fprintf: Print number of bit paddings in class member types

In addition to paddings (holes at the end of a struct), byte holes and
bit holes, inform about bit paddings in bitfields at the end of the
structs of non-pointer members.

For instance, see 'struct device' in the Linux kernel, mostly without
holes (just padding, 3 bytes and 3 bits) but with members with types
that have holes:

  $ pahole device
  struct device {
  	struct kobject             kobj;                 /*     0    64 */

  	/* XXX last struct has 27 bits of padding */

  	/* --- cacheline 1 boundary (64 bytes) --- */
  	struct device *            parent;               /*    64     8 */
  	struct device_private *    p;                    /*    72     8 */
  	const char  *              init_name;            /*    80     8 */
  	const struct device_type  * type;                /*    88     8 */
  	const struct bus_type  *   bus;                  /*    96     8 */
  	struct device_driver *     driver;               /*   104     8 */
  	void *                     platform_data;        /*   112     8 */
  	void *                     driver_data;          /*   120     8 */
  	/* --- cacheline 2 boundary (128 bytes) --- */
  	struct mutex               mutex;                /*   128    32 */
  	struct dev_links_info      links;                /*   160    56 */

  	/* XXX last struct has 4 bytes of padding */

  	/* --- cacheline 3 boundary (192 bytes) was 24 bytes ago --- */
  	struct dev_pm_info         power;                /*   216   312 */

  	/* XXX last struct has 2 holes, 3 bit holes */

  	/* --- cacheline 8 boundary (512 bytes) was 16 bytes ago --- */
  	struct dev_pm_domain *     pm_domain;            /*   528     8 */
  	struct em_perf_domain *    em_pd;                /*   536     8 */
  	struct dev_pin_info *      pins;                 /*   544     8 */
  	struct dev_msi_info        msi;                  /*   552    16 */
  	const struct dma_map_ops  * dma_ops;             /*   568     8 */
  	/* --- cacheline 9 boundary (576 bytes) --- */
  	u64 *                      dma_mask;             /*   576     8 */
  	u64                        coherent_dma_mask;    /*   584     8 */
  	u64                        bus_dma_limit;        /*   592     8 */
  	const struct bus_dma_region  * dma_range_map;    /*   600     8 */
  	struct device_dma_parameters * dma_parms;        /*   608     8 */
  	struct list_head           dma_pools;            /*   616    16 */
  	struct cma *               cma_area;             /*   632     8 */
  	/* --- cacheline 10 boundary (640 bytes) --- */
  	struct io_tlb_mem *        dma_io_tlb_mem;       /*   640     8 */
  	struct dev_archdata        archdata;             /*   648     0 */
  	struct device_node *       of_node;              /*   648     8 */
  	struct fwnode_handle *     fwnode;               /*   656     8 */
  	int                        numa_node;            /*   664     4 */
  	dev_t                      devt;                 /*   668     4 */
  	u32                        id;                   /*   672     4 */
  	spinlock_t                 devres_lock;          /*   676     4 */
  	struct list_head           devres_head;          /*   680    16 */
  	const struct class  *      class;                /*   696     8 */
  	/* --- cacheline 11 boundary (704 bytes) --- */
  	const struct attribute_group  * * groups;        /*   704     8 */
  	void                       (*release)(struct device *); /*   712     8 */
  	struct iommu_group *       iommu_group;          /*   720     8 */
  	struct dev_iommu *         iommu;                /*   728     8 */
  	struct device_physical_location * physical_location; /*   736     8 */
  	enum device_removable      removable;            /*   744     4 */
  	bool                       offline_disabled:1;   /*   748: 0  1 */
  	bool                       offline:1;            /*   748: 1  1 */
  	bool                       of_node_reused:1;     /*   748: 2  1 */
  	bool                       state_synced:1;       /*   748: 3  1 */
  	bool                       can_match:1;          /*   748: 4  1 */

  	/* size: 752, cachelines: 12, members: 45 */
  	/* padding: 3 */
  	/* member types with holes: 1, total: 2, bit holes: 1, total: 3, bit paddings: 1, total: 27 bits */
  	/* paddings: 1, sum paddings: 4 */
  	/* bit_padding: 3 bits */
  	/* last cacheline: 48 bytes */
  };

  $

Now look at the first member bit padding:

  $ pahole kobject
  struct kobject {
  	const char  *              name;                       /*     0     8 */
  	struct list_head           entry;                      /*     8    16 */
  	struct kobject *           parent;                     /*    24     8 */
  	struct kset *              kset;                       /*    32     8 */
  	const struct kobj_type  *  ktype;                      /*    40     8 */
  	struct kernfs_node *       sd;                         /*    48     8 */
  	struct kref                kref;                       /*    56     4 */
  	unsigned int               state_initialized:1;        /*    60: 0  4 */
  	unsigned int               state_in_sysfs:1;           /*    60: 1  4 */
  	unsigned int               state_add_uevent_sent:1;    /*    60: 2  4 */
  	unsigned int               state_remove_uevent_sent:1; /*    60: 3  4 */
  	unsigned int               uevent_suppress:1;          /*    60: 4  4 */

  	/* size: 64, cachelines: 1, members: 12 */
  	/* bit_padding: 27 bits */
  };

  $

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 23 insertions, 3 deletions

diff --git a/dwarves_fprintf.c b/dwarves_fprintf.c
index 2fa489a4..9e5e6631 100644
--- a/dwarves_fprintf.c
+++ b/dwarves_fprintf.c
@@ -1464,11 +1464,13 @@ out:
 
 struct member_types_holes {
 	uint16_t nr_paddings;
+	uint16_t nr_with_bit_paddings;
 	uint16_t nr_with_holes;
 	uint16_t nr_with_bit_holes;
 	uint16_t total_nr_holes;
 	uint16_t total_nr_bit_holes;
 	uint32_t sum_paddings;
+	uint32_t sum_bit_paddings;
 };
 
 static size_t class__fprintf_member_type_holes(struct class *class, const struct cu *cu,
@@ -1477,7 +1479,7 @@ static size_t class__fprintf_member_type_holes(struct class *class, const struct
 {
 	size_t printed = 0;
 	uint16_t padding;
-	uint8_t nr_holes, nr_bit_holes;
+	uint8_t nr_holes, nr_bit_holes, bit_padding;
 	bool first = true;
 	/*
 	 * We may not yet have looked for holes and paddings in this member's
@@ -1487,10 +1489,11 @@ static size_t class__fprintf_member_type_holes(struct class *class, const struct
 	class__infer_packed_attributes(class, cu);
 
 	padding = class->padding;
+	bit_padding = class->bit_padding;
 	nr_holes = class->nr_holes;
 	nr_bit_holes = class->nr_bit_holes;
 
-	if (!padding && !nr_holes && !nr_bit_holes)
+	if (!padding && !bit_padding && !nr_holes && !nr_bit_holes)
 		return 0;
 
 	if (!(*newline)++) {
@@ -1508,6 +1511,14 @@ static size_t class__fprintf_member_type_holes(struct class *class, const struct
 		first = false;
 	}
 
+	if (bit_padding) {
+		++holes->nr_with_bit_paddings;
+		holes->sum_bit_paddings += bit_padding;
+
+		printed += fprintf(fp, "%s %d bit%s of padding", first ? "" : ",",  bit_padding, bit_padding != 1 ? "s" : "");
+		first = false;
+	}
+
 	if (nr_holes) {
 		++holes->nr_with_holes;
 		holes->total_nr_holes += nr_holes;
@@ -1885,7 +1896,9 @@ static size_t __class__fprintf(struct class *class, const struct cu *cu,
 				   cconf.indent,
 				   tabs, class->padding);
 
-	if (member_types_holes.nr_with_holes > 0 || member_types_holes.nr_with_bit_holes > 0) {
+	if (member_types_holes.nr_with_holes > 0 ||
+	    member_types_holes.nr_with_bit_holes > 0 ||
+	    member_types_holes.nr_with_bit_paddings > 0) {
 		bool first = true;
 
 		printed += fprintf(fp, "%.*s/* member types with ", cconf.indent, tabs);
@@ -1897,6 +1910,13 @@ static size_t __class__fprintf(struct class *class, const struct cu *cu,
 		if (member_types_holes.nr_with_bit_holes > 0) {
 			printed += fprintf(fp, "%sbit holes: %u, total: %u", first ? "" : ", ",
 					   member_types_holes.nr_with_bit_holes, member_types_holes.total_nr_bit_holes);
+			first = false;
+		}
+		if (member_types_holes.nr_with_bit_paddings > 0) {
+			printed += fprintf(fp, "%sbit paddings: %u, total: %u bit%s", first ? "" : ", ",
+					   member_types_holes.nr_with_bit_paddings,
+					   member_types_holes.sum_bit_paddings,
+					   member_types_holes.sum_bit_paddings > 1 ? "s" : "");
 		}
 		printed += fprintf(fp, " */\n");
 	}