From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-lj1-x242.google.com ([2a00:1450:4864:20::242]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1h0sts-0004Uq-6t for barebox@lists.infradead.org; Mon, 04 Mar 2019 19:05:21 +0000 Received: by mail-lj1-x242.google.com with SMTP id v16so5266819ljg.13 for ; Mon, 04 Mar 2019 11:05:18 -0800 (PST) Date: Mon, 4 Mar 2019 22:05:06 +0300 From: Peter Mamonov Message-ID: <20190304190504.kmazotkohbssz2vn@chr> References: <20190218075202.10091-1-o.rempel@pengutronix.de> <20190218075202.10091-2-o.rempel@pengutronix.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190218075202.10091-2-o.rempel@pengutronix.de> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "barebox" Errors-To: barebox-bounces+u.kleine-koenig=pengutronix.de@lists.infradead.org Subject: Re: [PATCH v1 2/4] MIPS: relocation: add relocation support To: Oleksij Rempel Cc: antonypavlov@gmail.com, barebox@lists.infradead.org, Oleksij Rempel Hi, Oleksij, On Mon, Feb 18, 2019 at 08:52:00AM +0100, Oleksij Rempel wrote: > From: Oleksij Rempel > > this patch i a port of following patch from u-boot with some additional > integration changes and fixes of original code: > | Subject: [PATCH] MIPS: Stop building position independent code > | > | U-Boot has up until now built with -fpic for the MIPS architecture, > | producing position independent code which uses indirection through a > | global offset table, making relocation fairly straightforward as it > | simply involves patching up GOT entries. > | > | Using -fpic does however have some downsides. The biggest of these is > | that generated code is bloated in various ways. For example, function > | calls are indirected through the GOT & the t9 register: > | > | 8f998064 lw t9,-32668(gp) > | 0320f809 jalr t9 > | > | Without -fpic the call is simply: > | > | 0f803f01 jal be00fc04 > | > | This is more compact & faster (due to the lack of the load & the > | dependency the jump has on its result). It is also easier to read & > | debug because the disassembly shows what function is being called, > | rather than just an offset from gp which would then have to be looked up > | in the ELF to discover the target function. > | > | Another disadvantage of -fpic is that each function begins with a > | sequence to calculate the value of the gp register, for example: > | > | 3c1c0004 lui gp,0x4 > | 279c3384 addiu gp,gp,13188 > | 0399e021 addu gp,gp,t9 > | > | Without using -fpic this sequence no longer appears at the start of each > | function, reducing code size considerably. > | > | This patch switches U-Boot from building with -fpic to building with > | -fno-pic, in order to gain the benefits described above. The cost of > | this is an extra step during the build process to extract relocation > | data from the ELF & write it into a new .rel section in a compact > | format, plus the added complexity of dealing with multiple types of > | relocation rather than the single type that applied to the GOT. The > | benefit is smaller, cleaner, more debuggable code. The relocate_code() > | function is reimplemented in C to handle the new relocation scheme, > | which also makes it easier to read & debug. > | > | Taking maltael_defconfig as an example the size of u-boot.bin built > | using the Codescape MIPS 2016.05-06 toolchain (gcc 4.9.2, binutils > | 2.24.90) shrinks from 254KiB to 224KiB. > | > | Signed-off-by: Paul Burton > > Signed-off-by: Oleksij Rempel > --- > > [...] > > diff --git a/arch/mips/Makefile b/arch/mips/Makefile > index 5fbd51ceee..5eccf18fe4 100644 > --- a/arch/mips/Makefile > +++ b/arch/mips/Makefile > @@ -11,7 +11,7 @@ endif > > CPPFLAGS += -D__MIPS__ -fno-strict-aliasing -fno-merge-constants > > -cflags-y += -G 0 -mno-abicalls -fno-pic -pipe > +cflags-y += -G 0 -mno-abicalls -pipe The patch you've ported from das u-boot removes `-fpic` flag, yet your patch removes `-fno-pic`, i.e. it does the opposite thing. Regards, Peter _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox