On 2024-07-19 15:54, Matthieu Longo wrote:
This patch series is only a refactoring of the existing implementation of PAuth and returned-address signing. The existing behavior is preserved.1. aarch64: store signing key and signing method in DWARF _Unwind_FrameState _Unwind_FrameState already contains several CIE and FDE information (see the attributes below the comment "The information we care about from the CIE/FDE" in libgcc/unwind-dw2.h). The patch aims at moving the information from DWARF CIE (signing key stored in the augmentation string) and FDE (the used signing method) into _Unwind_FrameState along the already-stored CIE and FDE information. Note: those information have to be saved in frame_state_reg_info instead of _Unwind_FrameState as they need to be savable by DW_CFA_remember_state and restorable by DW_CFA_restore_state, that both rely on the attribute "prev". Those new information in _Unwind_FrameState simplifies the look-up of the signing key when the return address is demangled. It also allows future signing methods to be easily added. _Unwind_FrameState is not a part of the public API of libunwind, so the change is backward compatible. A new architecture-specific handler MD_ARCH_EXTENSION_FRAME_INIT allows to reset values in the frame state and unwind context if needed by the architecture extension before changing the frame state to the caller context. A new architecture-specific handler MD_ARCH_EXTENSION_CIE_AUG_HANDLER isolates the architecture-specific augmentation strings in AArch64 backend, and allows others architectures to reuse augmentation strings that would have clashed with AArch64 DWARF extensions. aarch64_demangle_return_addr, DW_CFA_AARCH64_negate_ra_state and DW_CFA_val_expression cases in libgcc/unwind-dw2-execute_cfa.h were documented to clarify where the value of the RA state register is stored (FS and CONTEXT respectively). 2. libgcc: hide CIE and FDE data for DWARF architecture extensions behind a handler. This patch provides a new handler MD_ARCH_FRAME_STATE_T to hide an architecture-specific structure containing CIE and FDE data related to DWARF architecture extensions. Hiding the architecture-specific attributes behind a handler has the following benefits: 1. isolating those data from the generic ones in _Unwind_FrameState 2. avoiding casts to custom types. 3. preserving typing information when debugging with GDB, and so facilitating their printing. This approach required to add a new header md-unwind-def.h included at the top of libgcc/unwind-dw2.h, and redirecting to the corresponding architecture header via a symbolic link. An obvious drawback is the increase in complexity with macros, and headers. It also caused a split of architecture definitions between md-unwind-def.h (types definitions used in unwind-dw2.h) and md-unwind.h (local types definitions and handlers implementations). The naming of md-unwind.h with .h extension is a bit misleading as the file is only included in the middle of unwind-dw2.c. Changing this naming would require modification of others backends, which I prefered to abstain from. Overall the benefits are worth the added complexity from my perspective. 3. libgcc: update configure (regenerated by autoreconf) Regenerate the build files. ## Testing Those changes were testing by covering the 3 following cases: - backtracing. - exception handling in a C++ program. - gcc/testsuite/gcc.target/aarch64/pr104689.c: pac-ret with unusual DWARF [1] Regression tested on aarch64-unknown-linux-gnu, and no regression found. [1]: https://gcc.gnu.org/pipermail/gcc-patches/2022-May/594414.html Ok for master? I don't have commit access so I need someone to commit on my behalf. Regards, Matthieu. Matthieu Longo (3): aarch64: store signing key and signing method in DWARF _Unwind_FrameState libgcc: hide CIE and FDE data for DWARF architecture extensions behind a handler. libgcc: update configure (regenerated by autoreconf) libgcc/Makefile.in | 6 +- libgcc/config.host | 13 +- libgcc/config/aarch64/aarch64-unwind-def.h | 41 ++++++ libgcc/config/aarch64/aarch64-unwind.h | 150 +++++++++++++++++---- libgcc/configure | 2 + libgcc/configure.ac | 1 + libgcc/unwind-dw2-execute_cfa.h | 34 +++-- libgcc/unwind-dw2.c | 19 ++- libgcc/unwind-dw2.h | 19 ++- 9 files changed, 233 insertions(+), 52 deletions(-) create mode 100644 libgcc/config/aarch64/aarch64-unwind-def.h
Adding Ian in CC as he is listed as the maintainer of libgcc in MAINTAINERS file.
