Hi Andrey, On Wed, Jan 23, 2019 at 07:15:43PM -0800, Andrey Smirnov wrote: > 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 <get_runtime_offset>: > a0: 10000000 adr x0, a0 <get_runtime_offset> > a4: 58000061 ldr x1, b0 <linkadr> > a8: eb010000 subs x0, x0, x1 > ac: d65f03c0 ret > > 00000000000000b0 <linkadr>: > 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 <get_runtime_offset>: > a0: 10000000 adr x0, a0 <get_runtime_offset> > a4: 58000061 ldr x1, b0 <linkadr> > a8: eb010000 subs x0, x0, x1 > ac: d65f03c0 ret > > 00000000000000b0 <linkadr>: > ... > > This leads to an very early crash and complete boot failure in the > latter case. I can reproduce this issue here. As you can imagine I do not really like this "fix". I have no idea what the proper solution is (other than deprecating gcc5), so I am fine removing the "a" flag as you suggested. I think though that we should add a big comment above this function *why* this lacks the "a" flag and that we can add it back once gcc5 is retired. Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
