RE: [EXT] Re: help! why a 'so' can't load its dependent 'so' to the pre-defined address

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Hi Kewen,

Thanks for your detailed instructions, 
Following your idea, but with a minor difference, instead of -T scriptfile, I am using -Wl,-Ttext-segment=0xXXXXXXXX(e.g. 0x70000000),


ldd libtestScript.so
        linux-vdso.so.1 (0x0000007fa6f04000)
        libcpss.so => ./libcpss.so (0x0000000010000000)
        libhelper.so => ./libhelper.so (0x0000000014600000)
        libpthread.so.0 => /lib/aarch64-linux-gnu/libpthread.so.0 (0x0000007fa6ece000)
        librt.so.1 => /lib/aarch64-linux-gnu/librt.so.1 (0x0000007fa6eb7000)
        libdl.so.2 => /lib/aarch64-linux-gnu/libdl.so.2 (0x0000007fa6ea2000)
        libm.so.6 => /lib/aarch64-linux-gnu/libm.so.6 (0x0000007fa6de6000)
        libc.so.6 => /lib/aarch64-linux-gnu/libc.so.6 (0x0000007fa6c8d000)
        /lib/ld-linux-aarch64.so.1 (0x0000005565c4c000)

readelf -h libtestScript.so
ELF Header:
  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF64
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              DYN (Shared object file)
  Machine:                           AArch64
  Version:                           0x1
  Entry point address:               0x70000840
  Start of program headers:          64 (bytes into file)
  Start of section headers:          7248 (bytes into file)
  Flags:                             0x0
  Size of this header:               64 (bytes)
  Size of program headers:           56 (bytes)
  Number of program headers:         6
  Size of section headers:           64 (bytes)
  Number of section headers:         28
  Section header string table index: 25


Cheers, 
Kewen, appreciate so much for your kind help !!!


Xinghao Chen (陈行浩)

-----Original Message-----
From: Kewen.Lin <linkw@xxxxxxxxxxxxx> 
Sent: 2019年12月17日 10:42
To: Xing-Hao Chen <ericxh@xxxxxxxxxxx>; gcc-help@xxxxxxxxxxx
Subject: Re: [EXT] Re: help! why a 'so' can't load its dependent 'so' to the pre-defined address

on 2019/12/16 下午4:13, Xing-Hao Chen wrote:
> Hi Kewen,
> Appreciate very much for your reply,
>  
> "I found that if you force the virtual address for the libtestScript.so generation as well, you can see the expected result you wanted."
> 
> But how to force the VA for libtestScript.so? 
> I tried "-Wl,-Ttext=0xXXXX", but will suffer some link problems. 
> How can I assign the 0xXXXX, while fixing the load VA of libcpss.so/libhelper.so(to be 0x10000000 / 0x14600000) which libtestScript.so relies on?
> 

Hi,

I think you can still use linker script scheme for libtestScript.so generation like what you have for libcpss.so/libhelper.so.  I used linker script for libt1.so libt3.so generation and see the ldd dump as below.  Here libt3 is like libtestScript.so, libt1 is like libcpss.so/libhelper.so and libt2 is as normal.

$ LD_LIBRARY_PATH=. ldd ./libt3.so
        linux-vdso64.so.1 =>  (0x00003fffadb40000)
        libt1.so => ./libt1.so (0x0000020000000000)
        libt2.so => ./libt2.so (0x00003fffadb10000)
        libc.so.6 => /lib/powerpc64le-linux-gnu/libc.so.6 (0x00003fffad910000)
        /lib64/ld64.so.2 (0x00003fffadb60000)

** simple ld scripts **
ld01.txt:
  SECTIONS
  {
    . = 0x20000000000;
    .text : { *(.text) }
  }
ld03.txt:
SECTIONS
  {
    . = 0x40000000000;
    .text : { *(.text) }
  }

PS: above scripts are really simple, just for proof of concepts.

** commands **
gcc -shared -fPIC t1.c -o libt1.so -Tld01.txt gcc -shared -fPIC t2.c -o libt2.so gcc -shared -fPIC t3.c -o libt3.so -Tld03.txt -L. -lt1 -lt2 -Wl,-R.
gcc main.c -L. -lt3

Note that you need to avoid that the module libtestScript.so conflicts with libcpss.so/libhelper.so, for example using ld01.txt for libt3.so generation, it gets the dumping as below.

$ LD_LIBRARY_PATH=. ldd ./libt3.so
        linux-vdso64.so.1 =>  (0x00003fffb0550000)
        libt1.so => ./libt1.so (0x00003fffa0540000)
        libt2.so => ./libt2.so (0x00003fffa0510000)
        libc.so.6 => /lib/powerpc64le-linux-gnu/libc.so.6 (0x00003fffa0310000)
        /lib64/ld64.so.2 (0x00003fffb0570000)

** simple src **
t1.c:
  int t1(int a, int b) { return a + b; }
t2.c:
  int t2(int a, int b) { return a - b; }
t3.c:
  extern int t1(int a, int b);
  extern int t2(int a, int b);
  int t3(int a, int b){
    return t1(a, b) + t2(b, a);
  }
main.c:
  extern int t3(int a, int b);
  int main() {
    int a = 1;
    int b = 2;
    int c = t3(a+b, b-a);
    return c;
  }

I tested it on powerpc64le-linux-gnu, with gcc 5.4.0 and GNU ld 2.26.1, FYI in case it matters.

BR,
Kewen

> In summary of my requirement -
> When loading libtestScript.so, the loader should load its dependent 
> two so(libcpss.so/libhelper.so) into the pre-defined VA(to be 
> 0x10000000 / 0x14600000)
> 
> How can I do?  Any suggestion is appreciated. 
> 





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