[PATCH] arm64: Add support for bigger u-boot when CONFIG_POSITION_INDEPENDENT=y
Stephen Warren
swarren at wwwdotorg.org
Wed Sep 2 18:34:20 CEST 2020
On 9/2/20 5:15 AM, Michal Simek wrote:
> From: "Edgar E. Iglesias" <edgar.iglesias at 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.
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