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Date: Sun, 25 Jan 2015 12:41:00 -0000
From: Jan Kratochvil <jan.kratochvil@redhat.com>
To: Doug Evans <xdje42@gmail.com>
Cc: Jonathan Larmour <jifl@eCosCentric.com>, gdb@sourceware.org
Subject: Re: dwarf_block_to_fb_offset() and 64-bit host
Message-ID: <20150125083241.GB5745@host1.jankratochvil.net>
References: <54C48488.6040100@eCosCentric.com> <m38ugr9tre.fsf@sspiff.org>
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On Sun, 25 Jan 2015 08:58:13 +0100, Doug Evans wrote:
> I guess the first question is: Is an fb_offset of -28 valid?
> i.e., is a negative value valid?

It should not be for decreasing-sp archs (like x86*):

gdb.arch/amd64-entry-value:
 <3><a90>: Abbrev Number: 8 (DW_TAG_GNU_call_site_parameter)
    <a91>   DW_AT_location    : 2 byte block: 77 0      (DW_OP_breg7 (rsp): 0)
                                                                            ^
    <a94>   DW_AT_GNU_call_site_value: 1 byte block: 3b         (DW_OP_lit11)
 <3><a96>: Abbrev Number: 8 (DW_TAG_GNU_call_site_parameter)
    <a97>   DW_AT_location    : 2 byte block: 77 8      (DW_OP_breg7 (rsp): 8)
                                                                            ^
    <a9a>   DW_AT_GNU_call_site_value: 1 byte block: 3c         (DW_OP_lit12)
 <3><a9c>: Abbrev Number: 8 (DW_TAG_GNU_call_site_parameter)
    <a9d>   DW_AT_location    : 2 byte block: 77 10     (DW_OP_breg7 (rsp): 16)
                                                                            ^^
    <aa0>   DW_AT_GNU_call_site_value: 11 byte block: f4 31 8 0 0 0 0 0 0 27 40         (DW_OP_GNU_const_type: <0x31>  8 byte block: 0 0 0 0 0 0 27 40 )
 <3><aac>: Abbrev Number: 8 (DW_TAG_GNU_call_site_parameter)
    <aad>   DW_AT_location    : 2 byte block: 77 18     (DW_OP_breg7 (rsp): 24)
                                                                            ^^
    <ab0>   DW_AT_GNU_call_site_value: 11 byte block: f4 31 8 0 0 0 0 0 0 29 40         (DW_OP_GNU_const_type: <0x31>  8 byte block: 0 0 0 0 0 0 29 40 )

Despite its 'fb_offset' name it is an offset from SP so parameters should not
be stored in the to-be-rewritten area under SP.



Jan