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Kernel Extensions and Device Support Programming Concepts

Maps and Listings as Tools for the LLDB Kernel Debug Program

The assembler listing and the map files are essential tools for debugging using the LLDB Kernel Debugger. In order to create the assembler list file during compilation, use the -qlist option while compiling. Also use the -qsource option to get the C source listing in the same file:

cc -c -DEBUG -D_KERNEL -DIBMR2 demodd.c -qsource -qlist

In order to obtain the map file, use the -bmap:FileName option on the link editor, enter:

ld -o demodd demodd.o -edemoconfig -bimport:/lib/kernex.exp \
-lsys  -lcsys -bmap:demodd.map -bE:demodd.exp

You can also create a map file with a slightly different format by using the nm command. For example, use the following command to get a map listing for the kernel (/unix):

nm -xv /unix > unix.m

Compiler Listing

The assembler and source listing is used to correlate any C source line with the corresponding assembler lines. The following is a portion of the C source code for a sample device driver. The left column is the line number in the source code:

.
.
185
186    if (result = devswadd(devno, &demo_dsw)){
187         printf("democonfig : failed to add entry points\n");
188         (void)devswdel(devno);
189         break;
190    }
191    dp->inited = 1;
192    demos_inited++;
193    printf("democonfig : CFG_INIT success\n");
194    break;
195
.
.

The following is a portion of the assembler listing for the corresponding C code shown previously. The left column is the C source line for the corresponding assembler statement. Each C source line can have multiple assembler source lines. The second column is the offset of the assembler instruction with respect to the kernel extension entry point.

.
.
186| 000218 l     80610098  2  L4Z   gr3=devno(gr1,152)
186| 00021C cal   389F0000  1  LR    gr4=gr31
186| 000220 bl    4BFFFDE1  0  CALL  gr3=devswadd,2,
gr3,(struct_4198576)",gr4,devswadd",gr1,cr[01567],gr0",
gr4"-gr12",fp0"-fp13"
186| 000224 cror  4DEF7B82  1
186| 000228 st    9061005C  2  ST4A  #2357(gr1,92)=gr3
186| 00022C st    9061003C  1  ST4A  result(gr1,60)=gr3
186| 000230 l     8061005C  1  L4A   gr3=#2357(gr1,92)
186| 000234 cmpi  2C830000  2  C4    cr1=gr3,0
186| 000238 bc    41860020  3  BT    CL.16,cr1,0x4/eq
187| 00023C ai    307F01A4  1  AI    gr3=gr31,420
187| 000240 bl    4BFFFDC1  2  CALL  gr3=printf,1,'democonfig :
failed to add entry points",gr3,printf",gr1,cr[01567],gr0",
gr4"-gr12",fp0"-fp13"
187| 000244 cror  4DEF7B82  1
188| 000248 l     80610098  2  L4Z   gr3=devno(gr1,152)
188| 00024C bl    4BFFFDB5  0  CALL  gr3=devswdel,1,gr3,
devswdel",gr1,cr[01567],gr0",gr4"-gr12",fp0"-fp13"
188| 000250 cror  4DEF7B82  1
189| 000254 b     48000104  0  B     CL.6
186|                           CL.16:
191| 000258 l     80810040  2  L4Z   gr4=dp(gr1,64)
191| 00025C cal   38600001  1  LI    gr3=1
191| 000260 stb   98640004  1  ST1Z  (char)(gr4,4)=gr3
192| 000264 l     8082000C  1  L4A   gr4=.demos_inited(gr2,0)
192| 000268 l     80640000  2  L4A   gr3=demos_inited(gr4,0)
192| 00026C ai    30630001  2  AI    gr3=gr3,1
192| 000270 st    90640000  1  ST4A  demos_inited(gr4,0)=gr3
193| 000274 ai    307F01D0  1  AI    gr3=gr31,464
193| 000278 bl    4BFFFD89  0  CALL  gr3=printf,1,'democonfig :
CFG_INIT success",gr3,printf",gr1,cr[01567],gr0",gr4"-gr12",
fp0"-fp13"
193| 00027C cror  4DEF7B82  1
194| 000280 b     480000D8  0  B     CL.6
.
.

Now with both the assembler listing and the C source listing, you can determine the assembler instruction for a C statement. As an example, consider the C source line at line 191 in the sample code:

191	dp->inited = 1;

The corresponding assembler instructions are:

191| 000258 l     80810040  2  L4Z   gr4=dp(gr1,64)
191| 00025C cal   38600001  1  LI    gr3=1
191| 000260 stb   98640004  1  ST1Z  (char)(gr4,4)=gr3

The offsets of these instructions within the sample device driver (demodd) are 000258, 00025C, and 000260.

Map File

The binder map file is a symbol map in address order format. Each symbol listed in the map file has a storage class (CL) and a type (TY) associated with it.

Storage classes correspond to the XMC_XX variables defined in the syms.h file. Each storage class belongs to one of the following section types:

.text Contains read-only data (instructions). Addresses listed in this section use the beginning of the .text section as origin. The .text section can contain one of the following storage class (CL) values:
DB Debug Table. Identifies a class of sections that has the same characteristics as read only data.
GL Glue Code. Identifies a section that has the same characteristics as a program code. This type of section has code to interface with a routine in another module. Part of the interface code requirement is to maintain TOC addressability across the call.
PR Program Code. Identifies the sections that provide executable instructions for the module.
R0 Read Only Data. Identifies the sections that contain constants that are not modified during execution.
TB Reserved.
TI Reserved.
XO Extended Op. Identifies a section of code that is to be treated as a pseudo-machine instruction.
.data Contains read-write initialized data. Addresses listed in this section use the beginning of the .data section as origin. The .data section can contain one of the following storage class (CL) values:
DS Descriptor. Identifies a function descriptor. This information is used to describe function pointers in languages such as C and Fortran.
RW Read Write Data. Identifies a section that contains data that is known to require change during execution.
SV SVC. Identifies a section of code that is to be treated as a supervisory call.
T0 TOC Anchor. Used only by the predefined TOC symbol. Identifies the special symbol TOC. Used only by the TOC header.
TC TOC Entry. Identifies address data that will reside in the TOC.
TD TOC Data Entry. Identifies data that will reside in the TOC.
UA Unclassified. Identifies data that contains data of an unknown storage class.
.bss Contains read-write uninitialized data. Addresses listed in this section use the beginning of the .data section as origin. The .bss section contain one of the following storage class (CL) values:
BS BSS class. Identifies a section that contains uninitialized data.
UC Unnamed Fortran Common. Identifies a section that contains read write data.

Types correspond to the XTY_XX variables defined in the syms.h file. The type (TY) can be one of the following values:

ER External Reference
LD Label Definition
SD Section Definition
CM BSS Common Definition

The following is a map file for a sample device driver:

1  ADDRESS MAP FOR demodd
2                                               SOURCE-FILE(OBJECT) or
   *IE ADDRESS  LENGTH AL CL TY Sym# NAME       IMPORT-FILE{SHARED-OBJECT}
3  --- -------- ------ -- -- -- ---- ---------- --------------------------
4   I                        ER S1   pinned_heap  /lib/kernex.exp{/unix}
5   I                        ER S2   devswadd     /lib/kernex.exp{/unix}
6   I                        ER S3   devswdel     /lib/kernex.exp{/unix}
7   I                        ER S4   nodev        /lib/kernex.exp{/unix}
8   I                        ER S5   printf       /lib/kernex.exp{/unix}
9   I                        ER S6   uiomove      /lib/kernex.exp{/unix}
10  I                        ER S7   xmalloc      /lib/kernex.exp{/unix}
11  I                        ER S8   xmfree       /lib/kernex.exp{/unix}
12     00000000 0008B8  2 PR SD S9   <>     
/tmp/cliff/demodd/demodd.c(demodd.o)
13     00000000           PR LD S10  .democonfig
14     0000039C           PR LD S11  .demoopen
15     000004B4           PR LD S12  .democlose
16     000005D4           PR LD S13  .demoread
17     00000704           PR LD S14  .demowrite
18     00000830           PR LD S15  .get_dp
19     000008B8 000024  2 GL SD S16  <.printf>    glink.s(/usr/lib/glink.o)
20     000008B8           GL LD S17  .printf
21     000008DC 000024  2 GL SD S18  <.xmalloc>   glink.s(/usr/lib/glink.o)
22     000008DC           GL LD S19  .xmalloc
23     00000900 000090  2 PR SD S20  .bzero       
noname(/usr/lib/libcsys.a[bzero.o])
24     00000990 000024  2 GL SD S21  <.uiomove>   glink.s(/usr/lib/glink.o)
25     00000990           GL LD S22  .uiomove
26     000009B4 000024  2 GL SD S23  <.devswadd>  glink.s(/usr/lib/glink.o)
27     000009B4           GL LD S24  .devswadd
28     000009D8 000024  2 GL SD S25  <.devswdel>  glink.s(/usr/lib/glink.o)
29     000009D8           GL LD S26  .devswdel
30     000009FC 000024  2 GL SD S27  <.xmfree>    glink.s(/usr/lib/glink.o)
31     000009FC           GL LD S28  .xmfree
32     00000000 000444  4 RW SD S29  <_/tmp/cliff/demodd/demodd$c$>
/tmp/cliff/demodd/demodd.c(demodd.o)
33     00000450 000004  4 RW SD S30  demo_dev     
/tmp/cliff/demodd/demodd.c(demodd.o)
34     00000460 000004  4 RW SD S31  demos_inited 
/tmp/cliff/demodd/demodd.c(demodd.o)
35     00000470 000080  4 RW SD S32  data         
/tmp/cliff/demodd/demodd.c(demodd.o)
36 * E 000004F0 00000C  2 DS SD S33  democonfig   
/tmp/cliff/demodd/demodd.c(demodd.o)
37   E 000004FC 00000C  2 DS SD S34  demoopen     
/tmp/cliff/demodd/demodd.c(demodd.o)
38   E 00000508 00000C  2 DS SD S35  democlose    
/tmp/cliff/demodd/demodd.c(demodd.o)
39   E 00000514 00000C  2 DS SD S36  demoread     
/tmp/cliff/demodd/demodd.c(demodd.o)
40   E 00000520 00000C  2 DS SD S37  demowrite    
/tmp/cliff/demodd/demodd.c(demodd.o)
41     0000052C 000000  2 T0 SD S38  <TOC>
42     0000052C 000004  2 TC SD S39  <_/tmp/cliff/demodd/demodd$c$>
43     00000530 000004  2 TC SD S40  <printf>
44     00000534 000004  2 TC SD S41  <demo_dev>
45     00000538 000004  2 TC SD S42  <demos_inited>
46     0000053C 000004  2 TC SD S43  <data>
47     00000540 000004  2 TC SD S44  <pinned_heap>
48     00000544 000004  2 TC SD S45  <xmalloc>
49     00000548 000004  2 TC SD S46  <uiomove>
50     0000054C 000004  2 TC SD S47  <devswadd>
51     00000550 000004  2 TC SD S48  <devswdel>
52     00000554 000004  2 TC SD S49  <xmfree>

In the sample map file listed previously, the .data section starts from the statement at line 32:

32     00000000 000444  4 RW SD S29 <_/tmp/cliff/demodd/demodd$c$>
/tmp/cliff/demodd/demodd.c(demodd.o)

The TOC (Table of Contents) starts from the statement at line 41:

41     0000052C 000000  2 T0 SD S38 <TOC>
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