Re: [PATCH v5 6/8] arm64/module, sframe: Add sframe support for modules

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

On 4/28/2026 8:36 PM, Dylan Hatch wrote:
> Add sframe table to mod_arch_specific and support sframe PC lookups when
> an .sframe section can be found on incoming modules.
One small fix and a proposal to sort the module's SFrame FDE index.

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

A subsequent patch adds a call to sframe_validate_section(), which would
operate on the temporary struct sframe_section instance and thus fail
to use container_of() to access the struct module instance.  To resolve
change as follows:

> +void sframe_module_init(struct module *mod, void *sframe, size_t sframe_size,
> +			void *text, size_t text_size)
> +{
> +	struct sframe_section sec;

	struct sframe_section *sec = &mod->arch.sframe_sec;

It is fine to initialize the module's struct sframe_section instance as
use of the information is guarded by mod->arch.sframe_init, which is
only set if the instance has been full initialized.

> +
> +	memset(&sec, 0, sizeof(sec));

Can be dropped if struct module instance got zero-initialized.

> +	sec.sec_type	 = SFRAME_KERNEL;
> +	sec.sframe_start = (unsigned long)sframe;
> +	sec.sframe_end   = (unsigned long)sframe + sframe_size;
> +	sec.text_start   = (unsigned long)text;
> +	sec.text_end     = (unsigned long)text + text_size;

Adjust all lines above to pointer access.

> +
> +	if (WARN_ON(sframe_read_header(&sec)))

Ditto.

> +		return;
> +
> +	mod->arch.sframe_sec = sec;

Drop.

> +	mod->arch.sframe_init = true;
> +}
Indu suggested that it would be preferable if a module's .sframe FDE
index table could be sorted during loading of the module to enable
binary search instead of having to resort to linear search.  I propose
to change this patch as follows to sort the module .sframe FDE index
table in sframe_module_init().  Note that the patch assumes above
changes have been implemented.  The sorting is very similar to sorting
of ORC tables in arch/x86/kernel/unwind_orc.c in unwind_module_init().

diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -12,6 +12,7 @@
 #include <linux/mm.h>
 #include <linux/string_helpers.h>
 #include <linux/sframe.h>
+#include <linux/sort.h>
 #include <linux/unwind_types.h>
 #include <asm/unwind_sframe.h>
 #ifdef CONFIG_HAVE_UNWIND_KERNEL_SFRAME
@@ -1038,6 +1039,50 @@ void __init init_sframe_table(void)
 	sframe_init = true;
 }
 
+static int sframe_sort_cmp_fde(const void *a, const void *b)
+{
+	const struct sframe_fde_v3 *fde_a = a, *fde_b = b;
+	unsigned long func_start_a, func_start_b;
+
+	func_start_a = (unsigned long)fde_a + fde_a->func_start_off;
+	func_start_b = (unsigned long)fde_b + fde_b->func_start_off;
+
+	return cmp_int(func_start_a, func_start_b);
+}
+
+static void sframe_sort_swap_fde(void *a, void *b, int size)
+{
+	struct sframe_fde_v3 *fde_a = a, *fde_b = b;
+	struct sframe_fde_v3 temp;
+	long delta;
+
+	/* Swap potentially unaligned FDE */
+	memcpy(&temp, fde_a, sizeof(struct sframe_fde_v3));
+	memcpy(fde_a, fde_b, sizeof(struct sframe_fde_v3));
+	memcpy(fde_b, &temp, sizeof(struct sframe_fde_v3));
+
+	/* Adjust FDE function start offset from FDE */
+	delta = (long)((unsigned long)fde_b - (unsigned long)fde_a);
+	fde_a->func_start_off += delta;
+	fde_b->func_start_off -= delta;
+}
+
+static int sframe_sort_fdes(struct sframe_section *sec)
+{
+	void *fdes = (void *)sec->fdes_start;
+	size_t num_fdes = sec->num_fdes;
+
+	if (sec->sec_type != SFRAME_KERNEL)
+		return -EINVAL;
+	if (sec->fdes_sorted)
+		return 0;
+
+	sort(fdes, num_fdes, sizeof(struct sframe_fde_v3),
+	     sframe_sort_cmp_fde, sframe_sort_swap_fde);
+	sec->fdes_sorted = true;
+	return 0;
+}
+
 void sframe_module_init(struct module *mod, void *sframe, size_t sframe_size,
 			void *text, size_t text_size)
 {
@@ -1053,6 +1098,8 @@ void sframe_module_init(struct module *mod, void *sframe, size_t sframe_size,
 
 	if (WARN_ON(sframe_read_header(sec)))
 		return;
+	if (WARN_ON(sframe_sort_fdes(sec)))
+		return;
 	if (WARN_ON(sframe_validate_section(sec)))
 		return;
 
Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com

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