This fixes several issues. The behavior changes are:
A SHN_COMMON symbol does not have the 'g' flag.
An undefined symbol does not have 'g' or 'l' flag.
A STB_GLOBAL SymbolRef::ST_Unknown symbol has the 'g' flag.
A STB_LOCAL SymbolRef::ST_Unknown symbol has the 'l' flag.
Reviewed By: rupprecht
Differential Revision: https://reviews.llvm.org/D75659
Summary:
rL371826 rearranged some output from llvm-objdump for GNU objdump compatability, but there still seem to be some more.
I think this rearrangement is a little closer. Overview of the ordering which matches GNU objdump:
* Archive headers
* File headers
* Section headers
* Symbol table
* Dwarf debugging
* Relocations (if `--disassemble` is not used)
* Section contents
* Disassembly
Reviewers: jhenderson, justice_adams, grimar, ychen, espindola
Reviewed By: jhenderson
Subscribers: aprantl, emaste, arichardson, jrtc27, atanasyan, seiya, llvm-commits, MaskRay
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68066
llvm-svn: 373671
Old: PT_LOAD(.data | PT_GNU_RELRO(.data.rel.ro .bss.rel.ro) | .bss)
New: PT_LOAD(PT_GNU_RELRO(.data.rel.ro .bss.rel.ro) | .data .bss)
The placement of | indicates page alignment caused by PT_GNU_RELRO. The
new layout has simpler rules and saves space for many cases.
Old size: roundup(.data) + roundup(.data.rel.ro)
New size: roundup(.data.rel.ro + .bss.rel.ro) + .data
Other advantages:
* At runtime the 3 memory mappings decrease to 2.
* start(PT_TLS) = start(PT_GNU_RELRO) = start(RW PT_LOAD). This
simplifies binary manipulation tools.
GNU strip before 2.31 discards PT_GNU_RELRO if its
address is not equal to the start of its associated PT_LOAD.
This has been fixed by https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=f2731e0c374e5323ce4cdae2bcc7b7fe22da1a6f
But with this change, we will be compatible with GNU strip before 2.31
* Before, .got.plt (non-relro by default) was placed before .got (relro
by default), which made it impossible to have _GLOBAL_OFFSET_TABLE_
(start of .got.plt on x86-64) equal to the end of .got (R_GOT*_FROM_END)
(https://bugs.llvm.org/show_bug.cgi?id=36555). With the new ordering, we
can improve on this regard if we'd like to.
Reviewers: ruiu, espindola, pcc
Subscribers: emaste, arichardson, llvm-commits, joerg, jdoerfert
Differential Revision: https://reviews.llvm.org/D56828
llvm-svn: 356117
Almost all entries inside MIPS GOT are referenced by signed 16-bit
index. Zero entry lies approximately in the middle of the GOT. So the
total number of GOT entries cannot exceed ~16384 for 32-bit architecture
and ~8192 for 64-bit architecture. This limitation makes impossible to
link rather large application like for example LLVM+Clang. There are two
workaround for this problem. The first one is using the -mxgot
compiler's flag. It enables using a 32-bit index to access GOT entries.
But each access requires two assembly instructions two load GOT entry
index to a register. Another workaround is multi-GOT. This patch
implements it.
Here is a brief description of multi-GOT for detailed one see the
following link https://dmz-portal.mips.com/wiki/MIPS_Multi_GOT.
If the sum of local, global and tls entries is less than 64K only single
got is enough. Otherwise, multi-got is created. Series of primary and
multiple secondary GOTs have the following layout:
```
- Primary GOT
Header
Local entries
Global entries
Relocation only entries
TLS entries
- Secondary GOT
Local entries
Global entries
TLS entries
...
```
All GOT entries required by relocations from a single input file
entirely belong to either primary or one of secondary GOTs. To reference
GOT entries each GOT has its own _gp value points to the "middle" of the
GOT. In the code this value loaded to the register which is used for GOT
access.
MIPS 32 function's prologue:
```
lui v0,0x0
0: R_MIPS_HI16 _gp_disp
addiu v0,v0,0
4: R_MIPS_LO16 _gp_disp
```
MIPS 64 function's prologue:
```
lui at,0x0
14: R_MIPS_GPREL16 main
```
Dynamic linker does not know anything about secondary GOTs and cannot
use a regular MIPS mechanism for GOT entries initialization. So we have
to use an approach accepted by other architectures and create dynamic
relocations R_MIPS_REL32 to initialize global entries (and local in case
of PIC code) in secondary GOTs. But ironically MIPS dynamic linker
requires GOT entries and correspondingly ordered dynamic symbol table
entries to deal with dynamic relocations. To handle this problem
relocation-only section in the primary GOT contains entries for all
symbols referenced in global parts of secondary GOTs. Although the sum
of local and normal global entries of the primary got should be less
than 64K, the size of the primary got (including relocation-only entries
can be greater than 64K, because parts of the primary got that overflow
the 64K limit are used only by the dynamic linker at dynamic link-time
and not by 16-bit gp-relative addressing at run-time.
The patch affects common LLD code in the following places:
- Added new hidden -mips-got-size flag. This flag required to set low
maximum size of a single GOT to be able to test the implementation using
small test cases.
- Added InputFile argument to the getRelocTargetVA function. The same
symbol referenced by GOT relocation from different input file might be
allocated in different GOT. So result of relocation depends on the file.
- Added new ctor to the DynamicReloc class. This constructor records
settings of dynamic relocation which used to adjust address of 64kb page
lies inside a specific output section.
With the patch LLD is able to link all LLVM+Clang+LLD applications and
libraries for MIPS 32/64 targets.
Differential revision: https://reviews.llvm.org/D31528
llvm-svn: 334390
On MIPS .got section cannot be included into the PT_GNU_RELRO segment.
Sometimes it might work, but in general it is unsupported. One of the
problem is that all sections marked by SHF_MIPS_GPREL should be grouped
together because data in these sections is addressable with a gp
relative address, but such sections might be writable.
This patch exclude mips .got from PT_GNU_RELRO segment and group
SHF_MIPS_GPREL sections.
llvm-svn: 292161
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
This patch allows static linking of TLS code. To do that it fixes
GOT entries initialization.
If TLS-related GOT entry created for a preemptible symbol i.e. has
a corresponding dynamic relocation, leave the entry initialized by zero.
Write down adjusted TLS symbol's values otherwise. For the adjustments
calculation use offsets for thread-local storage.
https://www.linux-mips.org/wiki/NPTL
llvm-svn: 280914
On most architectures the linker is required to optimize away any
references to __tls_get_addr in case of static linking. As usual
a special case is MIPS - libc defines __tls_get_addr itself because
there are no TLS optimizations for this architecture.
llvm-svn: 280664
Fangrui Song