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From: "Marek Behún" <marek.behun@nic.cz>
To: u-boot@lists.denx.de
Subject: [RFC PATCH u-boot 09/12] ARM: make gd a function for LTO
Date: Wed,  3 Mar 2021 05:12:08 +0100	[thread overview]
Message-ID: <20210303041211.26945-10-marek.behun@nic.cz> (raw)
In-Reply-To: <20210303041211.26945-1-marek.behun@nic.cz>

On ARM the gd pointer is stored in registers r9 / x18. For this the
-ffixed-r9 / -ffixed-x18 flag when compiling, but using global register
variables causes errors when building with LTO, and these errors are
very difficult to overcome.

Richard Biener says [1]:
  Note that global register vars shouldn't be used with LTO and if they
  are restricted to just a few compilation units the recommended fix is
  to build those CUs without -flto.

We cannot do this for U-Boot since all CUs use -ffixed-reg flag.

It seems that with LTO we could in fact store the gd pointer differently
and gain performance or size benefit by allowing the compiler to use
r9 / x18. But this would need more work.

So for now, when building with LTO, go the clang way, and instead of
declaring gd a global register variable we make it a function via macro.

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68384

Signed-off-by: Marek Beh?n <marek.behun@nic.cz>
---
 arch/arm/include/asm/global_data.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/global_data.h b/arch/arm/include/asm/global_data.h
index fba655f3b9..d694074bff 100644
--- a/arch/arm/include/asm/global_data.h
+++ b/arch/arm/include/asm/global_data.h
@@ -91,7 +91,7 @@ struct arch_global_data {
 
 #include <asm-generic/global_data.h>
 
-#ifdef __clang__
+#if defined(__clang__) || defined(CONFIG_LTO)
 
 #define DECLARE_GLOBAL_DATA_PTR
 #define gd	get_gd()
-- 
2.26.2

  parent reply	other threads:[~2021-03-03  4:12 UTC|newest]

Thread overview: 75+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-03  4:11 [RFC PATCH u-boot 00/12] U-Boot LTO (Sandbox + ARM Nokia RX-51) Marek Behún
2021-03-03  4:12 ` [RFC PATCH u-boot 01/12] build: use thin archives instead of incremental linking Marek Behún
2021-03-04 10:57   ` Bin Meng
2021-03-04 18:17     ` Marek Behun
2021-03-05 13:34       ` Bin Meng
2021-03-05 13:37         ` Tom Rini
2021-03-06 21:20           ` Marek Behun
2021-03-05 15:39         ` Marek Behun
2021-03-03  4:12 ` [RFC PATCH u-boot 02/12] sandbox: errno: avoid conflict with libc's errno Marek Behún
2021-03-05  3:00   ` Bin Meng
2021-03-05 15:37     ` Marek Behun
2021-03-05 16:39       ` Simon Glass
2021-03-05 16:50         ` Marek Behun
2021-03-05 16:58           ` Simon Glass
2021-03-05 17:24             ` Heinrich Schuchardt
2021-03-05 17:24             ` Marek Behun
2021-03-05 19:42               ` Simon Glass
2021-03-05 17:21       ` Heinrich Schuchardt
2021-03-07  3:14         ` Marek Behun
2021-03-12  4:45   ` Simon Glass
2021-03-03  4:12 ` [RFC PATCH u-boot 03/12] linker_lists: declare entries and lists externally visible Marek Behún
2021-03-04 13:47   ` Marek Behun
2021-03-05  3:04   ` Bin Meng
2021-03-05 15:49     ` Marek Behun
2021-03-03  4:12 ` [RFC PATCH u-boot 04/12] efi_loader: fix warning when linking with LTO Marek Behún
2021-03-05  5:50   ` Bin Meng
2021-03-03  4:12 ` [RFC PATCH u-boot 05/12] binman: declare symbols externally visible Marek Behún
2021-03-04  0:37   ` Tom Rini
2021-03-04  1:53     ` Marek Behun
2021-03-03  4:12 ` [RFC PATCH u-boot 06/12] build: support building with Link Time Optimizations Marek Behún
2021-03-05  6:34   ` Bin Meng
2021-03-03  4:12 ` [RFC PATCH u-boot 07/12] arch: sandbox: make LTO available Marek Behún
2021-03-03  4:12 ` [RFC PATCH u-boot 08/12] sandbox: build with LTO Marek Behún
2021-03-03  4:12 ` Marek Behún [this message]
2021-03-03  4:12 ` [RFC PATCH u-boot 10/12] string: make memcpy() visible to fix LTO linking errors Marek Behún
2021-03-03  4:12 ` [RFC PATCH u-boot 11/12] arch: ARM: make LTO available Marek Behún
2021-03-03  4:12 ` [RFC PATCH u-boot 12/12] Nokia RX-51: build with LTO Marek Behún
2021-03-03 16:11 ` [RFC PATCH u-boot 00/12] U-Boot LTO (Sandbox + ARM Nokia RX-51) Tom Rini
2021-03-03 16:41   ` Marek Behun
2021-03-03 16:47     ` Tom Rini
2021-03-03 21:36     ` Tom Rini
2021-03-04  0:40       ` Adam Ford
2021-03-04  7:07         ` [PATCH] arm: fix LTO build for some thumb-interwork cases Marek Behún
2021-03-04 10:43       ` [RFC PATCH u-boot 00/12] U-Boot LTO (Sandbox + ARM Nokia RX-51) Marek Behun
2021-03-04 13:46         ` Adam Ford
2021-03-04 13:50           ` Marek Behun
2021-03-04 13:59             ` Adam Ford
2021-03-04 14:58           ` Tom Rini
2021-03-04 15:07             ` Adam Ford
2021-03-04 15:37               ` Marek Behun
2021-03-04 16:18                 ` Tom Rini
2021-03-04 15:59               ` Marek Behun
2021-03-04 22:18                 ` Adam Ford
2021-03-04 22:33                   ` Marek Behun
2021-03-05 11:25                     ` Adam Ford
2021-03-05 12:31                       ` Stefan Roese
2021-03-05 17:10                         ` Adam Ford
2021-03-06  3:03                           ` Adam Ford
2021-03-06 11:12                             ` Adam Ford
2021-03-06 17:37                               ` Marek Behun
2021-03-06 20:08                                 ` Tom Rini
2021-03-06 20:41                                   ` Pali Rohár
2021-03-06 20:54                                     ` Marek Behun
2021-03-06 21:00                                       ` Pali Rohár
2021-03-06 21:19                                         ` Marek Behun
2021-03-06 21:38                                           ` Pali Rohár
2021-03-06 21:49                                             ` Marek Behun
2021-03-07  3:45                                               ` Adam Ford
2021-03-07  4:06                                                 ` Marek Behun
2021-05-09 14:14                                                   ` Adam Ford
2021-05-09 18:44                                                     ` Marek Behun
2021-05-10 16:28                                                       ` Simon Glass
2021-05-13  9:22                                                         ` Pali Rohár
2021-03-04 16:17               ` Tom Rini
2021-03-04 16:35                 ` Pali Rohár

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