[PATCH v4 25/39] unwind_user/sframe: Show file name in debug output

Josh Poimboeuf
2025-01-22T02:32:18Z

When debugging sframe issues, the error messages aren't all that helpful
without knowing what file a corresponding .sframe section belongs to.
Prefix debug output strings with the file name.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
include/linux/sframe.h | 4 +++-
kernel/unwind/sframe.c | 23 ++++++++++++--------
kernel/unwind/sframe_debug.h | 41 ++++++++++++++++++++++++++++++------
3 files changed, 52 insertions(+), 16 deletions(-)

diff --git a/include/linux/sframe.h b/include/linux/sframe.h
index 2e70085a1e89..18a04d574090 100644
--- a/include/linux/sframe.h
+++ b/include/linux/sframe.h
@@ -10,7 +10,9 @@

struct sframe_section {
struct rcu_head rcu;
-
+#ifdef CONFIG_DYNAMIC_DEBUG
+ const char *filename;
+#endif
unsigned long sframe_start;
unsigned long sframe_end;
unsigned long text_start;
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 66b920441692..f463123f9afe 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -295,14 +295,17 @@ int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
end:
user_read_access_end();

- if (ret == -EFAULT)
+ if (ret == -EFAULT) {
+ dbg_sec("removing bad .sframe section\n");
WARN_ON_ONCE(sframe_remove_section(sec->sframe_start));
+ }

return ret;
}

static void free_section(struct sframe_section *sec)
{
+ dbg_free(sec);
kfree(sec);
}

@@ -313,7 +316,7 @@ static int sframe_read_header(struct sframe_section *sec)
unsigned int num_fdes;

if (copy_from_user(&shdr, (void __user *)sec->sframe_start, sizeof(shdr))) {
- dbg("header usercopy failed\n");
+ dbg_sec("header usercopy failed\n");
return -EFAULT;
}

@@ -321,18 +324,18 @@ static int sframe_read_header(struct sframe_section *sec)
shdr.preamble.version != SFRAME_VERSION_2 ||
!(shdr.preamble.flags & SFRAME_F_FDE_SORTED) ||
shdr.auxhdr_len) {
- dbg("bad/unsupported sframe header\n");
+ dbg_sec("bad/unsupported sframe header\n");
return -EINVAL;
}

if (!shdr.num_fdes || !shdr.num_fres) {
- dbg("no fde/fre entries\n");
+ dbg_sec("no fde/fre entries\n");
return -EINVAL;
}

header_end = sec->sframe_start + SFRAME_HEADER_SIZE(shdr);
if (header_end >= sec->sframe_end) {
- dbg("header doesn't fit in section\n");
+ dbg_sec("header doesn't fit in section\n");
return -EINVAL;
}

@@ -344,7 +347,7 @@ static int sframe_read_header(struct sframe_section *sec)
fres_end = fres_start + shdr.fre_len;

if (fres_start < fdes_end || fres_end > sec->sframe_end) {
- dbg("inconsistent fde/fre offsets\n");
+ dbg_sec("inconsistent fde/fre offsets\n");
return -EINVAL;
}

@@ -400,6 +403,8 @@ int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
sec->text_start = text_start;
sec->text_end = text_end;

+ dbg_init(sec);
+
ret = sframe_read_header(sec);
if (ret) {
dbg_print_header(sec);
@@ -408,8 +413,8 @@ int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,

ret = mtree_insert_range(sframe_mt, sec->text_start, sec->text_end, sec, GFP_KERNEL);
if (ret) {
- dbg("mtree_insert_range failed: text=%lx-%lx\n",
- sec->text_start, sec->text_end);
+ dbg_sec("mtree_insert_range failed: text=%lx-%lx\n",
+ sec->text_start, sec->text_end);
goto err_free;
}

@@ -431,7 +436,7 @@ static int __sframe_remove_section(struct mm_struct *mm,
struct sframe_section *sec)
{
if (!mtree_erase(&mm->sframe_mt, sec->text_start)) {
- dbg("mtree_erase failed: text=%lx\n", sec->text_start);
+ dbg_sec("mtree_erase failed: text=%lx\n", sec->text_start);
return -EINVAL;
}

diff --git a/kernel/unwind/sframe_debug.h b/kernel/unwind/sframe_debug.h
index 055c8c8fae24..4d121cdbb760 100644
--- a/kernel/unwind/sframe_debug.h
+++ b/kernel/unwind/sframe_debug.h
@@ -10,26 +10,55 @@
#define dbg(fmt, ...) \
pr_debug("%s (%d): " fmt, current->comm, current->pid, ##__VA_ARGS__)

+#define dbg_sec(fmt, ...) \
+ dbg("%s: " fmt, sec->filename, ##__VA_ARGS__)
+
static __always_inline void dbg_print_header(struct sframe_section *sec)
{
unsigned long fdes_end;

fdes_end = sec->fdes_start + (sec->num_fdes * sizeof(struct sframe_fde));

- dbg("SEC: sframe:0x%lx-0x%lx text:0x%lx-0x%lx "
- "fdes:0x%lx-0x%lx fres:0x%lx-0x%lx "
- "ra_off:%d fp_off:%d\n",
- sec->sframe_start, sec->sframe_end, sec->text_start, sec->text_end,
- sec->fdes_start, fdes_end, sec->fres_start, sec->fres_end,
- sec->ra_off, sec->fp_off);
+ dbg_sec("SEC: sframe:0x%lx-0x%lx text:0x%lx-0x%lx "
+ "fdes:0x%lx-0x%lx fres:0x%lx-0x%lx "
+ "ra_off:%d fp_off:%d\n",
+ sec->sframe_start, sec->sframe_end, sec->text_start, sec->text_end,
+ sec->fdes_start, fdes_end, sec->fres_start, sec->fres_end,
+ sec->ra_off, sec->fp_off);
+}
+
+static inline void dbg_init(struct sframe_section *sec)
+{
+ struct mm_struct *mm = current->mm;
+ struct vm_area_struct *vma;
+
+ guard(mmap_read_lock)(mm);
+ vma = vma_lookup(mm, sec->sframe_start);
+ if (!vma)
+ sec->filename = kstrdup("(vma gone???)", GFP_KERNEL);
+ else if (vma->vm_file)
+ sec->filename = kstrdup_quotable_file(vma->vm_file, GFP_KERNEL);
+ else if (!vma->vm_mm)
+ sec->filename = kstrdup("(vdso)", GFP_KERNEL);
+ else
+ sec->filename = kstrdup("(anonymous)", GFP_KERNEL);
+}
+
+static inline void dbg_free(struct sframe_section *sec)
+{
+ kfree(sec->filename);
}

#else /* !CONFIG_DYNAMIC_DEBUG */

#define dbg(args...) no_printk(args)
+#define dbg_sec(args... ) no_printk(args)

static inline void dbg_print_header(struct sframe_section *sec) {}

+static inline void dbg_init(struct sframe_section *sec) {}
+static inline void dbg_free(struct sframe_section *sec) {}
+
#endif /* !CONFIG_DYNAMIC_DEBUG */

#endif /* _SFRAME_DEBUG_H */
--
2.48.1