[PATCH] riscv/kexec_file: Handle R_RISCV_64 in purgatory relocator

[PATCH] riscv/kexec_file: Handle R_RISCV_64 in purgatory relocator

[Yao Zi]

Commit 58ff537109ac ("riscv: Omit optimized string routines when
using KASAN") introduced calls to EXPORT_SYMBOL() in assembly string
routines, which result in R_RISCV_64 relocations against
.export_symbol section. As these rountines are reused by RISC-V
purgatory and our relocator doesn't recognize these relocations, this
fails kexec-file-load with dmesg like

	[   11.344251] kexec_image: Unknown rela relocation: 2
	[   11.345972] kexec_image: Error loading purgatory ret=-8

Let's support R_RISCV_64 relocation to fix kexec on 64-bit RISC-V.
32-bit variant isn't covered since KEXEC_FILE and KEXEC_PURGATORY isn't
available.

Fixes: 58ff537109ac ("riscv: Omit optimized string routines when using KASAN")
Signed-off-by: Yao Zi <ziyao@disroot.org>
---

I noticed RISC-V support hasn't been merged into kexec-tools, so this
patch is tested with this dowmstream branch[1].

Thanks for your time and review.

[1]: https://github.com/ziyao233/kexec-tools/tree/rv-Image

 arch/riscv/kernel/elf_kexec.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/riscv/kernel/elf_kexec.c b/arch/riscv/kernel/elf_kexec.c
index 3c37661801f9..e783a72d051f 100644
--- a/arch/riscv/kernel/elf_kexec.c
+++ b/arch/riscv/kernel/elf_kexec.c
@@ -468,6 +468,9 @@ int arch_kexec_apply_relocations_add(struct purgatory_info *pi,
 		case R_RISCV_ALIGN:
 		case R_RISCV_RELAX:
 			break;
+		case R_RISCV_64:
+			*(u64 *)loc = val;
+			break;
 		default:
 			pr_err("Unknown rela relocation: %d\n", r_type);
 			return -ENOEXEC;
-- 
2.49.0

Re: [PATCH] riscv/kexec_file: Handle R_RISCV_64 in purgatory relocator

[Björn Töpel]

Yao Zi <ziyao@disroot.org> writes:

> Commit 58ff537109ac ("riscv: Omit optimized string routines when
> using KASAN") introduced calls to EXPORT_SYMBOL() in assembly string
> routines, which result in R_RISCV_64 relocations against
> .export_symbol section. As these rountines are reused by RISC-V
> purgatory and our relocator doesn't recognize these relocations, this
> fails kexec-file-load with dmesg like
>
> 	[   11.344251] kexec_image: Unknown rela relocation: 2
> 	[   11.345972] kexec_image: Error loading purgatory ret=-8
>
> Let's support R_RISCV_64 relocation to fix kexec on 64-bit RISC-V.
> 32-bit variant isn't covered since KEXEC_FILE and KEXEC_PURGATORY isn't
> available.

Hi!

This patch does fix the vmlinux loading for kexec-file -- very nice!
However, I haven't been able to get kexec to successfully boot a kernel
from qemu, i.e.:

  kexec -s -l /path/to/vmlinux # fixed w/ your patch
  kexec -e # hangs after "Bye..."

Same when I try vanilla kexec (kexec -c -l /path/to/vmlinux). kexec with
an Image works for me in qemu.

Before I start to bisect too much; What config/qemu did you use to test
this?


Thanks,
Björn

Re: [PATCH] riscv/kexec_file: Handle R_RISCV_64 in purgatory relocator

[Björn Töpel]

Björn Töpel <bjorn@kernel.org> writes:

> Yao Zi <ziyao@disroot.org> writes:
>
>> Commit 58ff537109ac ("riscv: Omit optimized string routines when
>> using KASAN") introduced calls to EXPORT_SYMBOL() in assembly string
>> routines, which result in R_RISCV_64 relocations against
>> .export_symbol section. As these rountines are reused by RISC-V
>> purgatory and our relocator doesn't recognize these relocations, this
>> fails kexec-file-load with dmesg like
>>
>> 	[   11.344251] kexec_image: Unknown rela relocation: 2
>> 	[   11.345972] kexec_image: Error loading purgatory ret=-8
>>
>> Let's support R_RISCV_64 relocation to fix kexec on 64-bit RISC-V.
>> 32-bit variant isn't covered since KEXEC_FILE and KEXEC_PURGATORY isn't
>> available.
>
> Hi!
>
> This patch does fix the vmlinux loading for kexec-file -- very nice!
> However, I haven't been able to get kexec to successfully boot a kernel
> from qemu, i.e.:
>
>   kexec -s -l /path/to/vmlinux # fixed w/ your patch
>   kexec -e # hangs after "Bye..."
>
> Same when I try vanilla kexec (kexec -c -l /path/to/vmlinux). kexec with
> an Image works for me in qemu.
>
> Before I start to bisect too much; What config/qemu did you use to test
> this?

Nevermind! Got it to work; Sorry for the noise.

Tested-by: Björn Töpel <bjorn@rivosinc.com>
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>

Re: [PATCH] riscv/kexec_file: Handle R_RISCV_64 in purgatory relocator

[patchwork-bot+linux-riscv]

Hello:

This patch was applied to riscv/linux.git (for-next)
by Alexandre Ghiti <alexghiti@rivosinc.com>:

On Wed, 26 Mar 2025 05:14:46 +0000 you wrote:
> Commit 58ff537109ac ("riscv: Omit optimized string routines when
> using KASAN") introduced calls to EXPORT_SYMBOL() in assembly string
> routines, which result in R_RISCV_64 relocations against
> .export_symbol section. As these rountines are reused by RISC-V
> purgatory and our relocator doesn't recognize these relocations, this
> fails kexec-file-load with dmesg like
> 
> [...]

Here is the summary with links:
  - riscv/kexec_file: Handle R_RISCV_64 in purgatory relocator
    https://git.kernel.org/riscv/c/28093cfef5dd

You are awesome, thank you!
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