diff options
author | Fangrui Song <maskray@google.com> | 2023-06-24 00:18:56 +0000 |
---|---|---|
committer | Daniel Borkmann <daniel@iogearbox.net> | 2023-06-29 15:46:17 +0200 |
commit | bbaf1ff06af49e856501024abbe161d96c1f0d66 (patch) | |
tree | 7dabb39068dd6e1a411e094c55d7d2c32581a0b1 /Documentation/bpf | |
parent | da1a055d01ed0c18402dd1f1934096ac4bb36ada (diff) |
bpf: Replace deprecated -target with --target= for Clang
The -target option has been deprecated since clang 3.4 in 2013. Therefore, use
the preferred --target=bpf form instead. This also matches how we use --target=
in scripts/Makefile.clang.
Signed-off-by: Fangrui Song <maskray@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Quentin Monnet <quentin@isovalent.com>
Link: https://github.com/llvm/llvm-project/commit/274b6f0c87a6a1798de0a68135afc7f95def6277
Link: https://lore.kernel.org/bpf/20230624001856.1903733-1-maskray@google.com
Diffstat (limited to 'Documentation/bpf')
-rw-r--r-- | Documentation/bpf/bpf_devel_QA.rst | 10 | ||||
-rw-r--r-- | Documentation/bpf/btf.rst | 4 | ||||
-rw-r--r-- | Documentation/bpf/llvm_reloc.rst | 6 |
3 files changed, 10 insertions, 10 deletions
diff --git a/Documentation/bpf/bpf_devel_QA.rst b/Documentation/bpf/bpf_devel_QA.rst index 609b71f5747d..de27e1620821 100644 --- a/Documentation/bpf/bpf_devel_QA.rst +++ b/Documentation/bpf/bpf_devel_QA.rst @@ -635,12 +635,12 @@ test coverage. Q: clang flag for target bpf? ----------------------------- -Q: In some cases clang flag ``-target bpf`` is used but in other cases the +Q: In some cases clang flag ``--target=bpf`` is used but in other cases the default clang target, which matches the underlying architecture, is used. What is the difference and when I should use which? A: Although LLVM IR generation and optimization try to stay architecture -independent, ``-target <arch>`` still has some impact on generated code: +independent, ``--target=<arch>`` still has some impact on generated code: - BPF program may recursively include header file(s) with file scope inline assembly codes. The default target can handle this well, @@ -658,7 +658,7 @@ independent, ``-target <arch>`` still has some impact on generated code: The clang option ``-fno-jump-tables`` can be used to disable switch table generation. -- For clang ``-target bpf``, it is guaranteed that pointer or long / +- For clang ``--target=bpf``, it is guaranteed that pointer or long / unsigned long types will always have a width of 64 bit, no matter whether underlying clang binary or default target (or kernel) is 32 bit. However, when native clang target is used, then it will @@ -668,7 +668,7 @@ independent, ``-target <arch>`` still has some impact on generated code: while the BPF LLVM back end still operates in 64 bit. The native target is mostly needed in tracing for the case of walking ``pt_regs`` or other kernel structures where CPU's register width matters. - Otherwise, ``clang -target bpf`` is generally recommended. + Otherwise, ``clang --target=bpf`` is generally recommended. You should use default target when: @@ -685,7 +685,7 @@ when: into these structures is verified by the BPF verifier and may result in verification failures if the native architecture is not aligned with the BPF architecture, e.g. 64-bit. An example of this is - BPF_PROG_TYPE_SK_MSG require ``-target bpf`` + BPF_PROG_TYPE_SK_MSG require ``--target=bpf`` .. Links diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst index 7cd7c5415a99..f32db1f44ae9 100644 --- a/Documentation/bpf/btf.rst +++ b/Documentation/bpf/btf.rst @@ -990,7 +990,7 @@ format.:: } g2; int main() { return 0; } int test() { return 0; } - -bash-4.4$ clang -c -g -O2 -target bpf t2.c + -bash-4.4$ clang -c -g -O2 --target=bpf t2.c -bash-4.4$ readelf -S t2.o ...... [ 8] .BTF PROGBITS 0000000000000000 00000247 @@ -1000,7 +1000,7 @@ format.:: [10] .rel.BTF.ext REL 0000000000000000 000007e0 0000000000000040 0000000000000010 16 9 8 ...... - -bash-4.4$ clang -S -g -O2 -target bpf t2.c + -bash-4.4$ clang -S -g -O2 --target=bpf t2.c -bash-4.4$ cat t2.s ...... .section .BTF,"",@progbits diff --git a/Documentation/bpf/llvm_reloc.rst b/Documentation/bpf/llvm_reloc.rst index e4a777a6a3a2..450e6403fe3d 100644 --- a/Documentation/bpf/llvm_reloc.rst +++ b/Documentation/bpf/llvm_reloc.rst @@ -28,7 +28,7 @@ For example, for the following code:: return g1 + g2 + l1 + l2; } -Compiled with ``clang -target bpf -O2 -c test.c``, the following is +Compiled with ``clang --target=bpf -O2 -c test.c``, the following is the code with ``llvm-objdump -dr test.o``:: 0: 18 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r1 = 0 ll @@ -157,7 +157,7 @@ and ``call`` instructions. For example:: return gfunc(a, b) + lfunc(a, b) + global; } -Compiled with ``clang -target bpf -O2 -c test.c``, we will have +Compiled with ``clang --target=bpf -O2 -c test.c``, we will have following code with `llvm-objdump -dr test.o``:: Disassembly of section .text: @@ -203,7 +203,7 @@ The following is an example to show how R_BPF_64_ABS64 could be generated:: int global() { return 0; } struct t { void *g; } gbl = { global }; -Compiled with ``clang -target bpf -O2 -g -c test.c``, we will see a +Compiled with ``clang --target=bpf -O2 -g -c test.c``, we will see a relocation below in ``.data`` section with command ``llvm-readelf -r test.o``:: |