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Re: [PATCH] PR gold/17640
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Cary Coutant <ccoutant at google dot com>
- Cc: Ilya Tocar <tocarip dot intel at gmail dot com>, Binutils <binutils at sourceware dot org>
- Date: Fri, 13 Mar 2015 11:55:34 -0700
- Subject: Re: [PATCH] PR gold/17640
- Authentication-results: sourceware.org; auth=none
- References: <CAMe9rOq-uSd64h6eeogR3SywtQipMupN9Ng9-EvPLF+3bp7Exw at mail dot gmail dot com> <20150305104052 dot GA16361 at msticlxl7 dot ims dot intel dot com> <CAMe9rOqRQ+HMS12+hn9Nz0pnb95tUDmbAU2QjK9G1Rc-q=woCA at mail dot gmail dot com> <20150310112745 dot GA104717 at msticlxl7 dot ims dot intel dot com> <CAMe9rOoG6NOVLYxZBJ5KRuS9_47=ptsd=Ft9iA9HfN2Asw0UeQ at mail dot gmail dot com> <20150312143236 dot GA95320 at msticlxl7 dot ims dot intel dot com> <CAMe9rOpn0uGDm1qbwgL-7CiYKjQeSHMHX6WzsnZ6eyfcp2MBAw at mail dot gmail dot com> <20150312145732 dot GB95320 at msticlxl7 dot ims dot intel dot com> <CAHACq4qF26jr8QYR_V55oVewLyHpgD2g7TrxDmgye0_S4pdroQ at mail dot gmail dot com> <CAMe9rOrMMxkR4bnoomCdW2P6TQtExMyMeC1oBHXNE3vXEEawLw at mail dot gmail dot com> <20150313112631 dot GA72598 at msticlxl7 dot ims dot intel dot com> <CAMe9rOqs=QROJZexdXKebsKrLrNat4mg=vgzuUrUpH1skpdTTQ at mail dot gmail dot com> <CAHACq4q761ontKOo3cr46hbo5dgi7A892GMB8rBBYuYwgY8ZKA at mail dot gmail dot com> <CAMe9rOq+MfTXB5k+8jgAxX+TMs=A-n4Fbu7hBG21kX9Wg7=7uA at mail dot gmail dot com> <CAHACq4p_351zLvX5dXjjxEjizTppm6sEgsCBCSiWdhntqpRx1w at mail dot gmail dot com>
On Fri, Mar 13, 2015 at 11:37 AM, Cary Coutant <ccoutant@google.com> wrote:
>>> You still haven't explained why we need to look for the symbol
>>> "_DYNAMIC" and treat it as a special case.
>>
>> This isn't the optimal code. Compiler may generate
>>
>> movl %eax, %edx
>> movl _DYNAMIC@GOT(%ecx), %eax
>> addl %edx, %eax
>>
>> instead of
>>
>> addl _DYNAMIC@GOT(%ecx), %eax
>>
>> I just want to be on the safe side.
>
> You're still not explaining. If the compiler generates that sequence,
> and we convert the mov to lea, why do we need the GOT entry?
>
LEA gives you the value after the program has bee loaded
to memory at run-time. But in ld.so before it has bootstrapped itself
movl _DYNAMIC@GOT(%ecx), %eax
gives you the link-time address, which what ld.so wants to bootstrap
itself.
--
H.J.