Hi Szabolcs,

> The 10/06/2021 13:43, Lukasz Majewski wrote:
> > Please find in-depth analyze about the issue:
> > 
> > It was tested with Beagle Bone Black (BBB) and QEMU (the same binary
> > rootfs images).
> > (If needed I will upload images and script to run QEMU to some
> > server for reproduction).
> > Branch: https://github.com/lmajewski/y2038_glibc/commits/y2038_edge
> >  
> 
> i think it is easier to look at if you upload the broken
> ld.so binary. or at least readelf -aW ld.so output.

Please find working and broken ld-linux-armhf.so.3:
https://owncloud.denx.de/s/wtAfktG6pXLffSA

> 
> > On working setup to trigger the core dump:
> > /home/root/ld-linux-armhf.so.3 /sbin/init
> > gdb ./ld-linux-armhf.so.3 core
> > 
> > (and the /home/root/ld-linux-armhf.so.3 is the "broken" one).
> > 
> > 
> > Not working (patch [1] not applied):
> > ====================================
> > 
> > All the code is located in _dl_start in elf/rtld.c and
> > elf/get-dynamic-info.h files:
> > 
> > (gdb) p/x $r5
> > $46 = 0xb6fc8000
> > r5 is set from the elf_machine_load_address()
> > 
> > Then we enter the elf_get_dynamic_info()
> > 
> > 0xb6fc95fc      99            ADJUST_DYN_INFO (DT_SYMTAB);
> >    0xb6fc95f8 <_dl_start+308>:  04 30 92 15     ldrne   r3, [r2,
> > #4] => 0xb6fc95fc <_dl_start+312>:  05 30 83 10     addne   r3, r3,
> > r5 0xb6fc9600 <_dl_start+316>:  04 30 82 15     strne   r3, [r2, #4]
> > (gdb) p/x $r3
> > $63 = 0x410003f4
> > (gdb) p/x $r5
> > $64 = 0xb6fc8000  
> 
> it seems r5 is already wrong here, it's not the runtime
> address of 0. (looks more like the runtime address of
> 0x41000000)

The r5 is set according to the change in patch which now I'm trying to
fix.

To be more specific - r5 is set according to code in patch SHA1:
bca0f5cbc9257c13322b99e55235c4f21ba0bd82

> 
> likely something goes wrong with the computation of r5.

Before the SHA1: bca0f5cbc9257c13322b99e55235c4f21ba0bd82 patch r5 was
computed with using 'adr' assembler instruction, not set from some
constant value.

asm ("adr %0, _dl_start" : "=r" (pcrel_addr));

And r5 value was 0x75fc8000

> 
> > Links:
> > [1] -
> > https://github.com/lmajewski/y2038_glibc/commit/e67e0f589b88a44be8f8b9b770b08950dd7e5bd5
> > 
> > readelf -e ld-linux-armhf.so.3 
> > 
> > [10] .plt              PROGBITS        41000994 000994 000050 04
> > AX  0   0  4 [11] .text             PROGBITS        41000a00 000a00
> > 01fed0 00  AX  0   0 64 [12] .rodata           PROGBITS
> > 410208d0 0208d0 004b24 00   A  0   0  4 [13] .ARM.extab
> > PROGBITS        410253f4 0253f4 000018 00   A  0   0  4 [14]
> > .ARM.exidx        ARM_EXIDX       4102540c 02540c 0000c8 00  AL 11
> >  0  4 [15] .data.rel.ro      PROGBITS        41036200 026200 000cf4
> > 00  WA  0   0  8 [16] .dynamic          DYNAMIC         41036ef4
> > 026ef4 0000c8 08  WA  5   0  4 [17] .got              PROGBITS
> >   41036fbc 026fbc 000040 04  WA  0   0  4  
> 
> why are all addresses >0x41000000 ?
> in a shared library i expect all those addresses
> to be close to 0.

On this real HW system (the rootfs which is running) - libc.so.6 also
has address > 0x41000000
libm.so.6 also has the value > 0x41200000
(Entry point address:               0x412c9190)

The offset of > 0x41000000 looks a bit strange indeed, but it is still
less than the kernel space. Moreover, with position independent code it
shall not matter.

> 
> is this made by some modified binutils?

I've double checked the ld-linux-armhf.so.3 and after build it has:
(Entry point address:               0xa00) which seems to be correct.

So it looks like during installation of the glibc (on the Yocto/OE
created rootfs) the elf header is modified and this 0x41000000 offset is
added.


Best regards,

Lukasz Majewski

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