Re: [PATCH v3 5/8] sframe: Allow unsorted FDEs.

[Jens Remus <jremus@linux.ibm.com>]

On 4/6/2026 8:49 PM, Dylan Hatch wrote:
> The .sframe in kernel modules is built without SFRAME_F_FDE_SORTED set.
> In order to allow sframe PC lookup in modules, add a code path to handle
> unsorted FDE tables by doing a simple linear search.
> 
> Signed-off-by: Dylan Hatch <dylanbhatch@google.com>

With my below two minor comments considered:

Reviewed-by: Jens Remus <jremus@linux.ibm.com>

> diff --git a/include/linux/sframe.h b/include/linux/sframe.h

> @@ -64,6 +64,7 @@ struct sframe_section {
>  	unsigned long		text_start;
>  	unsigned long		text_end;
>  
> +	bool			fdes_sorted;
>  	unsigned long		fdes_start;
>  	unsigned long		fres_start;
>  	unsigned long		fres_end;

The struct would be smaller if the bool fdes_sorted flag would be
inserted after the unsigned int num_fdes field:

$ pahole -C sframe_section kernel/unwind/sframe.o

Yours:
size: 96

With bool fdes_sorted moved after unsigned int num_fdes:
size: 88

> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c

> @@ -179,9 +179,34 @@ static __always_inline int __read_fde(struct sframe_section *sec,
>  	return -EFAULT;
>  }
>  
> -static __always_inline int __find_fde(struct sframe_section *sec,
> -				      unsigned long ip,
> -				      struct sframe_fde_internal *fde)
> +static __always_inline int __find_fde_unsorted(struct sframe_section *sec,
> +					       unsigned long ip,
> +					       struct sframe_fde_internal *fde)
> +{
> +	struct sframe_fde_v3 *cur, *start, *end;
> +
> +	start = (struct sframe_fde_v3 *)sec->fdes_start;
> +	end = start + sec->num_fdes;
> +
> +	for (cur = start; cur < end; cur++) {
> +		s64 func_off;
> +		u32 func_size;
> +		unsigned long func_addr;
> +
> +		DATA_GET(sec, func_off, &cur->func_start_off, s64, Efault);
> +		DATA_GET(sec, func_size, &cur->func_size, u32, Efault);
> +		func_addr = (unsigned long)cur + func_off;
> +
> +		if (ip >= func_addr && ip < func_addr + func_size)
> +			return __read_fde(sec, cur - start, fde);
> +	}

__find_fde() (now __find_fde_sorted()) returns -EINVAL, if no FDE is found:

	return -EINVAL;

> +Efault:
> +	return -EFAULT;
> +}
Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com

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