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Re: [PATCH] Expand PIC calls without PLT with -fno-plt

From: Jeff Law <law at redhat dot com>
To: Jakub Jelinek <jakub at redhat dot com>
Cc: Alexander Monakov <amonakov at ispras dot ru>, gcc-patches at gcc dot gnu dot org, Rich Felker <dalias at libc dot org>
Date: Mon, 04 May 2015 11:42:20 -0600
Subject: Re: [PATCH] Expand PIC calls without PLT with -fno-plt
Authentication-results: sourceware.org; auth=none
References: <1430757479-14241-1-git-send-email-amonakov at ispras dot ru> <1430757479-14241-6-git-send-email-amonakov at ispras dot ru> <5547AD8D dot 9080806 at redhat dot com> <20150504173955 dot GE1751 at tucnak dot redhat dot com>

On 05/04/2015 11:39 AM, Jakub Jelinek wrote:

On Mon, May 04, 2015 at 11:34:05AM -0600, Jeff Law wrote:

On 05/04/2015 10:37 AM, Alexander Monakov wrote:

This patch introduces option -fno-plt that allows to expand calls that would
go via PLT to load the address of the function immediately at call site (which
introduces a GOT load).  Cover letter explains the motivation for this patch.

New option documentation for invoke.texi is missing from the patch; if this is
accepted I'll be happy to send a v2 with documentation added.

	* calls.c (prepare_call_address): Transform PLT call to GOT lookup and
	indirect call by forcing address into a pseudo with -fno-plt.
	* common.opt (flag_plt): New option.

OK once you cobble together the invoke.texi changes.


Isn't what Michael/Alan suggested better?  I mean as/ld/compiler changes to
inline the plt slot's first part, then lazy binding will work fine.

I must have missed Alan/Michael's message.

ISTM the win here is that by going through the GOT, you can CSE the GOTreference and possibly get some more register allocation freedom. Isthat still the case with Alan/Michael's approach?


jeff

Follow-Ups:
- Re: [PATCH] Expand PIC calls without PLT with -fno-plt
  - From: Rich Felker
- Re: [PATCH] Expand PIC calls without PLT with -fno-plt
  - From: Alexander Monakov

References:
- PIC calls without PLT, generic implementation
  - From: Alexander Monakov
- [PATCH] Expand PIC calls without PLT with -fno-plt
  - From: Alexander Monakov
- Re: [PATCH] Expand PIC calls without PLT with -fno-plt
  - From: Jeff Law
- Re: [PATCH] Expand PIC calls without PLT with -fno-plt
  - From: Jakub Jelinek

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