On 9/3/20 1:07 PM, Edgar E. Iglesias wrote: > On Thu, Sep 03, 2020 at 09:45:39AM -0600, Stephen Warren wrote: >> On 9/3/20 7:40 AM, André Przywara wrote: >>> On 03/09/2020 14:35, Michal Simek wrote: >>>> >>>> >>>> On 02. 09. 20 18:34, Stephen Warren wrote: >>>>> On 9/2/20 5:15 AM, Michal Simek wrote: >>>>>> From: "Edgar E. Iglesias" <edgar.igles...@xilinx.com> >>>>>> >>>>>> When U-Boot binary exceeds 1MB with CONFIG_POSITION_INDEPENDENT=y >>>>>> compilation error is shown: >>>>>> /mnt/disk/u-boot/arch/arm/cpu/armv8/start.S:71:(.text+0x3c): relocation >>>>>> truncated to fit: R_AARCH64_ADR_PREL_LO21 against symbol `__rel_dyn_end' >>>>>> defined in .bss_start section in u-boot. >>>>>> >>>>>> It is caused by adr instruction which permits the calculation of any byte >>>>>> address within +- 1MB of the current PC. >>>>>> Because U-Boot is bigger then 1MB calculation is failing. >>>>>> >>>>>> The patch is using adrp/add instructions where adrp shifts a signed, >>>>>> 21-bit >>>>>> immediate left by 12 bits (4k page), adds it to the value of the program >>>>>> counter with the bottom 12 bits cleared to zero. Then add instruction >>>>>> provides the lower 12 bits which is offset within 4k page. >>>>>> These two instructions together compose full 32bit offset which should be >>>>>> more then enough to cover the whole u-boot size. >>>>> >>>>>> diff --git a/arch/arm/cpu/armv8/start.S b/arch/arm/cpu/armv8/start.S >>>>> >>>>>> @@ -67,8 +67,10 @@ pie_fixup: >>>>>> adr x0, _start /* x0 <- Runtime value of >>>>>> _start */ >>>>>> ldr x1, _TEXT_BASE /* x1 <- Linked value of _start >>>>>> */ >>>>>> sub x9, x0, x1 /* x9 <- Run-vs-link offset */ >>>>>> - adr x2, __rel_dyn_start /* x2 <- Runtime >>>>>> &__rel_dyn_start */ >>>>>> - adr x3, __rel_dyn_end /* x3 <- Runtime &__rel_dyn_end >>>>>> */ >>>>>> + adrp x2, __rel_dyn_start /* x2 <- Runtime >>>>>> &__rel_dyn_start */ >>>>>> + add x2, x2, #:lo12:__rel_dyn_start >>>>>> + adrp x3, __rel_dyn_end /* x3 <- Runtime &__rel_dyn_end >>>>>> */ >>>>>> + add x3, x3, #:lo12:__rel_dyn_end >>>>>> pie_fix_loop: >>>>>> ldp x0, x1, [x2], #16 /* (x0, x1) <- (Link location, >>>>>> fixup) */ >>>>>> ldr x4, [x2], #8 /* x4 <- addend */ >>>>> >>>>> There are likely a bunch of other places in the code that need updating >>>>> too; take a look at commit 49e93875a62f "arm64: support running at addr >>>>> other than linked to" (which introduced the code above) to find other >>>>> places with similar instruction sequences that almost certainly need >>>>> updating. >>>>> >>>> >>>> I didn't hit any issue to have a need to update them. Definitely worth >>>> to check that locations too. >>> >>> So I thought the same, so I checked at least this file. And while there >>> are other "adr" instructions, they only go to nearby labels, so don't >>> need to be pumped up. >>> But I will try to grep for more cases as well. >> >> >> So in the patch I linked to, what about the added ard instructions in >> arch/arm/lib/crt0_64.S and arch/arm/lib/relocate_64.S? >> >> Perhaps that code gets linked more towards the middle of U-Boot than the >> code you're fixing in start.S, so the max 1M offset just happens to >> reach all the relevant symbols and relocations that are in your current >> binary, but if your binary gets a little larger (e.g. goes from 1.05M to >> 2M say) that code will fail in the same way? > > Yes, those were apparently already corrected by Ibai: > https://github.com/u-boot/u-boot/commit/98ffbb78e12646a1d06236ad6a1893217f255aae#diff-4f864f65dc6b6f2535a5d252b7c9fcc7
Ah OK. So I guess this means that in practice, U-Boot already has the limitation that the load (and relocation target?) address must be 4K-aligned, since it uses the same instruction sequence we're discusssing here.
