[PATCH v2] ARM64: reloc: fix relocation error for big fat bareboxes

[PATCH v2] ARM64: reloc: fix relocation error for big fat bareboxes

[Ahmad Fatoum]

A multi_v8 barebox with KASAN enabled is 2051804 bytes even after
compression and this breaks linking for me:

  arch/arm/cpu/common.o: in function `global_variable_offset':
  arch/arm/include/asm/reloc.h:20:(.text.relocate_to_current_adr+0x1c):
    relocation truncated to fit: R_AARCH64_ADR_PREL_LO21 against symbol
    `_text' defined in .text section in .tmp_barebox1
  arch/arm/include/asm/reloc.h:20:(.text.relocate_to_current_adr+0x40):
    relocation truncated to fit: R_AARCH64_ADR_PREL_LO21 against symbol
    `_text' defined in .text section in .tmp_barebox1

This is due to adr's limitation of only addressing bytes +/- 1 MiB from
the current PC. We have a solution for this in the form of the adr_l
macro, which we define for out-of-line assembly. Opencode this into the
inline assembly function, by using adrp to compute the page offset and
then add to arrive at the correct offset within the page.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
v1 -> v2:
  - fix typos: s/adrp/adr_l/, add unit (bytes) after barebox size
---
 arch/arm/include/asm/reloc.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/reloc.h b/arch/arm/include/asm/reloc.h
index 95b4ef0af88b..2d7411ab5284 100644
--- a/arch/arm/include/asm/reloc.h
+++ b/arch/arm/include/asm/reloc.h
@@ -18,7 +18,8 @@ static inline __prereloc unsigned long global_variable_offset(void)
 	unsigned long text;
 
 	__asm__ __volatile__(
-		"adr    %0, _text\n"
+		"adrp   %0, _text\n"
+		"add    %0, %0, :lo12:_text\n"
 		: "=r" (text)
 		:
 		: "memory");
-- 
2.39.2

Re: [PATCH v2] ARM64: reloc: fix relocation error for big fat bareboxes

[Sascha Hauer]

On Mon, 13 May 2024 16:01:21 +0200, Ahmad Fatoum wrote:
> A multi_v8 barebox with KASAN enabled is 2051804 bytes even after
> compression and this breaks linking for me:
> 
>   arch/arm/cpu/common.o: in function `global_variable_offset':
>   arch/arm/include/asm/reloc.h:20:(.text.relocate_to_current_adr+0x1c):
>     relocation truncated to fit: R_AARCH64_ADR_PREL_LO21 against symbol
>     `_text' defined in .text section in .tmp_barebox1
>   arch/arm/include/asm/reloc.h:20:(.text.relocate_to_current_adr+0x40):
>     relocation truncated to fit: R_AARCH64_ADR_PREL_LO21 against symbol
>     `_text' defined in .text section in .tmp_barebox1
> 
> [...]

Applied, thanks!

[1/1] ARM64: reloc: fix relocation error for big fat bareboxes
      https://git.pengutronix.de/cgit/barebox/commit/?id=9246c916a25a (link may not be stable)

Best regards,
-- 
Sascha Hauer <s.hauer@pengutronix.de>

Re: [PATCH v2] ARM64: reloc: fix relocation error for big fat bareboxes

[Ahmad Fatoum]

Hi,

On 15.05.24 07:55, Sascha Hauer wrote:
> 
> On Mon, 13 May 2024 16:01:21 +0200, Ahmad Fatoum wrote:
>> A multi_v8 barebox with KASAN enabled is 2051804 bytes even after
>> compression and this breaks linking for me:
>>
>>   arch/arm/cpu/common.o: in function `global_variable_offset':
>>   arch/arm/include/asm/reloc.h:20:(.text.relocate_to_current_adr+0x1c):
>>     relocation truncated to fit: R_AARCH64_ADR_PREL_LO21 against symbol
>>     `_text' defined in .text section in .tmp_barebox1
>>   arch/arm/include/asm/reloc.h:20:(.text.relocate_to_current_adr+0x40):
>>     relocation truncated to fit: R_AARCH64_ADR_PREL_LO21 against symbol
>>     `_text' defined in .text section in .tmp_barebox1
>>
>> [...]
> 
> Applied, thanks!

Thanks for applying. I thought some more about whether we should instead
have:

#ifdef __PBL__
        "adr    %0, _text\n"
#else
        /* (Decompressed) barebox proper should always be 4K aligned
         * so adrp here should be fine. PBL may also have adrp
         * references
         */
        "adrp   %0, _text\n"
        "add    %0, %0, :lo12:_text\n"
#endif

Otherwise, we require PBL to be placed 4K-aligned. Looking at GCC 13.2.1
output for an i.MX8M board, there are quite a lot of adrp references already,
so I think this shouldn't break anything that's not broken already anyway.

Just writing my thoughts for future reference.

Cheers,
Ahmad

> 
> [1/1] ARM64: reloc: fix relocation error for big fat bareboxes
>       https://git.pengutronix.de/cgit/barebox/commit/?id=9246c916a25a (link may not be stable)
> 
> Best regards,

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