tools/slabratetop: call to undeclared function 'slab_address'

[Rtoax]

When my system uses SLUB And the kernel version >=5.16, there are the following problems:

$ sudo ./slabratetop.py
In file included from /virtual/main.c:13:
include/linux/slub_def.h:162:26: warning: call to undeclared function 'slab_address'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
        void *object = x - (x - slab_address(slab)) % cache->size;
                                ^
include/linux/slub_def.h:162:46: error: invalid operands to binary expression ('void *' and 'unsigned int')
        void *object = x - (x - slab_address(slab)) % cache->size;
                           ~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~
include/linux/slub_def.h:164:8: error: incomplete definition of type 'struct slab'
                (slab->objects - 1) * cache->size;
                 ~~~~^
include/linux/kasan.h:13:8: note: forward declaration of 'struct slab'
struct slab;
       ^
In file included from /virtual/main.c:13:
include/linux/slub_def.h:184:31: warning: call to undeclared function 'slab_address'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
        return __obj_to_index(cache, slab_address(slab), obj);
                                     ^
include/linux/slub_def.h:184:31: error: incompatible integer to pointer conversion passing 'int' to parameter of type 'void *' [-Wint-conversion]
        return __obj_to_index(cache, slab_address(slab), obj);
                                     ^~~~~~~~~~~~~~~~~~
include/linux/slub_def.h:173:14: note: passing argument to parameter 'addr' here
                                          void *addr, void *obj)
                                                ^
include/linux/slub_def.h:190:13: error: incomplete definition of type 'struct slab'
        return slab->objects;
               ~~~~^
include/linux/kasan.h:13:8: note: forward declaration of 'struct slab'
struct slab;
       ^
2 warnings and 4 errors generated.
Traceback (most recent call last):
  File "/home/rongtao/Git/bcc/tools/./slabratetop.py", line 111, in <module>
    b = BPF(text=bpf_text)
        ^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/bcc/__init__.py", line 475, in __init__
    raise Exception("Failed to compile BPF module %s" % (src_file or "<text>"))
Exception: Failed to compile BPF module <text>

see commit 40f3bf0cb04c("mm: Convert struct page to struct slab in functions used by other subsystems")

This issue should be modified in the kernel, I'm trying to fix this, kernel submit mm: Functions used internally should not be put into slub_def.h totally solve this fatal error, hope it'll be merged to kernel souce code tree.

[Rtoax]

kernel submit: https://lore.kernel.org/all/tencent_ABA832E296819D1053D6C625ADCAF76BC706@qq.com/

[Rtoax]

Sadly, kernel maintainer tends to not merge the above commit mm: Functions used internally should not be put into slub_def.h, that is to say, slabratetop.py could not include <sl*b_def.h> anymore since kernel commit 40f3bf0cb04c(“mm: Convert struct page to struct slab in functions used by other subsystems”). may we should solve the kmem_cache structure with BTF way.

[yonghong-song]

As a temporary workaround, something like below will work,

diff --git a/tools/slabratetop.py b/tools/slabratetop.py
index ac44b2bd..084875f3 100755
--- a/tools/slabratetop.py
+++ b/tools/slabratetop.py
@@ -65,6 +65,78 @@ bpf_text = """
 // 5.9, but it does not hurt to have it here for versions 5.4 to 5.8.
 struct memcg_cache_params {};
 
+struct slab {
+        unsigned long __page_flags;
+
+#if defined(CONFIG_SLAB)
+
+        struct kmem_cache *slab_cache;
+        union {
+                struct {
+                        struct list_head slab_list;
+                        void *freelist; /* array of free object indexes */
+                        void *s_mem;    /* first object */
+                };
+                struct rcu_head rcu_head;
+        };
+        unsigned int active;
+
+#elif defined(CONFIG_SLUB)
+
+        struct kmem_cache *slab_cache;
+        union {
+                struct {
+                        union {
+                                struct list_head slab_list;
+#ifdef CONFIG_SLUB_CPU_PARTIAL
+                                struct {
+                                        struct slab *next;
+                                        int slabs;      /* Nr of slabs left */
+                                };
+#endif
+                        };
+                        /* Double-word boundary */
+                        void *freelist;         /* first free object */
+                        union {
+                                unsigned long counters;
+                                struct {
+                                        unsigned inuse:16;
+                                        unsigned objects:15;
+                                        unsigned frozen:1;
+                                };
+                        };
+                };
+                struct rcu_head rcu_head;
+        };
+        unsigned int __unused;
+
+#elif defined(CONFIG_SLOB)
+
+        struct list_head slab_list;
+        void *__unused_1;
+        void *freelist;         /* first free block */
+        long units;
+        unsigned int __unused_2;
+
+#else
+#error "Unexpected slab allocator configured"
+#endif
+
+        atomic_t __page_refcount;
+#ifdef CONFIG_MEMCG
+        unsigned long memcg_data;
+#endif
+};
+
+#define slab_folio(s)           (_Generic((s),                          \
+        const struct slab *:    (const struct folio *)s,                \
+        struct slab *:          (struct folio *)s))
+
+static inline void *slab_address(const struct slab *slab)
+{
+        return folio_address(slab_folio(slab));
+}
+
 #ifdef CONFIG_SLUB
 #include <linux/slub_def.h>
 #else

The above is based on latest bpf-next code base and need to be guarded with proper kernel versions or by some btf struct change around 40f3bf0cb04c("mm: Convert struct page to struct slab in functions used by other subsystems"). Need to double check the structure definition for earlier versions as well.

Currently, there is an effort (#4405) to move bcc source to be more libbpf-processible. Hopefully with that it can make it easier to access the structure easier.

[Rtoax]

@yonghong-song Thanks, Song. This patch solved my problem as a temporary solution. I have followed the submission of 4405, thanks again.

[yonghong-song]

@Rtoax Although this is a temporary workaround, could you still add the above temporary solution to slabratetop tool? This way, we can at least make slabratetop work for the >= 5.16 kernels.

[Rtoax]

@yonghong-song Hi, Song, I just submit a PR #4447