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Relocations installed by the BPF ELF backend were sometimes incorrectly
adding the symbol value to the relocation entry addend, when the correct
relocation value was already stored in the addend. This could lead to a
relocation effectively adding the symbol value twice.
Fix that by making bpf_elf_generic_reloc () more similar to the flow of
bfd_install_relocation in the case where howto->install_addend is set,
which is how it ought to behave.
bfd/
* bpf-reloc.def (R_BPF_64_ABS32, R_BPF_64_ABS64)
(R_BPF_64_NODYLD32): Set partial_inplace to true.
* elf64-bpf.c (bpf_elf_generic_reloc): Do not include the value
of the symbol when installing relocation. Copy some additional
logic from bfd_elf_generic_reloc.
gas/
* testsuite/gas/bpf/bpf.exp: Run new test.
* testsuite/gas/bpf/elf-relo-1.d: New.
* testsuite/gas/bpf/elf-relo-1.s: New.
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This patch adds linker support to patch R_BPF_64_NODYLD32 relocations.
The implementation was based on comments and code in LLVM, as the GNU
toolchain does not uses this relocation type.
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This reverts commit 675b9d612cc59446e84e2c6d89b45500cb603a8d.
See https://sourceware.org/pipermail/binutils/2023-August/128761.html.
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CGEN is cool, but the BPF architecture is simply too bizarre for it.
The weird way of BPF to handle endianness in instruction encoding, the
weird C-like alternative assembly syntax, the weird abuse of
multi-byte (or infra-byte) instruction fields as opcodes, the unusual
presence of opcodes beyond the first 32-bits of some instructions, are
all examples of what makes it a PITA to continue using CGEN for this
port. The bpf.cpu file is becoming so complex and so nested with
p-macros that it is very difficult to read, and quite challenging to
update. Also, every time we are forced to change something in CGEN to
accommodate BPF requirements (which is often) we have to do extensive
testing to make sure we do not break any other target using CGEN.
This is getting un-maintenable.
So I have decided to bite the bullet and revamp/rewrite the port so it
no longer uses CGEN. Overall, this involved:
* To remove the cpu/bpf.{cpu,opc} descriptions.
* To remove the CGEN generated files.
* To replace the CGEN generated opcodes table with a new hand-written
opcodes table for BPF.
* To replace the CGEN generated disassembler wih a new disassembler
that uses the new opcodes.
* To replace the CGEN generated assembler with a new assembler that uses the
new opcodes.
* To replace the CGEN generated simulator with a new simulator that uses the
new opcodes. [This is pushed in GDB in another patch.]
* To adapt the build systems to the new situation.
Additionally, this patch introduces some extensions and improvements:
* A new BPF relocation BPF_RELOC_BPF_DISP16 plus corresponding ELF
relocation R_BPF_GNU_64_16 are added to the BPF BFD port. These
relocations are used for section-relative 16-bit offsets used in
load/store instructions.
* The disassembler now has support for the "pseudo-c" assembly syntax of
BPF. What dialect to use when disassembling is controlled by a command
line option.
* The disassembler now has support for dumping instruction immediates in
either octal, hexadecimal or decimal. The used output base is controlled
by a new command-line option.
* The GAS BPF test suite has been re-structured and expanded in order to
test the disassembler pseudoc syntax support. Minor bugs have been also
fixed there. The assembler generic tests that were disabled for bpf-*-*
targets due to the previous implementation of pseudoc syntax are now
re-enabled. Additional tests have been added to test the new features of
the assembler. .dump files are no longer used.
* The linker BPF test suite has been adapted to the command line options
used by the new disassembler.
The result is very satisfactory. This patchs adds 3448 lines of code
and removes 10542 lines of code.
Tested in:
* Target bpf-unknown-none with 64-bit little-endian host and 32-bit
little-endian host.
* Target x86-64-linux-gnu with --enable-targets=all
Note that I have not tested in a big-endian host yet. I will do so
once this lands upstream so I can use the GCC compiler farm.
I have not included ChangeLog entries in this patch: these would be
massive and not very useful, considering this is pretty much a rewrite
of the port. I beg the indulgence of the global maintainers.
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- Removed not needed relocations.
- Renamed relocations to match llvm and linux kernel.
Relocation changes:
R_BPF_INSN_64 => R_BPF_64_64
R_BPF_INSN_DISP32 => R_BPF_64_32
R_BPF_DATA_32 => R_BPF_64_ABS32
R_BPF_DATA_64 => R_BPF_64_ABS64
ChangeLog:
* bfd/bpf-reloc.def: Created file with BPF_HOWTO macro entries.
* bfd/reloc.c: Removed non needed relocations.
* bfd/bfd-in2.h: regenerated.
* bfd/libbfd.h: regenerated.
* bfd/elf64-bpf.c: Changed relocations.
* include/elf/bpf.h: Adapted relocation values/names.
* gas/config/tc-bpf.c: Changed relocation mapping.
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