Currently LLD prints basename of source file name in error messages,
for example:
$ mkdir foo
$ echo 'void _start(void) { foobar(); }' > foo/bar.c
$ gcc -g -c foo/bar.c
$ bin/ld.lld -o out bar.o
bin/ld.lld: error: bar.c:1: undefined symbol 'foobar'
$
This should say:
bin/ld.lld: error: foo/bar.c:1: undefined symbol 'foobar'
This is PR31299
Differential revision: https://reviews.llvm.org/D27506
llvm-svn: 288966
This patch refactor how to apply the R_AARCH64_LDST{8,16,32,64,128}_ABS_NC
relocations by adding a new function to correct extract the bits expected
by each relocation. This make is explicit which are the bits range expected
and simplify the code to mask and shift the deriable values.
It also fixes the R_AARCH64_LDST128_ABS_LO12_NC mask, although in pratice
the mask/shift always returns a 16 bytes aligned value.
Checked on AArch64 and with test-suite.
llvm-svn: 288921
Shared libraries should have entry set following the same rules as for
regular binaries. The only difference is that in case the default entry
point (_start or __start) isn't found (unless it was set explicitly), we
shouldn't give a warning as in case of regular binaries.
Differential Revision: https://reviews.llvm.org/D27497
llvm-svn: 288878
If we do, the freebsd dynamic linker tries to call mmap with a size 0,
which fails.
It is hard to avoid creating them when linker scripts are used, so we
just delete empty PT_LOADs at the end.
llvm-svn: 288808
For preemptable symbols the dynamic linker does all the work. Trying
to compute the addend is at best wasteful and can also lead to crashes
in cases of programs that uses tls but doesn't define any tls
variables.
llvm-svn: 288803
This change seems to make LLD 0.6% faster when linking Clang with
debug info. I don't want us to have lots of local optimizations,
but this function is very hot, and the improvement is small but
not negligible, so I think it's worth doing.
llvm-svn: 288757
On Linux (and probably on other Unix-like systems), unlink(2) is
noticeably slow. It takes 250 milliseconds to remove a 1 GB file
on ext4 filesystem on my machine, whether the file is on SSD or
on a spinning disk.
To create a new result file, we remove existing file first. So, if
you repeatedly link a 1 GB program in a regular compile-link-debug
cycle, every cycle wastes 250 milliseconds only to remove a file.
Since LLD can link a 1 GB in about 5 seconds, that waste actually
matters.
This patch defines `unlinkAsync` function. The function spawns a
background thread to call unlink. The calling thread returns
almost immediately.
Differential Revision: https://reviews.llvm.org/D27295
llvm-svn: 288680
The relocation R_AARCH64_LDST16_ABS_LO12_NC should set a ld/st
immediate value to bits [11:1] not [11:2]. This patches fixes it
and adds a testcase for regression.
With this fix all the faulty tests on test-suite (clavm, lencod,
and trimaran) pass.
llvm-svn: 288670
I removed a wrong optimization for ICF in r288527. Sean Silva suggested
in a post commit review that the correct algorithm can be implemented
easily. So is this patch.
llvm-svn: 288620
Some elf producers (dtrace) put this flag in relocation sections and
some (MC) don't. If we don't ignore the flag we end up with multiple
relocation sections poiting to the same section, which we don't
support.
llvm-svn: 288585
A program or object file using R_386_8, R_386_16, R_386_PC16 or R_386_PC8
relocations is not conformant to latest ABI. The R_386_16, and R_386_8
relocations truncate the computed value to 16 - bits and 8 - bits
respectively. R_386_PC16 and R_386_16 are used by some
applications, for example by FreeBSD loaders.
Previously we did not take addend in account for these relocation,
counting it as 0, what is wrong and was a reason of hangs.
This patch needed for example for FreeBSD pmbr (protective mbr).
Differential revision: https://reviews.llvm.org/D27303
llvm-svn: 288581
Binary output feature is a bit confuzing. bfd and gold output differs a lot sometimes,
though it is important for FreeBSD mbr loaders.
Patch change the way how we compute file offsets for binary output.
This fixes PR31196.
Previously offsets were calculated basing on offsets and addresses of sections
from the same loads:
if (Sec == First)
return alignTo(Off, Target->MaxPageSize, Sec->Addr);
return First->Offset + Sec->Addr - First->Addr;
bfd assigns offsets for each section to VA - MinVA:
https://github.com/redox-os/binutils-gdb/blob/master/bfd/binary.c#L27https://github.com/redox-os/binutils-gdb/blob/master/bfd/binary.c#L255
(LMA == VA usually)
This patch for now just stops creating phdrs for binary output.
An effect from this that no any additional calculation for offset is performed:
uintX_t getFileAlignment(uintX_t Off, OutputSectionBase *Sec) {
OutputSectionBase *First = Sec->FirstInPtLoad;
// If the section is not in a PT_LOAD, we have no other constraint.
if (!First)
return Off; //**First is always null, condition always happens**
That is enough now with combination of another patch to generate output
that is similar to what bfd produce for mbr loader.
Differential revision: https://reviews.llvm.org/D27341
llvm-svn: 288580
--omagic is an option to create old-fashioned executables in which
.text segments are writable. Today, the option is still in use to
create special-purpose programs such as boot loaders. It doesn't
make sense to create PT_GNU_RELRO for such executables.
DIfferential revision: https://reviews.llvm.org/D27297
llvm-svn: 288579
This is a hack for single thread execution. We are using Color[0] and
Color[1] alternately on each iteration. This optimization is to look
at the next slot as opposted to the current slot to get recent results
early. Turns out that the assumption is wrong, because the other slots
are not always have the most recent values, but instead it may have
stale values of the previous iteration. This patch removes that
performance hack.
llvm-svn: 288527
The assertion asserted that colorable sections can never have
a reference to non-colorable sections, but that was simply wrong.
They can have references to non-colorable sections. If that's the
case, referenced sections must be the same in terms of pointer
comparison.
llvm-svn: 288511
LLD used to take 11.73 seconds to link Clang. Now it is 6.94 seconds.
MSVC link takes 83.02 seconds. Note that ICF is enabled by default on
Windows, so a low latency ICF is more important than in ELF.
llvm-svn: 288487
It looks like the way dtrace works is
* The user creates .o files that reference magical symbol names.
* dtrace reads those files, collecs the info it needs and changes the
relocation to R_X86_64_NONE expecting the linker to ignore them.
llvm-svn: 288485
Associative sections are sections that need to be linked if their associated
sections are linked. Associative sections are used to append auxiliary data
such as debug info.
Previously, we compared all associative sections when comparing two comdat
sections. Because usually assocative sections are not mergeable sections,
we missed a lot of mergeable sections. MSVC linker doesn't seem to check
the identity of associative sections.
This patch makes LLD to ignore associative sections when doing ICF.
llvm-svn: 288483
r288228 seems to have regressed ICF performance in some cases in which
a lot of sections are actually mergeable. In r288228, I made a change
to create a Range object for each new color group. So every time we
split a group, we allocated and added a new group to a list of groups.
This patch essentially reverted r288228 with an improvement to
parallelize the original algorithm.
Now the ICF main loop is entirely allocation-free and lock-free.
Just like pre-r288228, we search for group boundaries by linear scan
instead of managing the information using Range class. r288228 was
neutral in performance-wise, and so is this patch.
I confirmed that this produces the exact same result as before
using chromium and clang as tests.
llvm-svn: 288480
This is a fairly reasonable bfd extension since there is one obvious value.
dtrace depends on this feature as it creates multiple absolute
symbols with the same value.
llvm-svn: 288461
ICF is short for Identical Code Folding. It is a size optimization to
identify two or more functions that happened to have the same contents
to merges them. It usually reduces output size by a few percent.
ICF is slow because it is computationally intensive process. I tried
to paralellize it before but failed because I couldn't make a
parallelized version produce consistent outputs. Although it didn't
create broken executables, every invocation of the linker generated
slightly different output, and I couldn't figure out why.
I think I now understand what was going on, and also came up with a
simple algorithm to fix it. So is this patch.
The result is very exciting. Chromium for example has 780,662 input
sections in which 20,774 are reducible by ICF. LLD previously took
7.980 seconds for ICF. Now it finishes in 1.065 seconds.
As a result, LLD can now link a Chromium binary (output size 1.59 GB)
in 10.28 seconds on my machine with ICF enabled. Compared to gold
which takes 40.94 seconds to do the same thing, this is an amazing
number.
From here, I'll describe what we are doing for ICF, what was the
previous problem, and what I did in this patch.
In ICF, two sections are considered identical if they have the same
section flags, section data, and relocations. Relocations are tricky,
becuase two relocations are considered the same if they have the same
relocation type, values, and if they point to the same section _in
terms of ICF_.
Here is an example. If foo and bar defined below are compiled to the
same machine instructions, ICF can (and should) merge the two,
although their relocations point to each other.
void foo() { bar(); }
void bar() { foo(); }
This is not an easy problem to solve.
What we are doing in LLD is some sort of coloring algorithm. We color
non-identical sections using different colors repeatedly, and sections
in the same color when the algorithm terminates are considered
identical. Here is the details:
1. First, we color all sections using their hash values of section
types, section contents, and numbers of relocations. At this moment,
relocation targets are not taken into account. We just color
sections that apparently differ in different colors.
2. Next, for each color C, we visit sections having color C to see
if their relocations are the same. Relocations are considered equal
if their targets have the same color. We then recolor sections that
have different relocation targets in new colors.
3. If we recolor some section in step 2, relocations that were
previously pointing to the same color targets may now be pointing to
different colors. Therefore, repeat 2 until a convergence is
obtained.
Step 2 is a heavy operation. For Chromium, the first iteration of step
2 takes 2.882 seconds, and the second iteration takes 1.038 seconds,
and in total it needs 23 iterations.
Parallelizing step 1 is easy because we can color each section
independently. This patch does that.
Parallelizing step 2 is tricky. We could work on each color
independently, but we cannot recolor sections in place, because it
will break the invariance that two possibly-identical sections must
have the same color at any moment.
Consider sections S1, S2, S3, S4 in the same color C, where S1 and S2
are identical, S3 and S4 are identical, but S2 and S3 are not. Thread
A is about to recolor S1 and S2 in C'. After thread A recolor S1 in
C', but before recolor S2 in C', other thread B might observe S1 and
S2. Then thread B will conclude that S1 and S2 are different, and it
will split thread B's sections into smaller groups wrongly. Over-
splitting doesn't produce broken results, but it loses a chance to
merge some identical sections. That was the cause of indeterminism.
To fix the problem, I made sections have two colors, namely current
color and next color. At the beginning of each iteration, both colors
are the same. Each thread reads from current color and writes to next
color. In this way, we can avoid threads from reading partial
results. After each iteration, we flip current and next.
This is a very simple solution and is implemented in less than 50
lines of code.
I tested this patch with Chromium and confirmed that this parallelized
ICF produces the identical output as the non-parallelized one.
Differential Revision: https://reviews.llvm.org/D27247
llvm-svn: 288373
In various places in LLD's hot loops, we have expressions of the form
"E == R_FOO || E == R_BAR || ..." (E is a RelExpr).
Some of these expressions are quite long, and even though they usually go just
a very small number of ways and so should be well predicted, they can still
occupy branch predictor resources harming other parts of the code, or they
won't be predicted well if they overflow branch predictor resources or if the
branches are too dense and the branch predictor can't track them all (the
compiler can in theory avoid this, at a cost in text size). And some of these
expressions are so large and executed so frequently that even when
well-predicted they probably still have a nontrivial cost.
This speedup should be pretty portable. The cost of these simple bit tests is
independent of:
- the target we are linking for
- the distribution of RelExpr's for a given link (which can depend on how the
input files were compiled)
- what compiler was used to compile LLD (it is just a simple bit test;
hopefully the compiler gets it right!)
- adding new target-dependent relocations (e.g. needsPlt doesn't pay any extra
cost checking R_PPC_PLT_OPD on x86-64 builds)
I did some rough measurements on clang-fsds and this patch gives over about 4%
speedup for a regular -O1 link, about 2.5% for -O3 --gc-sections and over 5%
for -O0. Sorry, I don't have my current machine set up for doing really
accurate measurements right now.
This also is just a bit cleaner. Thanks for Joerg for suggesting for
this approach.
Differential Revision: https://reviews.llvm.org/D27156
llvm-svn: 288314
- Rename currentBuffer -> getCurrentMB to start it with verb.
- Simplify containsString.
- Add llvm_unreachable at end of getCurrentMB.
llvm-svn: 288310
Previously, on each iteration in ICF, we scan the entire vector of
input sections to find boundaries of groups having the same ID.
This patch changes the algorithm so that we now have a vector of ranges.
Each range contains a starting index and an ending index of the group.
So we no longer have to search boundaries on each iteration.
Performance-wise, this seems neutral. Instead of searching boundaries,
we now have to maintain ranges. But I think this is more readable
than the previous implementation.
Moreover, this makes easy to parallelize the main loop of ICF,
which I'll do in a follow-up patch.
llvm-svn: 288228
StringRefZ is a class to represent a null-terminated string. String
length is computed lazily, so it's more efficient than StringRef to
represent strings in string table.
The motivation of defining this new class is to merge functions
that only differ in string types; we have many constructors that takes
`const char *` or `StringRef`. With StringRefZ, we can merge them.
Differential Revision: https://reviews.llvm.org/D27037
llvm-svn: 288172
The module index dynamic relocation R_ARM_DTPMOD32 is always 1 for an
executable. When static linking and when we know that we are not a shared
object we can resolve the module index relocation statically.
The logic in handleNoRelaxTlsRelocation remains the same for Mips as it
has its own custom GOT writing code. For ARM we add the module index
relocation to the GOT when it can be resolved statically.
In addition the type of the RelExpr for the static resolution of TlsGotRel
should be R_TLS and not R_ABS as we need to include the size of
the thread control block in the calculation.
Addresses the TLS part of PR30218.
Differential revision: https://reviews.llvm.org/D27213
llvm-svn: 288153
When -O0 is specified, we do not do section merging.
Though before this patch several sections were generated instead
of single, what is useless.
Differential revision: https://reviews.llvm.org/D27041
llvm-svn: 288151
This change continues what was started by D27040
Now all allocatable synthetics should be available from script side.
Differential revision: https://reviews.llvm.org/D27131
llvm-svn: 288150
The MipsGotSection::getPageEntryOffset calculates index of GOT entry
with a "page" address. Previously this method changes the state
of MipsGotSection because it modifies PageIndexMap field. That leads
to the unpredictable results if getPageEntryOffset called from multiple threads.
The patch makes getPageEntryOffset constant. To do so it calculates GOT
entry index but does not update PageIndexMap field. Later in the
MipsGotSection::writeTo method linker calculates "page" addresses and
writes them to the output.
llvm-svn: 288129
If output section which referenced by R_MIPS_GOT_PAGE or R_MIPS_GOT16
relocations is small (less that 0x10000 bytes) and occupies two adjacent
0xffff-bytes pages, current formula gives incorrect number of required "page"
GOT entries. The problem is that in time of calculation we do not know
the section address and so we cannot calculate number of 0xffff-bytes
pages exactly.
This patch fix the formula. Now it gives a correct number of pages in
the worst case when "small" section intersects 0xffff-bytes page
boundary. From the other side, sometimes it adds one more redundant GOT
entry for each output section. But usually number of output sections
referenced by GOT relocations is small.
llvm-svn: 288127
-N (-omagic)
Set the text and data sections to be readable and writable.
Also, do not page-align the data segment.
Differential revision: https://reviews.llvm.org/D26888
llvm-svn: 288123
Right now we just remember a SymbolBody for each got entry and
duplicate a bit of logic to decide what value, if any, should be
written for that SymbolBody.
With ARM there will be more complicated values, and it seems better to
just use the relocation code to fill the got entries. This makes it
clear that each entry is filled by the dynamic linker or by the static
linker.
llvm-svn: 288107
That unifies handling cases when we have SECTIONS and when
-no-rosegment is given in compareSectionsNonScript()
Now Config->SingleRoRx is used for check, testcase is provided.
llvm-svn: 288022
Previously Config->SingleRoRx was set in
createFiles() and used HasSections.
This change moves it to readConfigs at place of
common flags handling, and adds logic that sets
this flag separatelly from ScriptParser if SECTIONS present.
llvm-svn: 288021
--no-rosegment: Do not put read-only non-executable sections in their own segment
Differential revision: https://reviews.llvm.org/D26889
llvm-svn: 288020
Unfortunatelly PT_ARM_EXIDX is special. There is no way to create it
from linker scripts, so we have to create it even if PHDRS is used.
This matches bfd and is required for the lld output to survive bfd's strip.
llvm-svn: 288012
Unfortunatelly some scripts look like
kernphys = ...
. = ....
and the expectation in that every orphan section is after the
assignment.
llvm-svn: 287996
This is an horrible special case, but seems to match bfd's behaviour
and is important for avoiding placing an orphan section before the
expected start of the file.
llvm-svn: 287994
They return new vectors, but at the same time they mutate other vectors,
so returning values doesn't make much sense. We should just mutate two
vectors.
llvm-svn: 287979
-color-diagnostics=auto is default because that's the same as
Clang's default. When color is enabled, error or warning messages
are colored like this.
error:
<bold>ld.lld</bold> <red>error:</red> foo.o: no such file
warning:
<bold>ld.lld</bold> <magenta>warning:</magenta> foo.o: no such file
Differential Revision: https://reviews.llvm.org/D27117
llvm-svn: 287949
Uncompressing section contents and spliting mergeable section contents
into smaller chunks are heavy tasks. They scan entire section contents
and do CPU-intensive tasks such as uncompressing zlib-compressed data
or computing a hash value for each section piece.
Luckily, these tasks are independent to each other, so we can do that
in parallel_for_each. The number of input sections is large (as opposed
to the number of output sections), so there's a large parallelism here.
Actually the current design to call uncompress() and splitIntoPieces()
in batch was chosen with doing this in mind. Basically what we need to
do here is to replace `for` with `parallel_for_each`.
It seems this patch improves latency significantly if linked programs
contain debug info (which in turn contain lots of mergeable strings.)
For example, the latency to link Clang (debug build) improved by 20% on
my machine as shown below. Note that ld.gold took 19.2 seconds to do
the same thing.
Before:
30801.782712 task-clock (msec) # 3.652 CPUs utilized ( +- 2.59% )
104,084 context-switches # 0.003 M/sec ( +- 1.02% )
5,063 cpu-migrations # 0.164 K/sec ( +- 13.66% )
2,528,130 page-faults # 0.082 M/sec ( +- 0.47% )
85,317,809,130 cycles # 2.770 GHz ( +- 2.62% )
67,352,463,373 stalled-cycles-frontend # 78.94% frontend cycles idle ( +- 3.06% )
<not supported> stalled-cycles-backend
44,295,945,493 instructions # 0.52 insns per cycle
# 1.52 stalled cycles per insn ( +- 0.44% )
8,572,384,877 branches # 278.308 M/sec ( +- 0.66% )
141,806,726 branch-misses # 1.65% of all branches ( +- 0.13% )
8.433424003 seconds time elapsed ( +- 1.20% )
After:
35523.764575 task-clock (msec) # 5.265 CPUs utilized ( +- 2.67% )
159,107 context-switches # 0.004 M/sec ( +- 0.48% )
8,123 cpu-migrations # 0.229 K/sec ( +- 23.34% )
2,372,483 page-faults # 0.067 M/sec ( +- 0.36% )
98,395,342,152 cycles # 2.770 GHz ( +- 2.62% )
79,294,670,125 stalled-cycles-frontend # 80.59% frontend cycles idle ( +- 3.03% )
<not supported> stalled-cycles-backend
46,274,151,813 instructions # 0.47 insns per cycle
# 1.71 stalled cycles per insn ( +- 0.47% )
8,987,621,670 branches # 253.003 M/sec ( +- 0.60% )
148,900,624 branch-misses # 1.66% of all branches ( +- 0.27% )
6.747548004 seconds time elapsed ( +- 0.40% )
llvm-svn: 287946
The function was used only within Relocations.cpp, but now we are
using it in many places, so this patch moves it to a file that fits
to the functionality.
llvm-svn: 287943
This is important for cases like:
.sdata : {
*(.got.plt .got)
...
}
That was not supported before as there was no way to get access to
synthetic sections from script.
More details on review page.
Differential revision: https://reviews.llvm.org/D27040
llvm-svn: 287913
This patch changes the error message from
too many errors emitted, stopping now
to
too many errors emitted, stopping now (use -error-limit=0 to see all errors)
Thanks for Sean for the suggestion!
llvm-svn: 287900
The .ARM.exidx table has an entry for each function with the first entry
giving the start address of the function, the table is sorted in ascending
order of function address. Given a PC value, the unwinder will search the
table for the entry that contains the PC value.
If the table entry happens to be the last, the range of the addresses that
the final unwinding table describes will extend to the end of the address
space. To prevent an incorrect address outside the address range of the
program matching the last entry we follow ld.bfd's example and add a
sentinel EXIDX_CANTUNWIND entry at the end of the table. This gives the
final real table entry an upper bound.
In addition the llvm libunwind unwinder currently depends on the presence
of a sentinel entry (PR31091).
Differential revision: https://reviews.llvm.org/D26977
llvm-svn: 287869
rL287555 introduces a link error when building with BUILD_SHARED_LIBS:
undefined reference to llvm::codeview::CVSymbolDumper::dump(),
and more...
The functions are available in libDebugInfoCodeView, from LLVM.
Patch by Visoiu Mistrih Francis!
llvm-svn: 287837
Previously, if a symbol specified by -e or ENTRY() is not found,
we didn't set entry point address. That is incompatible with GNU
because GNU linkers set the first address of .text to entry.
This patch implement that behavior.
llvm-svn: 287836
Offset between beginning of a .got section and _gp symbols used in MIPS
GOT relocations calculations. Usually the expression looks like
VA + Offset - GP, where VA is the .got section address, Offset - offset
of the GOT entry, GP - offset between .got and _gp. Also there two "magic"
symbols _gp_disp and __gnu_local_gp which hold the offset mentioned above.
These symbols might be referenced by MIPS relocations.
Now the linker always defines _gp symbol and uses hardcoded value for
its initialization. So offset between .got and _gp is 0x7ff0. The _gp_disp
and __gnu_local_gp defined if required and initialized by 0x7ff0.
In fact that is not correct because _gp symbol might be defined by a linker
script and holds arbitrary value. In that case we need to use this value
in relocation calculation and initialize _gp_disp and __gnu_local_gp
properly.
The patch fixes the problem and completes fixing the bug #30311.
https://llvm.org/bugs/show_bug.cgi?id=30311
Differential revision: https://reviews.llvm.org/D27036
llvm-svn: 287832
This is in the context of https://llvm.org/bugs/show_bug.cgi?id=31109.
When LLD prints out errors for relocations, it tends to print out
extremely large number of errors (like millions) because it would
print out one error per relocation.
This patch makes LLD bail out if it prints out more than 20 errors.
You can configure the limitation using -error-limit argument.
-error-limit=0 means no limit.
I chose the flag name because Clang has the same feature as -ferror-limit.
"f" doesn't make sense to us, so I omitted it.
Differential Revision: https://reviews.llvm.org/D26981
llvm-svn: 287789
We have different functions to stringize objects to construct
error messages. For InputFile, we have getFilename, and for
InputSection, we have getName. You had to memorize them.
I think this is the case where the function overloading comes in handy.
This patch defines toString() functions that are overloaded for all these
types, so that you just call it in error().
Differential Revision: https://reviews.llvm.org/D27030
llvm-svn: 287787
Align to the large page size (known as a superpage or huge page).
FreeBSD automatically promotes large, superpage-aligned allocations.
Differential Revision: https://reviews.llvm.org/D27042
llvm-svn: 287782
An upcoming change to the image base address for x86-64 (D27042) will
will change some addresses and hence the instruction encodings. We care
about the disassembled instructions, not their encodings.
Differential Revision: https://reviews.llvm.org/D27056
llvm-svn: 287778
There are two ways to set symbol versions. One way is to use symbol
definition file, and the other is to embed version names to symbol
names. In the latter way, symbol name is in the form of `foo@version1`
where `foo` is a real name and `version1` is a version.
We were parsing symbol names in insert(). That seems unnecessarily
too early. We can do it later after we resolve all symbols. Doing it
lazily is a good thing because it makes code easier to read
(because now we have a separate pass to parse symbol names). Also
it could slightly improve performance because if two identical symbols
have versions, we now parse them only once.
llvm-svn: 287741
For now MipsGotSection class is not ready for concurrent access from
multiple threads. The problem is in the getPageEntryOffset method. It
changes state of MipsGotSection object and might be called from
different threads at the same time. So turn Threads off for this target.
It's a temporary solution. The patch fixes MipsGotSection::getPageEntryOffset
is almost ready.
Differential revision: https://reviews.llvm.org/D27035
llvm-svn: 287740
Previously, we stored offsets in string tables to symbols, so
you needed to pass a string table to get a symbol name. This patch
stores const char pointers instead to eliminate the need to pass
a string table.
llvm-svn: 287737
Rui Ueyama