Section symbols exist as an optimization: instead of having multiple relocations
point to different symbols, many of them can point to a single section symbol.
When that optimization is unused, a section symbol is also unused and adds no
extra information to the object file.
This saves a bit of space on the object files and makes the output of
llvm-objdump -t easier to read and consequently some tests get quite a bit
simpler.
llvm-svn: 239045
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
Instead of accumulating the content in a fragment first, just write it
to the output stream.
Also put it first in the section table, so that we never have to worry
about its index being >= SHN_LORESERVE.
llvm-svn: 236145
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
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
ELF with support for:
- File headers
- Section headers + data
- Relocations
- Symbols
- Unwind data (only COFF/Win64)
The output format follows a few rules:
- Values are almost always output one per line (as elf-dump/coff-dump already do). - Many values are translated to something readable (like enum names), with the raw value in parentheses.
- Hex numbers are output in uppercase, prefixed with "0x".
- Flags are sorted alphabetically.
- Lists and groups are always delimited.
Example output:
---------- snip ----------
Sections [
Section {
Index: 1
Name: .text (5)
Type: SHT_PROGBITS (0x1)
Flags [ (0x6)
SHF_ALLOC (0x2)
SHF_EXECINSTR (0x4)
]
Address: 0x0
Offset: 0x40
Size: 33
Link: 0
Info: 0
AddressAlignment: 16
EntrySize: 0
Relocations [
0x6 R_386_32 .rodata.str1.1 0x0
0xB R_386_PC32 puts 0x0
0x12 R_386_32 .rodata.str1.1 0x0
0x17 R_386_PC32 puts 0x0
]
SectionData (
0000: 83EC04C7 04240000 0000E8FC FFFFFFC7 |.....$..........|
0010: 04240600 0000E8FC FFFFFF31 C083C404 |.$.........1....|
0020: C3 |.|
)
}
]
---------- snip ----------
Relocations and symbols can be output standalone or together with the section header as displayed in the example.
This feature set supports all tests in test/MC/COFF and test/MC/ELF (and I suspect all additional tests using elf-dump), making elf-dump and coff-dump deprecated.
Patch by Nico Rieck!
llvm-svn: 178679
Rafael Espindola