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Diffstat (limited to 'Documentation/bpf/llvm_reloc.rst')
| -rw-r--r-- | Documentation/bpf/llvm_reloc.rst | 18 |
1 files changed, 10 insertions, 8 deletions
diff --git a/Documentation/bpf/llvm_reloc.rst b/Documentation/bpf/llvm_reloc.rst index ca8957d5b671..e4a777a6a3a2 100644 --- a/Documentation/bpf/llvm_reloc.rst +++ b/Documentation/bpf/llvm_reloc.rst @@ -48,7 +48,7 @@ the code with ``llvm-objdump -dr test.o``:: 14: 0f 10 00 00 00 00 00 00 r0 += r1 15: 95 00 00 00 00 00 00 00 exit -There are four relations in the above for four ``LD_imm64`` instructions. +There are four relocations in the above for four ``LD_imm64`` instructions. The following ``llvm-readelf -r test.o`` shows the binary values of the four relocations:: @@ -79,14 +79,16 @@ The following is the symbol table with ``llvm-readelf -s test.o``:: The 6th entry is global variable ``g1`` with value 0. Similarly, the second relocation is at ``.text`` offset ``0x18``, instruction 3, -for global variable ``g2`` which has a symbol value 4, the offset -from the start of ``.data`` section. - -The third and fourth relocations refers to static variables ``l1`` -and ``l2``. From ``.rel.text`` section above, it is not clear -which symbols they really refers to as they both refers to +has a type of ``R_BPF_64_64`` and refers to entry 7 in the symbol table. +The second relocation resolves to global variable ``g2`` which has a symbol +value 4. The symbol value represents the offset from the start of ``.data`` +section where the initial value of the global variable ``g2`` is stored. + +The third and fourth relocations refer to static variables ``l1`` +and ``l2``. From the ``.rel.text`` section above, it is not clear +to which symbols they really refer as they both refer to symbol table entry 4, symbol ``sec``, which has ``STT_SECTION`` type -and represents a section. So for static variable or function, +and represents a section. So for a static variable or function, the section offset is written to the original insn buffer, which is called ``A`` (addend). Looking at above insn ``7`` and ``11``, they have section offset ``8`` and ``12``. |