Previously, the code we set to our .plt entries expected that .got
and .got.plt are consecutive in the virtual address space.
Since %ebx points to the last entry of .got for position-independent
code, it assumed that .got is accessible with small negative
displacements and .got.plt are accessible with small positive
displacements.
That assumption was simply wrong. We don't impose any restrictions on
relative layout of .got and .got.plt. As a result, the control is
transferred to a bogus address from .plt at runtime, which resulted in
segfaults.
This patch removes that wrong assumption. We still assume that .got.plt
has a fixed relative address to .got, but we no longer assume that they
are consecutive in memory.
With this change, a "hello world" program compiled with -fPIC works.
Fixes https://bugs.llvm.org/show_bug.cgi?id=31332.
Differential Revision: https://reviews.llvm.org/D31682
llvm-svn: 299553
This is in preparation for my next change, which will introduce a relro
nobits section. That requires that relro sections appear at the end of the
progbits part of the r/w segment so that the relro nobits section can appear
contiguously.
Because of the amount of churn required in the test suite, I'm making this
change separately.
llvm-svn: 291523
-pie
--pic-executable
Create a position independent executable. This is currently only
supported on ELF platforms. Position independent executables are
similar to shared libraries in that they are relocated by the
dynamic linker to the virtual address the OS chooses for them
(which can vary between invocations). Like normal dynamically
linked executables they can be executed and symbols defined in the
executable cannot be overridden by shared libraries.
Differential revision: http://reviews.llvm.org/D18183
llvm-svn: 263693
Before this patch sections that go after relro sequence were placed at
the same memory page with relro ones. It caused segmentation fault on
freebsd.
Fixes PR25790.
Patch by George Rimar with some tweaks by myself.
llvm-svn: 256334
If R_386_PLT32 relocation is applied against symbol that can not be preempted then it can be resolved statically.
Patch implements it for x86 target.
Differential revision: http://reviews.llvm.org/D15376
llvm-svn: 255233
Patch implements lazy relocations for x86.
One of features of x86 is that executable files and shared object files have separate procedure linkage tables. So patch implements both cases.
Detailed information about instructions used can be found in http://docs.oracle.com/cd/E19620-01/805-3050/chapter6-1235/index.html (search: x86: Procedure Linkage Table).
Differential revision: http://reviews.llvm.org/D14955
llvm-svn: 254098
Rui Ueyama