| Message ID | 20241002235253.487251-1-stephen.s.brennan@oracle.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | BPF |
| Headers | show |
On Wed, Oct 02, 2024 at 04:52:42PM -0700, Stephen Brennan wrote: > Hello all, > > This is v3 of the series to add global variables to pahole's generated BTF. > Patches 1-3 of v2 were already merged. This series splits the last patch of v2 > and does some small updates. It should apply cleanly to the "next" branch. > https://github.com/acmel/dwarves/commits/btf_global_vars/ > > Changes since v2: > 1. Split things out into several smaller patches as can be seen in the log > below. thanks for the split, so much better for review, lgtm Acked-by: Jiri Olsa <jolsa@kernel.org> thanks, jirka > 2. Previously the global_var feature was defined with BTF_DEFAULT_FEATURE, but I > think we agreed in the discussion of v2 that it would be better as > BTF_NON_DEFAULT_FEATURE, so I changed it to align with our discussion. > 3. Removed the "--encode_btf_global_vars" option. > 3. I went through and straightened out my use of integer types for ELF section > index (size_t, as returned by libelf) as well as the variable addr and size. > To this end I did add a few checks to explicitly ensure we don't overflow the > uint32_t fields in the DATASEC. > > To test this out on a Linux build, you'll want to make the following change: > > --------- > diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf > index b75f09f3f424..c88d9e526426 100644 > --- a/scripts/Makefile.btf > +++ b/scripts/Makefile.btf > @@ -19,7 +19,7 @@ pahole-flags-$(call test-ge, $(pahole-ver), 125) += --skip_encoding_btf_inconsis > else > > # Switch to using --btf_features for v1.26 and later. > -pahole-flags-$(call test-ge, $(pahole-ver), 126) = -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs > +pahole-flags-$(call test-ge, $(pahole-ver), 126) = -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs,global_var > > ifneq ($(KBUILD_EXTMOD),) > module-pahole-flags-$(call test-ge, $(pahole-ver), 126) += --btf_features=distilled_base > --------- > > With a suitable kernel config that has BTF enabled, you could then build like > so: > > PATH=path/to/pahole_build_dir make all > > And you'll be able to examine the size of the results with readelf, or dump the > results with bpftool. > > v2: https://lore.kernel.org/dwarves/20240920081903.13473-1-stephen.s.brennan@oracle.com/T/ > v1: https://lore.kernel.org/dwarves/20240912190827.230176-1-stephen.s.brennan@oracle.com/ > > Stephen Brennan (5): > btf_encoder: use bitfield to control var encoding > btf_encoder: stop indexing symbols for VARs > btf_encoder: explicitly check addr/size for u32 overflow > btf_encoder: allow encoding VARs from many sections > pahole: add global_var BTF feature > > btf_encoder.c | 348 +++++++++++++++++++++------------------------ > btf_encoder.h | 7 + > dwarves.h | 1 + > man-pages/pahole.1 | 7 +- > pahole.c | 3 +- > 5 files changed, 178 insertions(+), 188 deletions(-) > > -- > 2.43.5 > >
diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf index b75f09f3f424..c88d9e526426 100644 --- a/scripts/Makefile.btf +++ b/scripts/Makefile.btf @@ -19,7 +19,7 @@ pahole-flags-$(call test-ge, $(pahole-ver), 125) += --skip_encoding_btf_inconsis else # Switch to using --btf_features for v1.26 and later. -pahole-flags-$(call test-ge, $(pahole-ver), 126) = -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs +pahole-flags-$(call test-ge, $(pahole-ver), 126) = -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs,global_var ifneq ($(KBUILD_EXTMOD),) module-pahole-flags-$(call test-ge, $(pahole-ver), 126) += --btf_features=distilled_base
Hello all, This is v3 of the series to add global variables to pahole's generated BTF. Patches 1-3 of v2 were already merged. This series splits the last patch of v2 and does some small updates. It should apply cleanly to the "next" branch. https://github.com/acmel/dwarves/commits/btf_global_vars/ Changes since v2: 1. Split things out into several smaller patches as can be seen in the log below. 2. Previously the global_var feature was defined with BTF_DEFAULT_FEATURE, but I think we agreed in the discussion of v2 that it would be better as BTF_NON_DEFAULT_FEATURE, so I changed it to align with our discussion. 3. Removed the "--encode_btf_global_vars" option. 3. I went through and straightened out my use of integer types for ELF section index (size_t, as returned by libelf) as well as the variable addr and size. To this end I did add a few checks to explicitly ensure we don't overflow the uint32_t fields in the DATASEC. To test this out on a Linux build, you'll want to make the following change: --------- --------- With a suitable kernel config that has BTF enabled, you could then build like so: PATH=path/to/pahole_build_dir make all And you'll be able to examine the size of the results with readelf, or dump the results with bpftool. v2: https://lore.kernel.org/dwarves/20240920081903.13473-1-stephen.s.brennan@oracle.com/T/ v1: https://lore.kernel.org/dwarves/20240912190827.230176-1-stephen.s.brennan@oracle.com/ Stephen Brennan (5): btf_encoder: use bitfield to control var encoding btf_encoder: stop indexing symbols for VARs btf_encoder: explicitly check addr/size for u32 overflow btf_encoder: allow encoding VARs from many sections pahole: add global_var BTF feature btf_encoder.c | 348 +++++++++++++++++++++------------------------ btf_encoder.h | 7 + dwarves.h | 1 + man-pages/pahole.1 | 7 +- pahole.c | 3 +- 5 files changed, 178 insertions(+), 188 deletions(-)