On Mon, Feb 10, 2025 at 12:30 AM Weinan Liu <wn...@google.com> wrote: > I already have a WIP patch to add sframe support to the kernel module. > However, it is not yet working. I had trouble unwinding frames for the > kernel module using the current algorithm. > > Indu has likely identified the issue and will be addressing it from the > toolchain side. > > https://sourceware.org/bugzilla/show_bug.cgi?id=32666
I have a working in progress patch that adds sframe support for kernel module. https://github.com/heuza/linux/tree/sframe_unwinder.rfc According to the sframe table values I got during runtime testing, looks like the offsets are not correct . When unwind symbols init_module(0xffff80007b155048) from the kernel module(livepatch-sample.ko), the start_address of the FDE entries in the sframe table of the kernel modules appear incorrect. For instance, the first FDE's start_addr is reported as -20564. Adding this offset to the module's sframe section address (0xffff80007b15a040) yields 0xffff80007b154fec, which is not within the livepatch-sample.ko memory region(It should be larger than 0xffff80007b155000). Here are the sframe table values of the livepatch-samples.ko that I print by qemu + gdb. ``` $ /usr/bin/aarch64-linux-gnu-objdump -L --sframe=.sframe ./samples/livepatch/livepatch-sample.ko ./samples/livepatch/livepatch-sample.ko: file format elf64-littleaarch64 Contents of the SFrame section .sframe: Header : Version: SFRAME_VERSION_2 Flags: SFRAME_F_FDE_SORTED Num FDEs: 3 Num FREs: 11 Function Index : func idx [0]: pc = 0x0, size = 12 bytes STARTPC CFA FP RA 0000000000000000 sp+0 u u func idx [1]: pc = 0x0, size = 44 bytes STARTPC CFA FP RA 0000000000000000 sp+0 u u 000000000000000c sp+0 u u[s] 0000000000000010 sp+16 c-16 c-8[s] 0000000000000024 sp+0 u u[s] 0000000000000028 sp+0 u u func idx [2]: pc = 0x0, size = 56 bytes STARTPC CFA FP RA 0000000000000000 sp+0 u u 000000000000000c sp+0 u u[s] 0000000000000010 sp+16 c-16 c-8[s] 0000000000000030 sp+0 u u[s] 0000000000000034 sp+0 u u (gdb) bt #0 find_fde (tbl=0xffff80007b157708, pc=18446603338286190664) at kernel/sframe_lookup.c:75 #1 0xffff80008031e260 in sframe_find_pc (pc=18446603338286190664, entry=0xffff800086f83800) at kernel/sframe_lookup.c:175 #2 0xffff800080035a48 in unwind_next_frame_sframe (state=0xffff800086f83828) at arch/arm64/kernel/stacktrace.c:270 #3 kunwind_next (state=0xffff800086f83828) at arch/arm64/kernel/stacktrace.c:332 ... (gdb) lx-symbols loading vmlinux scanning for modules in /home/wnliu/kernel loading @0xffff80007b155000: /home/wnliu/kernel/samples/livepatch/livepatch-sample.ko loading @0xffff80007b14d000: /home/wnliu/kernel/fs/fat/vfat.ko loading @0xffff80007b130000: /home/wnliu/kernel/fs/fat/fat.ko (gdb) p/x *tbl->sfhdr_p $5 = {preamble = {magic = 0xdee2, version = 0x2, flags = 0x1}, abi_arch = 0x2, cfa_fixed_fp_offset = 0x0, cfa_fixed_ra_offset = 0x0, auxhdr_len = 0x0, num_fdes = 0x3, num_fres = 0xb, fre_len = 0x25, fdes_off = 0x0, fres_off = 0x3c} (gdb) p/x tbl->sfhdr_p $6 = 0xffff80007b15a040 (gdb) p *tbl->fde_p $7 = {start_addr = -20564, size = 12, fres_off = 0, fres_num = 1, info = 0 '\000', rep_size = 0 '\000', padding = 0} (gdb) p *(tbl->fde_p + 1) $11 = {start_addr = -20552, size = 44, fres_off = 3, fres_num = 5, info = 0 '\000', rep_size = 0 '\000', padding = 0} (gdb) p *(tbl->fde_p + 2) $12 = {start_addr = -20508, size = 56, fres_off = 20, fres_num = 5, info = 0 '\000', rep_size = 0 '\000', padding = 0} /* -20564 + 0xffff80007b15a040 = 0xffff80007b154fec */ (gdb) info symbol 0xffff80007b154fec No symbol matches 0xffff80007b154fec ```
