[PATCH 5/5] pahole: Introduce --with_embedded_flexible_array

[Arnaldo Carvalho de Melo <acme@kernel.org>]

From: Arnaldo Carvalho de Melo <acme@redhat.com>

To print structs that have as one of its members a struct with a
flexible array, i.e. the outer script has a flexible array in its
middle, which is dangerous.

One example should illustrate this nicely:

  ⬢[acme@toolbox pahole]$ pahole --with_embedded_flexible_array --sizes | wc -l
  103
  ⬢[acme@toolbox pahole]$ pahole --with_embedded_flexible_array --sizes | tail
  acpi_nhlt_format_config	44	0
  xts_request_ctx	168	0
  dbc_port	512	1
  ethtool_link_usettings	96	0
  pci_setup_rom	64	1
  lirc_fh	112	1
  lrw_request_ctx	96	0
  xt_standard_target	40	0
  xt_error_target	64	0
  bpf_ctx_convert	7280	0
  ⬢[acme@toolbox pahole]$ pahole lirc_fh
  struct lirc_fh {
  	struct list_head           list;                 /*     0    16 */
  	struct rc_dev *            rc;                   /*    16     8 */
  	int                        carrier_low;          /*    24     4 */

  	/* XXX 4 bytes hole, try to pack */

  	struct {
  		union {
  			struct __kfifo kfifo;            /*    32    24 */
  			unsigned int * type;             /*    32     8 */
  			const unsigned int  * const_type; /*    32     8 */
  			char *     rectype;              /*    32     8 */
  			unsigned int * ptr;              /*    32     8 */
  			const unsigned int  * ptr_const; /*    32     8 */
  		};                                       /*    32    24 */
  		unsigned int       buf[];                /*    56     0 */
  	} rawir;                                         /*    32    24 */
  	struct {
  		union {
  			struct __kfifo kfifo;            /*    56    24 */
  			struct lirc_scancode * type;     /*    56     8 */
  			const struct lirc_scancode  * const_type; /*    56     8 */
  			char *     rectype;              /*    56     8 */
  			struct lirc_scancode * ptr;      /*    56     8 */
  			const struct lirc_scancode  * ptr_const; /*    56     8 */
  		};                                       /*    56    24 */
  		/* --- cacheline 1 boundary (64 bytes) was 16 bytes ago --- */
  		struct lirc_scancode buf[];              /*    80     0 */
  	} scancodes;                                     /*    56    24 */
  	wait_queue_head_t          wait_poll;            /*    80    24 */
  	u8                         send_mode;            /*   104     1 */
  	u8                         rec_mode;             /*   105     1 */

  	/* size: 112, cachelines: 2, members: 8 */
  	/* sum members: 102, holes: 1, sum holes: 4 */
  	/* padding: 6 */
  	/* last cacheline: 48 bytes */
  };

  ⬢[acme@toolbox pahole]$

Another case:

  ⬢[acme@toolbox pahole]$ pahole -E ethtool_link_usettings
  struct ethtool_link_usettings {
  	struct ethtool_link_settings {
  		/* typedef __u32 */ unsigned int       cmd;                              /*     0     4 */
  		/* typedef __u32 */ unsigned int       speed;                            /*     4     4 */
  		/* typedef __u8 */ unsigned char      duplex;                            /*     8     1 */
  		/* typedef __u8 */ unsigned char      port;                              /*     9     1 */
  		/* typedef __u8 */ unsigned char      phy_address;                       /*    10     1 */
  		/* typedef __u8 */ unsigned char      autoneg;                           /*    11     1 */
  		/* typedef __u8 */ unsigned char      mdio_support;                      /*    12     1 */
  		/* typedef __u8 */ unsigned char      eth_tp_mdix;                       /*    13     1 */
  		/* typedef __u8 */ unsigned char      eth_tp_mdix_ctrl;                  /*    14     1 */
  		/* typedef __s8 */ signed char        link_mode_masks_nwords;            /*    15     1 */
  		/* typedef __u8 */ unsigned char      transceiver;                       /*    16     1 */
  		/* typedef __u8 */ unsigned char      master_slave_cfg;                  /*    17     1 */
  		/* typedef __u8 */ unsigned char      master_slave_state;                /*    18     1 */
  		/* typedef __u8 */ unsigned char      rate_matching;                     /*    19     1 */
  		/* typedef __u32 */ unsigned int       reserved[7];                      /*    20    28 */
  		/* typedef __u32 */ unsigned int       link_mode_masks[];                /*    48     0 */
  	} base; /*     0    48 */
  	struct {
  		/* typedef __u32 */ unsigned int       supported[4];                     /*    48    16 */
  		/* --- cacheline 1 boundary (64 bytes) --- */
  		/* typedef __u32 */ unsigned int       advertising[4];                   /*    64    16 */
  		/* typedef __u32 */ unsigned int       lp_advertising[4];                /*    80    16 */
  	} link_modes;                                                                    /*    48    48 */

  	/* size: 96, cachelines: 2, members: 2 */
  	/* last cacheline: 32 bytes */
  };

  ⬢[acme@toolbox pahole]$

Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 man-pages/pahole.1 |  4 ++++
 pahole.c           | 13 +++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
index 7c1a69ad23690c75..19dfe676c9e30509 100644
--- a/man-pages/pahole.1
+++ b/man-pages/pahole.1
@@ -397,6 +397,10 @@ for instance when using the \fB\-\-reorganize\fR option.
 .B \-P, \-\-with_flexible_array
 Show only structs that have a flexible array.
 
+.TP
+.B \-P, \-\-with_embedded_flexible_array
+Show only structs that have an embedded flexible array, i.e. a contained struct that has flexible arrays, a flexible array "in the middle".
+
 .TP
 .B \-q, \-\-quiet
 Be quieter.
diff --git a/pahole.c b/pahole.c
index 8bdfaf3e84c407d7..b9e97ef15e6c732e 100644
--- a/pahole.c
+++ b/pahole.c
@@ -66,6 +66,7 @@ static uint16_t nr_bit_holes;
 static uint16_t hole_size_ge;
 static uint8_t show_packable;
 static bool show_with_flexible_array;
+static bool show_with_embedded_flexible_array;
 static uint8_t global_verbose;
 static uint8_t recursive;
 static size_t cacheline_size;
@@ -825,6 +826,9 @@ static struct class *class__filter(struct class *class, struct cu *cu,
 	if (show_with_flexible_array && !class__has_flexible_array(class, cu))
 		return NULL;
 
+	if (show_with_embedded_flexible_array && !class__has_embedded_flexible_array(class, cu))
+		return NULL;
+
 	return class;
 }
 
@@ -1226,6 +1230,7 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
 #define ARGP_running_kernel_vmlinux 346
 #define ARG_padding_ge		   347
 #define ARG_padding		   348
+#define ARGP_with_embedded_flexible_array 349
 
 /* --btf_features=feature1[,feature2,..] allows us to specify
  * a list of requested BTF features or "default" to enable all default
@@ -1505,6 +1510,11 @@ static const struct argp_option pahole__options[] = {
 		.key  = ARGP_with_flexible_array,
 		.doc  = "show only structs with a flexible array",
 	},
+	{
+		.name = "with_embedded_flexible_array",
+		.key  = ARGP_with_embedded_flexible_array,
+		.doc  = "show only structs with an embedded flexible array (contaning a struct that has a flexible array)",
+	},
 	{
 		.name = "expand_types",
 		.key  = 'E',
@@ -2006,6 +2016,9 @@ static error_t pahole__options_parser(int key, char *arg,
 		parse_btf_features("all", false);	break;
 	case ARGP_with_flexible_array:
 		show_with_flexible_array = true;	break;
+	case ARGP_with_embedded_flexible_array:
+		just_structs = true;
+		show_with_embedded_flexible_array = true; break;
 	case ARGP_prettify_input_filename:
 		prettify_input_filename = arg;		break;
 	case ARGP_sort_output:
-- 
2.46.2