RTL arm load failed

[Chris Johns]

On 2/11/2014 8:28 pm, Peng Fan wrote:
>
> qemu-system-arm -no-reboot -net none -nographic -M realview-pbx-a9 -m
> 256M -kernel `find . -name dl01.exe` -s -S
>
> *** BEGIN OF TEST libdl (RTL) Loader 1 ***
> load: /dl-o1.o
> rtl: unsupported section: 15: type=1879048195 flags=00
> handle: 0x212b10 has unresolved externals
>

Thanks for the testing.

> dl-o1.o can not be correctly loaded, because of unresolved symbols.
> I do some debug using remote gdb and found it is the reloc entry
> references local symbols named "LCx" saying "LC0", "LC1", "LC2".
>
> Freenix at linux-jyl1:~/per/new/build-arm> arm-rtems4.11-readelf -s `find .
> -name dl-o1.o`
>
> Symbol table '.symtab' contains 22 entries:
>     Num:    Value  Size Type    Bind   Vis      Ndx Name
>       0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND
>       1: 00000000     0 FILE    LOCAL  DEFAULT  ABS dl-o1.c
>       2: 00000000     0 SECTION LOCAL  DEFAULT    1
>       3: 00000000     0 SECTION LOCAL  DEFAULT    3
>       4: 00000000     0 SECTION LOCAL  DEFAULT    4
>       5: 00000000     0 SECTION LOCAL  DEFAULT    5
>       6: 00000000     0 NOTYPE  LOCAL  DEFAULT    5 $d
> *     7: 00000000     0 NOTYPE  LOCAL  DEFAULT    5 .LC0*
> *     8: 00000020     0 NOTYPE  LOCAL  DEFAULT    5 .LC1*
> *     9: 00000068     0 NOTYPE  LOCAL  DEFAULT    5 .LC2*
>      10: 00000000     0 NOTYPE  LOCAL  DEFAULT    1 $t
>      11: 00000000     0 SECTION LOCAL  DEFAULT    6
>      12: 00000000     0 SECTION LOCAL  DEFAULT    8
>      13: 00000000     0 SECTION LOCAL  DEFAULT    9
>      14: 00000000     0 SECTION LOCAL  DEFAULT   11
>      15: 00000000     0 SECTION LOCAL  DEFAULT   13
>      16: 00000010     0 NOTYPE  LOCAL  DEFAULT   16 $d
>      17: 00000000     0 SECTION LOCAL  DEFAULT   16
>      18: 00000000     0 SECTION LOCAL  DEFAULT   14
>      19: 00000000     0 SECTION LOCAL  DEFAULT   15
>      20: 00000001    88 FUNC    GLOBAL DEFAULT    1 rtems_main
>      21: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND printf
>
> The LCx symbols's type is NOTYPE and not included in the rtl symbol
> table(local symbol may should not be included). In rtl-elf.c, line 387
> see following, the LCx symbols are not included, so fails. I prefer that
> if unresolved symbols detected in rtl, detailed info should be print
> out, but i found no debug msg about this.

Unresolved symbols may not be an error. If you have 2 files dependent on 
each other one will be loaded with unresolved externals until the other 
is loaded. The loader handles this and when the second dependent module 
is loaded the unresolved symbols are resolved. This means the loader is 
not in a position to have a clear enough picture to decide if there are 
unresolved symbols. The application loading must decide when to check, 
check and raise an error when it thinks there should be no errors.

>
> 384     /*
> 385      * Only keep the functions and global or weak symbols.
> 386      */
> 387     if ((ELF_ST_TYPE (symbol.st_info) == STT_OBJECT) ||
> 388         (ELF_ST_TYPE (symbol.st_info) == STT_FUNC))
>
> I think this cause arm load failed.

Interesting. Nothing has changed here as ELF should always have these 
symbols. It must be this test does something our testing before did not 
highlight.

I also suspect we will have issues with the RAP files. Let me explain. 
The code that was in my personal repo placed all global and local 
symbols into a single 'externals' symbol table. This worked because we 
had the awk hack to create the base image symbol table that used nm and 
nm only provided the global symbols. When I came to do the rtems-syms 
tool that takes a base kernel image and creates an exported symbols 
table I incorrectly ended up with the local symbols of the kernel in the 
symbol table and embedding that symbol table in the base image via the 
double link pass method failed on the second link. As a result I cleaned 
up the symbol code to have the rld::symbols classes load symbols into 
separate global, weak and local table. I suspect the RAP code is now 
only referencing the global table and so local symbols are not being 
included in the symbol table. I need to review this code.

> FYI, rap file are not included in the dl test?

This is coming as I have time. It is needed.

Chris