On 11 March 2014 20:51, Claudio Fontana hw.claudio@gmail.com wrote:

Hi Claudio,

I am building an ELF image using aarch64-linux-gnu-ld from linaro:

GNU ld (crosstool-NG linaro-1.13.1-4.8-2014.02 - Linaro GCC 2014.02) 2.24.0.20131220

I am linking in the libstc++.a, which contains in particular a GOT entry for __gthread_active_ptr that is of interest to me, pointing to __pthread_key_create, used for detecting pthread support for std::thread,

and while I get the relocations for the GOT itself in a .rela.dyn section, and a nice pointer to it from the dynamic section (RELA), the dynamic RELASZ entry contains zero:

Here is the comparison of the Dynamic section (note RELASZ) with the following .rela.dyn relocations:

loader.elf: file format elf64-littleaarch64 loader.elf architecture: aarch64, flags 0x00000112: EXEC_P, HAS_SYMS, D_PAGED start address 0x00000000400b0000

Program Header: LOAD off 0x0000000000000000 vaddr 0x0000000040090000 paddr 0x0000000040090000 align 2**16 filesz 0x0000000000407084 memsz 0x00000000004aa504 flags rwx TLS off 0x0000000000407080 vaddr 0x0000000040497080 paddr 0x0000000040497080 align 2**3 filesz 0x0000000000000004 memsz 0x0000000000000580 flags rw- DYNAMIC off 0x0000000000001000 vaddr 0x0000000040091000 paddr 0x0000000040091000 align 2**3 filesz 0x0000000000000120 memsz 0x0000000000000120 flags rw- EH_FRAME off 0x00000000003ce5fc vaddr 0x000000004045e5fc paddr 0x000000004045e5fc align 2**2 filesz 0x000000000000bae4 memsz 0x000000000000bae4 flags r-- NOTE off 0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**3 filesz 0x0000000000000000 memsz 0x0000000000000000 flags ---

Dynamic Section: NEEDED dummy-shlib.so INIT_ARRAY 0x00000000404841b8 INIT_ARRAYSZ 0x0000000000000330 HASH 0x000000004044bd58 STRTAB 0x00000000403e3320 SYMTAB 0x00000000403a4110 STRSZ 0x0000000000068a33 SYMENT 0x0000000000000018 DEBUG 0x0000000000000000 RELA 0x00000000404780c0 RELASZ 0x0000000000000000 RELAENT 0x0000000000000018 private flags = 0:

... 10 .rela.dyn 00002058 00000000404780c0 00000000404780c0 003e80c0 2**3 CONTENTS, ALLOC, LOAD, READONLY, DATA ... and now the .rela.dyn.relocations from aarch64-linux-gnu-readelf -r loader.elf :

Relocation section '.rela.dyn' at offset 0x3e80c0 contains 345 entries: Offset Info Type Sym. Value Sym. Name + Addend 0000404832d0 002b00000401 R_AARCH64_GLOB_DA 00000000405339c8 _ZNSt8time_getIwSt19is + 0 0000404832d8 004400000401 R_AARCH64_GLOB_DA 000000004047e450 _ZTISt7codecvtIcc11__m + 0 0000404832e0 004b00000401 R_AARCH64_GLOB_DA 00000000405338c8 _ZGVNSt8numpunctIcE2id + 0 0000404832e8 005800000401 R_AARCH64_GLOB_DA 000000004047c460 _ZTISt8messagesIcE + 0 0000404832f0 006200000401 R_AARCH64_GLOB_DA 000000004047df40 _ZTVSt9strstream + 0 0000404832f8 007200000401 R_AARCH64_GLOB_DA 00000000402870dc _ZNSt17bad_function_ca + 0 000040483300 008500000401 R_AARCH64_GLOB_DA 0000000040534e58 _ZGVN9__gnu_cxx16bitma + 0 000040483310 00c300000401 R_AARCH64_GLOB_DA 0000000040533a18 _ZNSt6locale2id11_S_re + 0 000040483318 00dd00000401 R_AARCH64_GLOB_DA 000000004047c160 _ZTISt5ctypeIwE + 0 000040483320 00ea00000401 R_AARCH64_GLOB_DA 0000000040534e18 _ZZN9__gnu_cxx9free_li + 0 000040483328 011700000401 R_AARCH64_GLOB_DA 0000000040533968 _ZGVNSt8time_getIwSt19 + 0 000040483330 013500000401 R_AARCH64_GLOB_DA 000000004047cfd8 _ZTISt7num_getIwSt19is + 0 000040483338 017300000401 R_AARCH64_GLOB_DA 000000004021d51c __pthread_key_create + 0

...

^^...note the __pthread_key_create relocation I am interested in...

I would expect the RELASZ in the dynamic section to be 0x2058 instead of 0.

Any tips to what could be wrong?

I can't see any obvious way this could happen from looking at the linker code. Do you have a method for reproducing the problem you could share? Or could you send me the binary?

Thanks,