The _gp_disp symbol designates offset between start of function and 'gp'
pointer into GOT. The following code is a typical MIPS function preamble
used to setup $gp register:
lui $gp, %hi(_gp_disp)
addi $gp, $gp, %lo(_gp_disp)
To calculate R_MIPS_HI16 / R_MIPS_LO16 relocations results we use
the following formulas:
%hi(_gp - P + A)
%lo(_gp - P + A + 4),
where _gp is a value of _gp symbol, A is addend, and P current address.
The R_MIPS_LO16 relocation references _gp_disp symbol is always the second
instruction. That is why we need four byte adjustments. The patch assigns
R_PC type for R_MIPS_LO16 relocation and adjusts its addend by 4. That fix
R_MIPS_LO16 calculation.
For details see p. 4-19 at ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
Differential Revision: http://reviews.llvm.org/D19115
llvm-svn: 266368
This simplifies the code by allowing us to remove the visibility argument
to functions that create synthetic symbols.
The only functional change is that the visibility of the MIPS "_gp" symbol
is now hidden. Because this symbol is defined in every executable or DSO, it
would be difficult to observe a visibility change here.
Differential Revision: http://reviews.llvm.org/D19033
llvm-svn: 266208
Our symbol representation was redundant, and some times would get out of
sync. It had an Elf_Sym, but some fields were copied to SymbolBody.
Different parts of the code were checking the bits in SymbolBody and
others were checking Elf_Sym.
There are two general approaches to fix this:
* Copy the required information and don't store and Elf_Sym.
* Don't copy the information and always use the Elf_Smy.
The second way sounds tempting, but has a big problem: we would have to
template SymbolBody. I started doing it, but it requires templeting
*everything* and creates a bit chicken and egg problem at the driver
where we have to find ELFT before we can create an ArchiveFile for
example.
As much as possible I compared the test differences with what gold and
bfd produce to make sure they are still valid. In most cases we are just
adding hidden visibility to a local symbol, which is harmless.
In most tests this is a small speedup. The only slowdown was scylla
(1.006X). The largest speedup was clang with no --build-id, -O3 or
--gc-sections (i.e.: focus on the relocations): 1.019X.
llvm-svn: 265293
The `_gp_disp` is a magic symbol designates offset between start of
function and gp pointer into GOT. Only `R_MIPS_HI16` and `R_MIPS_LO16`
relocations are permitted with `_gp_disp`. The patch adds the `_gp_disp`
as an ignored symbol and adjusts symbol value before call the `relocateOne`
for `R_MIPS_HI16/LO16` relocations.
Differential Revision: http://reviews.llvm.org/D15480
llvm-svn: 255768
Simon Atanasyan