KGDB不将地址与符号相关联

Question

我正在调试Linux内核，特别是蓝牙内核模块。我想逐步了解net/bluetooth/l2cap_core.c中的代码

• 主机:LinuxMint18.3(运行在VM中)。
• 目标机器:覆盆子pi 3b+

我使用交叉编译工具在主机上使用调试符号编译内核.在pi上加载内核，它可以很好地引导，我可以在/proc/kallsyms中看到我的目标符号/proc/kallsyms。

# grep l2cap_parse_conf_rsp /proc/kallsyms
bf2b67c4 t l2cap_parse_conf_rsp [bluetooth]

我在KDB中设置了断点。

kdb> bp l2cap_parse_conf_rsp
Instruction(i) BP #0 at 0xbf2a77c4 ([bluetooth]l2cap_parse_conf_rsp)
    is enabled  addr at 00000000bf2a77c4, hardtype=0 installed=0
kdb> go

我发送一个蓝牙数据包，并导致断点触发。一旦我们进入KDB，我就切换到KGDB模式。

#
Entering kdb (current=0xda4aa8e0, pid 201) due to Breakpoint @ 0xbf2a77c4
kdb>kgdb
Entering please attach debugger or use $D#44+ or $3#33

在编译内核的主机上，我运行gdb-multiarch ./vmlinux。我使用lx-symbols加载符号地址。这些符号似乎已正确加载：

(gdb) info symbol l2cap_parse_conf_rsp
__UNIQUE_ID_alias38 + 43 in section .modinfo of /home/alex/pi/linux/drivers/bluetooth/btusb.ko
__this_module + 172 in section .gnu.linkonce.this_module of /home/alex/pi/linux/drivers/net/wireless/broadcom/brcm80211/brcmutil/brcmutil.ko
l2cap_parse_conf_rsp in section .text.unlikely of /home/alex/pi/linux/net/bluetooth/bluetooth.ko
__UNIQUE_ID_maximum_substreams19 + 14 in section .modinfo of /home/alex/pi/linux/sound/core/snd-pcm.ko
trace_event_define_fields_cfg80211_ready_on_channel + 204 in section .init.text of /home/alex/pi/linux/net/wireless/cfg80211.ko
__ksymtab_snd_unregister_oss_device + 4 in section __ksymtab of /home/alex/pi/linux/sound/core/snd.ko
__UNIQUE_ID_vermagic8 + 46 in section .modinfo of /home/alex/pi/linux/net/rfkill/rfkill.ko
____versions + 588 in section __versions of /home/alex/pi/linux/drivers/char/broadcom/bcm2835-gpiomem.ko
____versions + 724 in section __versions of /home/alex/pi/linux/drivers/regulator/fixed.ko
____versions + 560 in section __versions of /home/alex/pi/linux/drivers/uio/uio_pdrv_genirq.ko
ipv6_addr_label_rtnl_register + 76 in section .init.text of /home/alex/pi/linux/net/ipv6/ipv6.ko
(gdb)

我甚至可以看到源代码：

(gdb) list l2cap_parse_conf_rsp
3516            return ptr - data;
3517    }
3518
3519    static int l2cap_parse_conf_rsp(struct l2cap_chan *chan, void *rsp, int len,
3520                                    void *data, u16 *result)
3521    {
3522            struct l2cap_conf_req *req = data;
3523            void *ptr = req->data;
3524            int type, olen;
3525            unsigned long val;

但是，gdb在我逐步遍历代码时无法获取该信息。例如，当我打印回溯跟踪时，当前函数显示为??

(gdb) bt
#0  0xbf2ae7c4 in ?? ()
#1  0xbf299a14 in l2cap_config_rsp (data=<optimized out>, cmd_len=<optimized out>, cmd=<optimized out>, conn=<optimized out>)
    at net/bluetooth/l2cap_core.c:4176
#2  0xbf29ad90 in l2cap_recv_acldata (hcon=<optimized out>, skb=0xd856a240, flags=<optimized out>) at net/bluetooth/l2cap_core.c:7567
#3  0xbf26f9cc in hci_acldata_packet (skb=<optimized out>, hdev=<optimized out>) at net/bluetooth/hci_core.c:4018
#4  hci_rx_work (work=0xda4b5760) at net/bluetooth/hci_core.c:4194
#5  0xc0037f54 in process_one_work (worker=0xd7c10c00, work=0xda4b5760) at kernel/workqueue.c:2096
#6  0xc0038344 in worker_thread (__worker=0xda5d2ae0) at kernel/workqueue.c:2230
#7  0xc003dcc4 in kthread (_create=0xd8995340) at kernel/kthread.c:211
#8  0xc000fba8 in ret_from_fork () at arch/arm/kernel/entry-common.S:118
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

我遗漏了什么？如何告诉GDB地址0xbf2ae7c4对应于符号l2cap_parse_conf_rsp

Answer 1

我会把这个标记为封闭的。原来，我正在寻找的特定符号位于".text.unlikely“部分，而lx-符号在该部分中不查找符号。我在scripts/gdb/linux/symbols.py中编辑了lx符号脚本，以包括.text.unlikely：

for section_name in [".data", ".data..read_mostly", ".rodata", ".bss", ".text.unlikely"]: