[v3: https://gcc.gnu.org/pipermail/gcc-patches/2024-May/653165.html Changes from v3: - Address typos, comment fixes and other minor nits pointed out by Indu in patches 1-3 and 5. - Rename option added in patch 4 from -fprune-btf to -gprune-btf. - Reword commit message in patch 4 to better describe behavior of -gprune-btf between LTO and non-LTO builds. - Improve the option parsing in patch 6 using Indu's suggested approach. Add a few tests for -gdwarf, -gbtf, -gctf interaction. ]
Review status: - Patches 1-3 have been approved, not yet pushed. - The CTF/BTF portion of patch 5 has been approved; the remaining portion needs BPF backend reviewer approval. - Patches 4 and 6 need review. Both have portions which I think need global maintainer approval. ] This patch series signficantly refactors the BTF generation in gcc, making it simpler and easier to understand, extend and maintain. It also introduces an optional algorithm to "prune" BTF information before emission. This pruning is meant to be used for BPF programs, to alleviate the massive bloating of BTF information caused by including Linux kernel internal headers. The pruning is designed to be compatible with the unconditional pruning performed by the LLVM BPF backend when generating BTF information. While the changes are fairly significant, there is no actual change in emitted BTF information (unless pruning is enabled), other than bug fixes and small additions to the assembler debug comments. Patch 1 restructures the emission of CTF and BTF information, with the result that CTF is always completely generated and emitted before any BTF-related procedures are run. BTF emission is moved to late finish for all targets, except when building with -flto. Patch 2 changes the data structures shared by CTF and BTF to use pointers rather than type IDs for all inter-type references. This change is completely transparent to both CTF and BTF. Patch 3 heavily refactors btfout.cc to take advantage of the prior changes and significantly simplify the BTF implementation. The changes are nearly transparent, however some small but important improvements are also made possible by the refactor, such as fixing PR113566 for non-LTO builds. Patch 4 adds a new option to perform pruning of the BTF information before emission. This is intended to be used for BPF programs which often include kernel headers, and in many cases reduces the size of the resulting BTF information by a factor of 10. Patch 5 makes BTF pruning work with BPF CO-RE, and enables the pruning by default in the BPF backend. Patch 6 takes advantage of the prior changes, and removes the restriction on generating both CTF and BTF in the same compiler run, allowing for any combinaion of -gdwarf, -gctf and -gbtf. Tested on x86_64-linux-gnu, and on x86_64-linux-gnu host for bpf-unknown-none target. Also tested by compiling and runninng Linux kernel BPF selftests. No known regressions. David Faust (6): ctf, btf: restructure CTF/BTF emission ctf: use pointers instead of IDs internally btf: refactor and simplify implementation btf: add -gprune-btf option bpf,btf: enable BTF pruning by default for BPF opts: allow any combination of DWARF, CTF, BTF gcc/btfout.cc | 1615 +++++++++-------- gcc/common.opt | 4 + gcc/config/bpf/bpf.cc | 5 + gcc/config/bpf/btfext-out.cc | 14 +- gcc/config/bpf/core-builtins.cc | 74 +- gcc/ctfc.cc | 153 +- gcc/ctfc.h | 113 +- gcc/ctfout.cc | 22 +- gcc/doc/invoke.texi | 23 + gcc/dwarf2ctf.cc | 324 ++-- gcc/dwarf2ctf.h | 2 +- gcc/dwarf2out.cc | 4 +- gcc/opts.cc | 20 +- gcc/testsuite/gcc.dg/debug/btf/btf-3.c | 8 + gcc/testsuite/gcc.dg/debug/btf/btf-4.c | 8 + gcc/testsuite/gcc.dg/debug/btf/btf-5.c | 9 + gcc/testsuite/gcc.dg/debug/btf/btf-prune-1.c | 25 + gcc/testsuite/gcc.dg/debug/btf/btf-prune-2.c | 33 + gcc/testsuite/gcc.dg/debug/btf/btf-prune-3.c | 35 + .../gcc.dg/debug/btf/btf-prune-maps.c | 20 + .../gcc.dg/debug/btf/btf-variables-5.c | 6 +- include/btf.h | 5 + 22 files changed, 1457 insertions(+), 1065 deletions(-) create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-3.c create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-4.c create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-5.c create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-prune-1.c create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-prune-2.c create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-prune-3.c create mode 100644 gcc/testsuite/gcc.dg/debug/btf/btf-prune-maps.c -- 2.43.0
