprogram)
    <9a59>   DW_AT_external    : 1
    <9a59>   DW_AT_name        : (indirect string, offset: 0xd82):
unregister_di
e_notifier
    <9a5d>   DW_AT_decl_file   : 1
    <9a5e>   DW_AT_decl_line   : 551
    <9a60>   DW_AT_prototyped  : 1
    <9a60>   DW_AT_type        : <0x7c>
    <9a64>   DW_AT_low_pc      : 0x740
    <9a6c>   DW_AT_high_pc     : 0x75a
    <9a74>   DW_AT_frame_base  : 1 byte block: 9c       (DW_OP_call_frame_cfa)
    <9a76>   DW_AT_GNU_all_call_sites: 1
    <9a76>   DW_AT_sibling     : <0x9aac>
 <2><9a7a>: Abbrev Number: 87 (DW_TAG_formal_parameter)
    <9a7b>   DW_AT_name        : nb
    <9a7e>   DW_AT_decl_file   : 1
    <9a7f>   DW_AT_decl_line   : 551
    <9a81>   DW_AT_type        : <0x2a96>
    <9a85>   DW_AT_location    : 0x172f (location list)
...
    0000172f 0000000000000745 0000000000000750 (DW_OP_reg5 (rdi))
    0000172f 0000000000000750 0000000000000757 (DW_OP_reg4 (rsi))
    0000172f 0000000000000757 000000000000075a (DW_OP_GNU_entry_value:
(DW_OP_reg5 (rdi)); DW_OP_stack_value)
    0000172f <End of list>
-----
As you can see, the location of the parameter "nb", starts from 0x745
but unregister_die_notifier() function itself starts from 0x740.

-----
 <1><9aac>: Abbrev Number: 86 (DW_TAG_subprogram)
    <9aad>   DW_AT_external    : 1
    <9aad>   DW_AT_name        : (indirect string, offset: 0x321f): notify_die
    <9ab1>   DW_AT_decl_file   : 1
    <9ab2>   DW_AT_decl_line   : 530
    <9ab4>   DW_AT_prototyped  : 1
    <9ab4>   DW_AT_type        : <0x7c>
    <9ab8>   DW_AT_low_pc      : 0xb0
    <9ac0>   DW_AT_high_pc     : 0xe0
    <9ac8>   DW_AT_frame_base  : 1 byte block: 9c       (DW_OP_call_frame_cfa)
    <9aca>   DW_AT_GNU_all_call_sites: 1
    <9aca>   DW_AT_sibling     : <0x9b6c>
 <2><9ace>: Abbrev Number: 87 (DW_TAG_formal_parameter)
    <9acf>   DW_AT_name        : val
    <9ad3>   DW_AT_decl_file   : 1
    <9ad4>   DW_AT_decl_line   : 530
    <9ad6>   DW_AT_type        : <0x2b36>
    <9ada>   DW_AT_location    : 0x177b (location list)
...
    0000177b 00000000000000b0 00000000000000cd (DW_OP_reg5 (rdi))
    0000177b 00000000000000cd 00000000000000dd (DW_OP_reg4 (rsi))
    0000177b 00000000000000dd 00000000000000e0 (DW_OP_GNU_entry_value:
(DW_OP_reg5 (rdi)); DW_OP_stack_value)
    0000177b <End of list>
-----
However, without fentry call (notifiy_die is marked notrace),
the parameter "val" location start with 0xb0, which is same as
notify_die start address.


URL: https://lkml.org/lkml/2012/10/3/187