Breakpoint 1 at 0xc0016b18: file kernel/panic.c, line 74.
(gdb) b sys_sync
Breakpoint 2 at 0xc005a8c8: file fs/buffer.c, line 296.
(gdb) b yosemite_setup_arch
Breakpoint 3 at 0xc020f438: file arch/ppc/platforms/4xx/yosemite.c, line 116.
(gdb) c
Continuing.
Breakpoint 3, yosemite_setup_arch ()
at arch/ppc/platforms/4xx/yosemite.c:116
116 def = ocp_get_one_device(OCP_VENDOR_IBM, OCP_FUNC_EMAC, 0);
(gdb) l
111 struct ocp_def *def;
112 struct ocp_func_emac_data *emacdata;
113
114 /* Set mac_addr and phy mode for each EMAC */
115
116 def = ocp_get_one_device(OCP_VENDOR_IBM, OCP_FUNC_EMAC, 0);
117 emacdata = def->additions;
118 memcpy(emacdata->mac_addr, __res.bi_enetaddr, 6);
119 emacdata->phy_mode = PHY_MODE_RMII;
120
(gdb) p yosemite_setup_arch
$1 = {void (void)} 0xc020f41c <yosemite_setup_arch>
Referring back to Listing 14-4, notice that the function yosemite_setup_arch() actually falls on line 306 of the file yosemite.c. Compare that with Listing 14-7. We hit the breakpoint, but gdb reports the breakpoint at file yosemite.c line 116. It appears at first glance to be a mismatch of line numbers between the debugger and the corresponding source code. Is this a gdb bug? First let's confirm what the compiler produced for debug information. Using the readelf[93] tool described in Chapter 13, 'Development Tools,' we can examine the debug information for this function produced by the compiler.
$ ppc_44x-readelf --debug-dump=info vmlinux | grep - u6 yosemite_setup_arch | tail -n 7
DW_AT_name : (indirect string, offset: 0x9c04): yosemite_setup_arch
DW_AT_decl_file : 1
DW_AT_decl_line : 307
DW_AT_prototyped : 1
DW_AT_low_pc : 0xc020f41c
DW_AT_high_pc : 0xc020f794
DW_AT_frame_base : 1 byte block: 51 (DW_OP_reg1)
We don't have to be experts at reading DWARF2 debug records[94] to recognize that the function in question is reported at line 307 in our source file. We can confirm this using the addr2line utility, also introduced in Chapter 13. Using the address derived from gdb in Listing 14-7:
$ ppc_44x-addr2line -e vmlinux 0xc020f41c
arch/ppc/platforms/4xx/yosemite.c:307
At this point, gdb is reporting our breakpoint at line 116 of the yosemite.c file. To understand what is happening, we need to look at the assembler output of the function as reported by gdb. Listing 14-8 is the output from gdb after issuing the disassemble command on the yosemite_setup_arch() function.
Listing 14-8. Disassemble Function yosemite_setup_arch
(gdb) disassemble yosemite_setup_arch
0xc020f41c <yosemite_setup_arch+0>: mflr r0
0xc020f420 <yosemite_setup_arch+4>: stwu r1,-48(r1)
0xc020f424 <yosemite_setup_arch+8>: li r4,512
0xc020f428 <yosemite_setup_arch+12>: li r5,0
0xc020f42c <yosemite_setup_arch+16>: li r3,4116
0xc020f430 <yosemite_setup_arch+20>: stmw r25,20(r1)
0xc020f434 <yosemite_setup_arch+24>: stw r0,52(r1)
0xc020f438 <yosemite_setup_arch+28>: bl 0xc000d344
<ocp_get_one_device>
0xc020f43c <yosemite_setup_arch+32>: lwz r31,32(r3)
0xc020f440 <yosemite_setup_arch+36>: lis r4,-16350
0xc020f444 <yosemite_setup_arch+40>: li r28,2
0xc020f448 <yosemite_setup_arch+44>: addi r4,r4,21460
0xc020f44c <yosemite_setup_arch+48>: li r5,6
0xc020f450 <yosemite_setup_arch+52>: lis r29,-16350
0xc020f454 <yosemite_setup_arch+56>: addi r3,r31,48
0xc020f458 <yosemite_setup_arch+60>: lis r25,-16350
0xc020f45c <yosemite_setup_arch+64>: bl 0xc000c708
<memcpy>
0xc020f460 <yosemite_setup_arch+68>: stw r28,44(r31)
0xc020f464 <yosemite_setup_arch+72>: li r4,512
0xc020f468 <yosemite_setup_arch+76>: li r5,1
0xc020f46c <yosemite_setup_arch+80>: li r3,4116
0xc020f470 <yosemite_setup_arch+84>: addi r26,r25,15104
0xc020f474 <yosemite_setup_arch+88>: bl 0xc000d344
<ocp_get_one_device>
0xc020f478 <yosemite_setup_arch+92>: lis r4,-16350
0xc020f47c <yosemite_setup_arch+96>: lwz r31,32(r3)
0xc020f480 <yosemite_setup_arch+100>: addi r4,r4,21534
0xc020f484 <yosemite_setup_arch+104>: li r5,6
0xc020f488 <yosemite_setup_arch+108>: addi r3,r31,48
0xc020f48c <yosemite_setup_arch+112>: bl 0xc000c708
<memcpy>
0xc020f490 <yosemite_setup_arch+116>: lis r4,1017
0xc020f494 <yosemite_setup_arch+120>: lis r5,168
0xc020f498 <yosemite_setup_arch+124>: stw r28,44(r31)
0xc020f49c <yosemite_setup_arch+128>: ori r4,r4,16554
0xc020f4a0 <yosemite_setup_arch+132>: ori r5,r5,49152
0xc020f4a4 <yosemite_setup_arch+136>: addi r3,r29,-15380
0xc020f4a8 <yosemite_setup_arch+140>: addi r29,r29,-15380
0xc020f4ac <yosemite_setup_arch+144>: bl 0xc020e338
<ibm440gx_get_clocks>
0xc020f4b0 <yosemite_setup_arch+148>: li r0,0
0xc020f4b4 <yosemite_setup_arch+152>: lis r11,-16352
0xc020f4b8 <yosemite_setup_arch+156>: ori r0,r0,50000
