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 BPF progams caused by including Linux kernel internal headers. The pruning is designed to be almost equivalent to that performed unconditionally by the LLVM BPF backend when generating BTF information, for compatibility purposes. While the changes are fairly significant, there is very little actual change in emitted BTF information (unless pruning is enabled), other than bug fixes and 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. Patch 2 takes advantage of that change, and removes the restriction on generating both CTF and BTF in the same compiler run, allowing for any combinaion of -gdwarf, -gctf and -gbtf. Patch 3 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 4 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. Patch 5 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 6 makes BTF pruning work with BPF CO-RE, and enables the pruning by default in the BPF backend. Tested on x86_64-linux-gnu, and on x86_64-linux-gnu host for bpf-unknown-none target. Also heavily tested with Linux kernel BPF selftests. No known regressions. David Faust (6): ctf, btf: restructure CTF/BTF emission opts: allow any combination of DWARF, CTF, BTF ctf: use pointers instead of IDs internally btf: refactor and simplify implementation btf: add -fprune-btf option bpf,btf: enable BTF pruning by default for BPF gcc/btfout.cc | 1645 ++++++++++------- gcc/common.opt | 4 + gcc/config/bpf/bpf.cc | 5 + gcc/config/bpf/btfext-out.cc | 12 +- gcc/config/bpf/core-builtins.cc | 73 +- gcc/ctfc.cc | 139 +- gcc/ctfc.h | 86 +- gcc/ctfout.cc | 19 +- gcc/doc/invoke.texi | 23 + gcc/dwarf2ctf.cc | 300 ++- gcc/dwarf2ctf.h | 2 +- gcc/dwarf2out.cc | 4 +- gcc/opts.cc | 19 +- 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-variables-5.c | 2 +- 17 files changed, 1399 insertions(+), 1027 deletions(-) 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 -- 2.43.0
