Hi H.J, Adhemerval, Szabolcs, > On Thu, Oct 7, 2021 at 7:18 AM Adhemerval Zanella via Libc-alpha > wrote: > > > > > > > > On 07/10/2021 07:00, Lukasz Majewski wrote: > > > On Thu, 7 Oct 2021 11:19:26 +0200 > > > Lukasz Majewski wrote: > > > > > >> 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. > > >> > > > > > > And indeed it is the case. Yocto/OE by default perform prelinking > > > (use prelink program) to speedup start time of dynamic program. > > > > > > The prelink [1] itself assigns some virtual addresses to all > > > required shared objects (in our case for /sbin/init), so no > > > clashes are encountered. > > > > > > And using prelink is a _default_ behaviour in Yocto/OE poky > > > distro. > > > > Does it work without prelink? Also, does it fail with prelink in > > real hardware? > > > > It indeed might be a prelink issue in fact. > > This will fail everywhere if prelink is used. > Do we have _any_ plan how to fix it? BSPs for many boards are built with Yocto/OE nowadays... The approach with using 'adr' (pseudo) assembler instruction to calculate the on-runtime addresses was working previously. Shall we revert changes which were introduced recently (to use __ehdr_start)? Best regards, Lukasz Majewski -- DENX Software Engineering GmbH, Managing Director: Wolfgang Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@denx.de