From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-pg1-x542.google.com ([2607:f8b0:4864:20::542]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1goeiV-0004RO-Qf for barebox@lists.infradead.org; Wed, 30 Jan 2019 01:31:05 +0000 Received: by mail-pg1-x542.google.com with SMTP id t13so9577543pgr.11 for ; Tue, 29 Jan 2019 17:31:03 -0800 (PST) From: Andrey Smirnov Date: Tue, 29 Jan 2019 17:30:50 -0800 Message-Id: <20190130013050.3834-1-andrew.smirnov@gmail.com> MIME-Version: 1.0 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: [PATCH v2] ARM: aarch64: Avoid relocations in runtime-offset.S To: barebox@lists.infradead.org Cc: Andrey Smirnov Since get_runtime_offset() is executed as a part of reloaction logic, it cannot have code dependend on any kind of relocation. Unfortunately, current codebase violates this rule and linkadr: .quad get_runtime_offset ends up producing R_AARCH64_RELATIVE relocation that has to be resolved at runtime. From tiral and error experimentation it seems that the simplest way to do this is to drop "a" (allocatable) attribute fom the section directive in runtime-offset.S With "a" (see first entry): aarch64-linux-gnu-objdump -R images/start_zii_imx8mq_dev.pbl images/start_zii_imx8mq_dev.pbl: file format elf64-littleaarch64 DYNAMIC RELOCATION RECORDS OFFSET TYPE VALUE 00000000000000b0 R_AARCH64_RELATIVE *ABS*+0x00000000000000a0 0000000000004258 R_AARCH64_RELATIVE *ABS*+0x0000000000028118 0000000000004260 R_AARCH64_RELATIVE *ABS*+0x0000000000028128 00000000000042e0 R_AARCH64_RELATIVE *ABS* 00000000000042e8 R_AARCH64_RELATIVE *ABS*+0x0000000000028118 00000000000042f0 R_AARCH64_RELATIVE *ABS*+0x00000000000042c8 Without "a": aarch64-linux-gnu-objdump -R images/start_zii_imx8mq_dev.pbl images/start_zii_imx8mq_dev.pbl: file format elf64-littleaarch64 DYNAMIC RELOCATION RECORDS OFFSET TYPE VALUE 0000000000004258 R_AARCH64_RELATIVE *ABS*+0x0000000000028100 0000000000004260 R_AARCH64_RELATIVE *ABS*+0x0000000000028110 00000000000042e0 R_AARCH64_RELATIVE *ABS* 00000000000042e8 R_AARCH64_RELATIVE *ABS*+0x0000000000028100 00000000000042f0 R_AARCH64_RELATIVE *ABS*+0x00000000000042c8 Note that on recent toolchains (tested on 8.1.1), this problem is masked by the fact that .quad get_runtime_offset will be initialized with link-time value of "get_runtime_offset" in addition to having a R_AARCH64_RELATIVE relocation. 00000000000000a0 : a0: 10000000 adr x0, a0 a4: 58000061 ldr x1, b0 a8: eb010000 subs x0, x0, x1 ac: d65f03c0 ret 00000000000000b0 : b0: 000000a0 .word 0x000000a0 b4: 00000000 .word 0x00000000 _However_, older toolchains (tested on 5.5.0), will only issue a R_AARCH64_RELATIVE, so memory location will contain only zeroes: 00000000000000a0 : a0: 10000000 adr x0, a0 a4: 58000061 ldr x1, b0 a8: eb010000 subs x0, x0, x1 ac: d65f03c0 ret 00000000000000b0 : ... This leads to an very early crash and complete boot failure in the latter case. Signed-off-by: Andrey Smirnov --- Changes since [v1]: - Added a comment explaining the reasoning "a" specifier is missing [v1] http://lists.infradead.org/pipermail/barebox/2019-January/036779.html arch/arm/lib64/runtime-offset.S | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/arch/arm/lib64/runtime-offset.S b/arch/arm/lib64/runtime-offset.S index 177ca6478..6624fdfa1 100644 --- a/arch/arm/lib64/runtime-offset.S +++ b/arch/arm/lib64/runtime-offset.S @@ -1,7 +1,19 @@ #include #include -.section ".text_bare_init","ax" +/* + * The .section directive below intentionally omits "a", since that + * appears to be the simplest way to force assembler to not generate + * R_AARCH64_RELATIVE relocation for + * + * linkadr: + * .quad get_runtime_offset + * + * statement below. While having that relocating was relatively + * harmless with GCC8, builging the code with GCC5 resulted in + * "linkaddr" being initialized to 0 causing complete boot breakdown + */ +.section ".text_bare_init","x" /* * Get the offset between the link address and the address -- 2.20.1 _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox