DCE/DSE: Add Dead Syscalls Elimination support, part1

Hi, all

This series aims to add DCE based DSE support, here is the first revision of the RFC patchset [1], the whole series includes three parts, here is the Part1.

This Part1 adds basic DCE based DSE support.

Part2 will further eliminate the unused syscalls forcely kept by the exception tables.

Part3 will add DSE test support with nolibc-test.c.

Changes from RFC patchset [1]:

- The DCE support [2] for RISC-V has been merged [3]
- The "nolibc: Record used syscalls in their own sections" [4] will be delayed to Part3

- Add debug support for DCE
- Further allows CONFIG_USED_SYSCALLS accept a file stores used syscalls
- Now, only accepts symbolic syscalls, not support integral number again
- Works with newly added riscv syscalls suffix: __riscv_
- Further trims the syscall tables by removing the tailing invalid parts

The nolibc-test based initrd run well on riscv64 kernel image with dead syscalls eliminated:

    $ nm build/riscv64/virt/linux/v6.6-rc2/vmlinux | grep "T __riscv_sys" | grep -v sys_ni_syscall | wc -l
    48

These options should be enabled:

CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y
CONFIG_LD_DEAD_CODE_DATA_ELIMINATION_DEBUG=y
CONFIG_TRIM_UNUSED_SYSCALLS=y
CONFIG_USED_SYSCALLS="sys_dup sys_dup3 sys_ioctl sys_mknodat sys_mkdirat sys_unlinkat sys_symlinkat sys_linkat sys_mount sys_chdir sys_chroot sys_fchmodat sys_fchownat sys_openat sys_close sys_pipe2 sys_getdents64 sys_lseek sys_read sys_write sys_pselect6 sys_ppoll sys_exit sys_sched_yield sys_kill sys_reboot sys_getpgid sys_prctl sys_gettimeofday sys_getpid sys_getppid sys_getuid sys_geteuid sys_brk sys_munmap sys_clone sys_execve sys_mmap sys_wait4 sys_statx"

The really used syscalls:

    $ echo "sys_dup sys_dup3 sys_ioctl sys_mknodat sys_mkdirat sys_unlinkat sys_symlinkat sys_linkat sys_mount sys_chdir sys_chroot sys_fchmodat sys_fchownat sys_openat sys_close sys_pipe2 sys_getdents64 sys_lseek sys_read sys_write sys_pselect6 sys_ppoll sys_exit sys_sched_yield sys_kill sys_reboot sys_getpgid sys_prctl sys_gettimeofday sys_getpid sys_getppid sys_getuid sys_geteuid sys_brk sys_munmap sys_clone sys_execve sys_mmap sys_wait4 sys_statx" | tr ' ' '\n' | wc -l
    40

Thanks to Yuan Tan, he has researched and verified the elimination of the unused syscalls forcely kept by the exception tables, both section group and section link order attributes of ld work. part2 will be sent out soon to further remove another 8 unused syscalls and eventually we are able to run a dead loop application on a kernel image without syscalls.

Best Regards,
Zhangjin Wu

---
[1]: https://lore.kernel.org/lkml/[email protected]/
[2]: https://lore.kernel.org/lkml/234017be6d06ef84844583230542e31068fa3685.1676594211.git.falcon@tinylab.org/
[3]: https://lore.kernel.org/lkml/CAFP8O3+41QFVyNTVJ2iZYkB0tqnvdLTAoGShgGy-qPP1PHjBEw@mail.gmail.com/
[4]: https://lore.kernel.org/lkml/cbcbfbb37cabfd9aed6088c75515e4ea86006cff.1676594211.git.falcon@tinylab.org/

Zhangjin Wu (7):
DCE: add debug support
DCE/DSE: add unused syscalls elimination configure support DCE/DSE: Add a new scripts/Makefile.syscalls DCE/DSE: mips: add HAVE_TRIM_UNUSED_SYSCALLS support DCE/DSE: riscv: move syscall tables to syscalls/ DCE/DSE: riscv: add HAVE_TRIM_UNUSED_SYSCALLS support DCE/DSE: riscv: trim syscall tables

 Makefile                                      |  3 +
 arch/mips/Kconfig                             |  1 +
 arch/mips/kernel/syscalls/Makefile            | 23 ++++++-
 arch/riscv/Kconfig                            |  1 +
 arch/riscv/include/asm/unistd.h               |  2 +
 arch/riscv/kernel/Makefile                    |  7 +-
 arch/riscv/kernel/syscalls/Makefile           | 69 +++++++++++++++++++
 .../{ => syscalls}/compat_syscall_table.c     |  4 +-
 .../kernel/{ => syscalls}/syscall_table.c     |  4 +-
 init/Kconfig                                  | 49 +++++++++++++
 scripts/Makefile.syscalls                     | 29 ++++++++
 11 files changed, 182 insertions(+), 10 deletions(-)
 create mode 100644 arch/riscv/kernel/syscalls/Makefile
 rename arch/riscv/kernel/{ => syscalls}/compat_syscall_table.c (82%)
 rename arch/riscv/kernel/{ => syscalls}/syscall_table.c (83%)
 create mode 100644 scripts/Makefile.syscalls

2.25.1