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
We already do this for shstrtab, so might as well do it for strtab. This
extracts the string table building code into a separate class. The idea
is to use it for other object formats too.
I mostly wanted to do this for the general principle, but it does save a
little bit on object file size. I tried this on a clang bootstrap and
saved 0.54% on the sum of object file sizes (1.14 MB out of 212 MB for
a release build).
Differential Revision: http://reviews.llvm.org/D3533
llvm-svn: 207670
When evaluating an assembly expression for a relocation, we want to
stop at MCSymbols that are in the symbol table, even if they are variables.
This is needed since the semantics may require that the relocation use them.
That is not the case when computing the value of a symbol in the symbol table.
There are no relocations in this case and we have to keep going until we hit
a section or find out that the expression doesn't have an assembly time
value.
llvm-svn: 207445
The symbol table itself has no relocations, so it is not possible to represent
things like
a = undefined + 1
With the patch we just omit these variables. That matches the behaviour of the
gnu assembler.
llvm-svn: 207419
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
Both ZLIB and the debug info compressed section header ("ZLIB" + the
size of the uncompressed data) take some constant overhead so in some
cases the compressed data is actually larger than the uncompressed data.
In these cases, just don't compress or rename the section at all.
llvm-svn: 206659
While unnamed relocations are already cached in side tables in
ELFObjectWriter::RecordRelocation, symbols still need their fragments
updated to refer to the newly compressed fragment (even if that fragment
isn't big enough to fit the offset). Even though we only create
temporary symbols in debug info sections this comes up in 32 bit builds
where even temporary symbols in mergeable sections (such as debug_str)
have to be emitted as named symbols.
I tried a few other ways to do this but they all didn't work for various
reasons:
1) Canonicalize the MCSymbolData in RecordRelocation, nulling out the
Fragment (so it didn't have to be updated by CompressDebugSection). This
doesn't work because some code relies on symbols having fragments to
indicate that they're defined, I think.
2) Canonicalize the MCSymbolData in RecordRelocation to be "first
fragment + absolute offset" so it would be cheaper to just test and
update the fragment in CompressDebugSections. This doesn't work because
the offset computed in RecordRelocation isn't that of the symbol's
fragment, it's the passed in fragment (I haven't figured out what that
fragment is - perhaps it's the location where the relocation is to be
written). And if the fragment offset has to be computed only for this
use we might as well just do it when we need to, in
CompressDebugSection.
I also added an assert to help catch this a bit more clearly, even
though it is UB. The test case improvements would either assert fail
and/or valgrind vail without the fix, even if they wouldn't necessarily
fail the FileCheck output.
llvm-svn: 206653
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
To support compressing the debug_line section that contains multiple
fragments (due, I believe, to variation in choices of line table
encoding depending on the size of instruction ranges in the actual
program code) we needed to support compressing multiple MCFragments in a
single pass.
This patch implements that behavior by mutating the post-relaxed and
relocated section to be the compressed form of its former self,
including renaming the section.
This is a more flexible (and less invasive, to a degree) implementation
that will allow for other features such as "use compression only if it's
smaller than the uncompressed data".
Compressing debug_frame would be a possible further extension to this
work, but I've left it for now. The hurdle there is alignment sections -
which might require going as far as to refactor
MCAssembler.cpp:writeFragment to handle writing to a byte buffer or an
MCObjectWriter (there's already a virtual call there, so it shouldn't
add substantial compile-time cost) which could in turn involve
refactoring MCAsmBackend::writeNopData to use that same abstraction...
which involves touching all the backends. This would remove the limited
handling of fragment writing seen in
ELFObjectWriter.cpp:getUncompressedData which would be nice - but it's
more invasive.
I did discover that I (perhaps obviously) don't need to handle
relocations when I rewrite the fragments - since the relocations have
already been applied and computed (and stored into
ELFObjectWriter::Relocations) by this stage (necessarily, because we
need to have written any immediate values or assembly-time relocations
into the data already before we compress it, which we have). The test
case doesn't necessarily cover that in detail - I can add more test
coverage if that's preferred.
llvm-svn: 205990
To support compression for debug_line and debug_frame a different
approach is required. To simplify review, revert the old implementation
and XFAIL the test case. New implementation to follow shortly.
Reverts r205059 and r204958.
llvm-svn: 205989
This moves one case of raw text checking down into the MCStreamer
interfaces in the form of a virtual function, even if we ultimately end
up consolidating on the one-or-many line tables issue one day, this is
nicer in the interim. This just generally streamlines a bunch of use
cases into a common code path.
llvm-svn: 205287
I don't think this is reachable by any frontend (why would you transform
asm to asm+debug info?) but it helps tidy up some of this code, avoid
the weird special case of "emit the first CU, store the label, then emit
the rest" in MCDwarfLineTable::Emit by instead having the
DWARF-for-assembly case use the same codepath as DwarfDebug.cpp, by
registering the label of the debug_line section, thus causing it to be
emitted. (with a special case in asm output to just emit the label since
asm output uses the .loc directives, etc, rather than the debug_loc
directly)
llvm-svn: 205286
When LLVM is not built with zlib, nocompression.s will test
for the error message. But this test case will cause breakage
because the exit code is non-zero. This commit fix this issue
by adding "not" to the command.
llvm-svn: 205102
I started trying to fix a small issue, but this code has seen a small fix too
many.
The old code was fairly convoluted. Some of the issues it had:
* It failed to check if a symbol difference was in the some section when
converting a relocation to pcrel.
* It failed to check if the relocation was already pcrel.
* The pcrel value computation was wrong in some cases (relocation-pc.s)
* It was missing quiet a few cases where it should not convert symbol
relocations to section relocations, leaving the backends to patch it up.
* It would not propagate the fact that it had changed a relocation to pcrel,
requiring a quiet nasty work around in ARM.
* It was missing comments.
llvm-svn: 205076
Turns out debug_frame does use multiple fragments, so it doesn't
compress correctly with the current approach. Disable compressing it for
now while I figure out what's the best solution for it.
llvm-svn: 205059
This is a bit of a stab in the dark, since I have zlib on my machine.
Just going to bounce it off the bots & see if it sticks.
Do we have some convention for negative REQUIRES: checks? Or do I just
need to add a feature like I've done here?
llvm-svn: 205050
1) When creating a .debug_* section and instead create a .zdebug_
section.
2) When creating a fragment in a .zdebug_* section, make it a compressed
fragment.
3) When computing the size of a compressed section, compress the data
and use the size of the compressed data.
4) Emit the compressed bytes.
Also, check that only if a section has a compressed fragment, then that
is the only fragment in the section.
Assert-fail if the fragment's data is modified after it is compressed.
Initial review on llvm-commits by Eric Christopher and Rafael Espindola.
llvm-svn: 204958
We need .symtab_shndxr if and only if a symbol references a section with an
index >= 0xff00.
The old code was trying to figure out if the section was needed ahead of time,
making it a fairly dependent on the code actually writing the table. It was
also somewhat conservative and would create the section in cases where it was
not needed.
If I remember correctly, the old structure was there so that the sections were
created in the same order gas creates them. That was valuable when MC's support
for ELF was new and we tested with elf-dump.py.
This patch refactors the symbol table creation to another class and makes it
obvious that .symtab_shndxr is really only created when we are about to output
a reference to a section index >= 0xff00.
While here, also improve the tests to use macros. One file is one section
short of needing .symtab_shndxr, the second one has just the right number.
llvm-svn: 204769
This is similar, but not identical to what gas does. The logic in MC is to just
compute the symbol table after parsing the entire file. GAS is mixed, given
.type b, @object
a = b
b:
.type b, @function
It will propagate the change and make 'a' a function. Given
.type b, @object
b:
a = b
.type b, @function
the type of 'a' is still object.
Since we do the computation in the end, we produce a function in both cases.
llvm-svn: 204555
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
The revision I'm reverting breaks handling of transitive aliases. This blocks us
and breaks sanitizer bootstrap:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap/builds/2651
(and checked locally by Alexey).
This revision is the result of:
svn merge -r204059:204058 -r204028:204027 -r203962:203961 .
+ the regression test added to test/MC/ELF/alias.s
Another way to reproduce the regression with clang:
$ cat q.c
void a1();
void a2() __attribute__((alias("a1")));
void a3() __attribute__((alias("a2")));
void a1() {}
$ ~/work/llvm-build/bin/clang-3.5-good -c q.c && mv q.o good.o && \
~/work/llvm-build/bin/clang-3.5-bad -c q.c && mv q.o bad.o && \
objdump -t good.o bad.o
good.o: file format elf64-x86-64
SYMBOL TABLE:
0000000000000000 l df *ABS* 0000000000000000 q.c
0000000000000000 l d .text 0000000000000000 .text
0000000000000000 l d .data 0000000000000000 .data
0000000000000000 l d .bss 0000000000000000 .bss
0000000000000000 l d .comment 0000000000000000 .comment
0000000000000000 l d .note.GNU-stack 0000000000000000 .note.GNU-stack
0000000000000000 l d .eh_frame 0000000000000000 .eh_frame
0000000000000000 g F .text 0000000000000006 a1
0000000000000000 g F .text 0000000000000006 a2
0000000000000000 g F .text 0000000000000006 a3
bad.o: file format elf64-x86-64
SYMBOL TABLE:
0000000000000000 l df *ABS* 0000000000000000 q.c
0000000000000000 l d .text 0000000000000000 .text
0000000000000000 l d .data 0000000000000000 .data
0000000000000000 l d .bss 0000000000000000 .bss
0000000000000000 l d .comment 0000000000000000 .comment
0000000000000000 l d .note.GNU-stack 0000000000000000 .note.GNU-stack
0000000000000000 l d .eh_frame 0000000000000000 .eh_frame
0000000000000000 g F .text 0000000000000006 a1
0000000000000000 g F .text 0000000000000006 a2
0000000000000000 g .text 0000000000000000 a3
llvm-svn: 204137
This is really a consistency fix. Since given
a = b
we propagate the information, we should propagate it too given
a = b + (1 - 1)
Fixes pr19145.
llvm-svn: 204028
This is implemented by handling assignments to the '.' pseudo symbol
as ".org" directives.
Differential Revision: http://llvm-reviews.chandlerc.com/D2625
llvm-svn: 201530
Summary:
This adds support for emitting DWARF path discriminator values in
the object streamer. It also changes the DWARF dumper to show
discriminator values in the line table output.
Reviewers: echristo
CC: llvm-commits
Differential Revision: http://llvm-reviews.chandlerc.com/D2794
llvm-svn: 201427
This commit allows LLVM MC to process .cfi_startproc directives when
they are followed by an additional `simple' identifier. This signals to
elide the emission of target specific CFI instructions that would
normally occur initially.
This fixes PR16587.
Differential Revision: http://llvm-reviews.chandlerc.com/D2624
llvm-svn: 200227
