When a symbol S shows up in an expression in assembly there are two
possible interpretations
* The expression is referring to the value of S in this file.
* The expression is referring to the value after symbol resolution.
In the first case the assembler can reason about the value and try to
produce a relocation.
In the second case, that is only possible if the symbol cannot be
preempted.
Assemblers are not very consistent about which interpretation gets used.
This changes MC to agree with GAS in the case of an expression of the
form "Sym - WeakSym".
llvm-svn: 258329
This extends the work done in r233995 so that now getFragment (in addition to
getSection) also works for variable symbols.
With that the existing logic to decide if a-b can be computed works even if
a or b are variables. Given that, the expression evaluation can avoid expanding
variables as aggressively and that in turn lets the relocation code see the
original variable.
In order for this to work with the asm streamer, there is now a dummy fragment
per section. It is used to assign a section to a symbol when no other fragment
exists.
This patch is a joint work by Maxim Ostapenko andy myself.
llvm-svn: 249303
The ELF spec is very clear:
-----------------------------------------------------------------------------
If the value is non-zero, it represents a string table index that gives the
symbol name. Otherwise, the symbol table entry has no name.
--------------------------------------------------------------------------
In particular, a st_name of 0 most certainly doesn't mean that the symbol has
the same name as the section.
llvm-svn: 238899
We have to avoid converting a reference to a global into a reference to a local,
but it is fine to look past a local.
Patch by Vasileios Kalintiris.
I just moved the comment and added thet test.
llvm-svn: 235300
Part of pr23272.
A small annoyance with the assembly syntax we implement is that given an
expression there is no way to know if what is desired is the value of that
expression for the symbols in this file or for the final values of those
symbols in a link.
The first case is useful for use in sections that get discarded or ignored
if the section they are describing is discarded.
For axample, consider A-B where A and B are in the same comdat section.
We can compute the value of the difference in the section that is present in
the current .o and if that section survives to the final DSO the value will
still will be correct.
But the section is in a comdat. Another section from another object file
might be used istead. We know that that section will define A and B, but
we have no idea what the value of A-B might be.
In practice we have to assume that the intention is to compute the value
in the current section since otherwise the is no way to create something like
the debug aranges section.
llvm-svn: 235222
The main differences are:
* Split in 32 and 64 bit functions.
* First switch on the Modifier so that we have only one non fully covered
switch.
* Map the fixup kind first to a x86_64 (or i386) specific enum, to make
it easy to handle cases like X86::reloc_riprel_4byte_movq_load.
* Switch on IsPCRel last, which reduces code duplication.
Fixes pr22308.
llvm-svn: 232837
The fix itself is fairly simple: move getAccessVariant to MCValue so that we
replace the old weak expression evaluation with the far more general
EvaluateAsRelocatable.
This then requires that EvaluateAsRelocatable stop when it finds a non
trivial reference kind. And that in turn requires the ELF writer to look
harder for weak references.
Last but not least, this found a case where we were being bug by bug
compatible with gas and accepting an invalid input. I reported pr19647
to track it.
llvm-svn: 207920
With this MC is able to handle _GLOBAL_OFFSET_TABLE_ in 64 bit mode, which is
needed for medium and large code models.
This fixes pr19470.
llvm-svn: 206793
This allows correct relocations to be generated for a symbolic
address that is being adjusted by a negative constant. Since r204294,
such expressions have triggered undefined behavior when LLVM was built
without assertions.
Credit goes to Rafael for this patch; I'm submitting it on his behalf
as he is on vacation this week.
llvm-svn: 206192
Given
bar = foo + 4
.long bar
MC would eat the 4. GNU as includes it in the relocation. The rule seems to be
that a variable that defines a symbol is used in the relocation and one that
does not define a symbol is evaluated and the result included in the relocation.
Fixing this unfortunately required some other changes:
* Since the variable is now evaluated, it would prevent the ELF writer from
noticing the weakref marker the elf streamer uses. This patch then replaces
that with a VariantKind in MCSymbolRefExpr.
* Using VariantKind then requires us to look past other VariantKind to see
.weakref bar,foo
call bar@PLT
doing this also fixes
zed = foo +2
call zed@PLT
so that is a good thing.
* Looking past VariantKind means that the relocation selection has to use
the fixup instead of the target.
This is a reboot of the previous fixes for MC. I will watch the sanitizer
buildbot and wait for a build before adding back the previous fixes.
llvm-svn: 204294
Summary:
LLVM would crash when trying to come up with a relocation type for
assembly like:
movabsq $V@TPOFF, %rax
Instead, we say the relocation type is R_X86_64_TPOFF64.
Fixes PR17274.
Reviewers: dblaikie, nrieck, rafael
CC: llvm-commits
Differential Revision: http://llvm-reviews.chandlerc.com/D1717
llvm-svn: 191163
For COFF and MachO, sections semantically have relocations that apply to them.
That is not the case on ELF.
In relocatable objects (.o), a section with relocations in ELF has offsets to
another section where the relocations should be applied.
In dynamic objects and executables, relocations don't have an offset, they have
a virtual address. The section sh_info may or may not point to another section,
but that is not actually used for resolving the relocations.
This patch exposes that in the ObjectFile API. It has the following advantages:
* Most (all?) clients can handle this more efficiently. They will normally walk
all relocations, so doing an effort to iterate in a particular order doesn't
save time.
* llvm-readobj now prints relocations in the same way the native readelf does.
* probably most important, relocations that don't point to any section are now
visible. This is the case of relocations in the rela.dyn section. See the
updated relocation-executable.test for example.
llvm-svn: 182908
The failures in r116753 r116756 were caused by a python issue -
Python likes to append 'L' suffix to stringified numbers if the number
is larger than a machine int. Unfortunately, this causes a divergence of
behavior between 32 and 64 bit python versions.
I re-crafted elf-dump/common_dump to take care of these issues by:
1. always printing 0x (makes for easy sed/regex)
2. always print fixed length (exactly 2 + numBits/4 digits long)
by mod ((2^numBits) - 1)
3. left-padded with '0'
There is a residual common routine that is also used by
macho-dump (dataToHex) , so I left the 'section_data' test values alone.
llvm-svn: 116823
With this patch in
movq $foo, foo(%rip)
foo:
.long foo
We produce a R_X86_64_32S for the first relocation and R_X86_64_32 for the
second one.
llvm-svn: 115134
