Home Original page

[AArch64] Relax TLS local dynamic traditional into local executable

Jiong Wang jiong.wang@arm.com
Tue Aug 25 13:05:00 GMT 2015 
This patch add the linker relaxation from TLS local dynamic traditional
model into local executable on AArch64 tiny/small model.

After this relaxation, we don't need to invoke the runtime resolver.

The linker relaxation logic will be:

Code sequence I (tiny):

    0x00 adr  x0, :tlsldm:x
    0x04 bl   __tls_get_addr
         |
         V
    0x00 mrs  x0, tpidr_el0
    0x04 add  x0, x0, TCB_SIZE

Code sequence II (small):

    0x00 adrp a0, :tlsldm:x
    0x04 add  a0, #:tlsldm_lo12:x
    0x08 bl   __tls_get_addr
         |
         V
    0x00 mrs  x0, tpidr_el0
    0x04 add  x0, x0, TCB_SIZE
    0x08 nop

For local dynamic model, the TLS instruction sequences is composed of
two parts, the first part calcuate module base address, the second part
add variable offset to get final address.

For linker relaxation, we only need to touch the first part. When relax
from local dynamic into local executable, we don't need to invoke
runtime resolver to get module base address. As for local executable,
the "module" should be initial TLS module, thus the module base address
can be calculated by "tp + TCB_SIZE" as tp points to start of initial
TLS module start, we need to skip the thread control block to point to
real module contents for variable.

After the relaxation, the relocation for the 'bl' instruction should be
removed also, as we don't need any relocation anymore.

ok for trunk?

2015-08-25  Jiong Wang  <jiong.wang@arm.com>

bfd/
  * elfnn-aarch64.c (aarch64_tls_transition_without_check): Support
  three TLS local dynamic traditional relocations types.
  (elfNN_aarch64_tls_relax): Support TLS local dynamic traditional to
  local executable relaxation.

ld/testsuite/
  * ld-aarch64/tls-relax-ld-le-tiny.s: New testcase.
  * ld-aarch64/tls-relax-ld-le-small.s: Likewise.
  * ld-aarch64/tls-relax-ld-le-tiny.d: New expectation file.
  * ld-aarch64/tls-relax-ld-le-small.d: Likewise.
  * ld-aarch64/aarch64-elf.exp: Run new testcases.
  
-- 
Regards,
Jiong

-------------- next part --------------
A non-text attachment was scrubbed...
Name: lerelax.patch
Type: text/x-diff
Size: 6271 bytes
Desc: not available
URL: <https://sourceware.org/pipermail/binutils/attachments/20150825/b586af26/attachment.bin>
More information about the Binutils mailing list