# git rev-parse -q --verify 6d65028eb67dbb7627651adfc460d64196d38bd8^{commit} 6d65028eb67dbb7627651adfc460d64196d38bd8 already have revision, skipping fetch # git checkout -q -f -B kisskb 6d65028eb67dbb7627651adfc460d64196d38bd8 # git clean -qxdf # < git log -1 # commit 6d65028eb67dbb7627651adfc460d64196d38bd8 # Author: Michael Ellerman # Date: Mon May 2 22:50:10 2022 +1000 # # powerpc/vdso: Fix incorrect CFI in gettimeofday.S # # As reported by Alan, the CFI (Call Frame Information) in the VDSO time # routines is incorrect since commit ce7d8056e38b ("powerpc/vdso: Prepare # for switching VDSO to generic C implementation."). # # DWARF has a concept called the CFA (Canonical Frame Address), which on # powerpc is calculated as an offset from the stack pointer (r1). That # means when the stack pointer is changed there must be a corresponding # CFI directive to update the calculation of the CFA. # # The current code is missing those directives for the changes to r1, # which prevents gdb from being able to generate a backtrace from inside # VDSO functions, eg: # # Breakpoint 1, 0x00007ffff7f804dc in __kernel_clock_gettime () # (gdb) bt # #0 0x00007ffff7f804dc in __kernel_clock_gettime () # #1 0x00007ffff7d8872c in clock_gettime@@GLIBC_2.17 () from /lib64/libc.so.6 # #2 0x00007fffffffd960 in ?? () # #3 0x00007ffff7d8872c in clock_gettime@@GLIBC_2.17 () from /lib64/libc.so.6 # Backtrace stopped: frame did not save the PC # # Alan helpfully describes some rules for correctly maintaining the CFI information: # # 1) Every adjustment to the current frame address reg (ie. r1) must be # described, and exactly at the instruction where r1 changes. Why? # Because stack unwinding might want to access previous frames. # # 2) If a function changes LR or any non-volatile register, the save # location for those regs must be given. The CFI can be at any # instruction after the saves up to the point that the reg is # changed. # (Exception: LR save should be described before a bl. not after) # # 3) If asychronous unwind info is needed then restores of LR and # non-volatile regs must also be described. The CFI can be at any # instruction after the reg is restored up to the point where the # save location is (potentially) trashed. # # Fix the inability to backtrace by adding CFI directives describing the # changes to r1, ie. satisfying rule 1. # # Also change the information for LR to point to the copy saved on the # stack, not the value in r0 that will be overwritten by the function # call. # # Finally, add CFI directives describing the save/restore of r2. # # With the fix gdb can correctly back trace and navigate up and down the stack: # # Breakpoint 1, 0x00007ffff7f804dc in __kernel_clock_gettime () # (gdb) bt # #0 0x00007ffff7f804dc in __kernel_clock_gettime () # #1 0x00007ffff7d8872c in clock_gettime@@GLIBC_2.17 () from /lib64/libc.so.6 # #2 0x0000000100015b60 in gettime () # #3 0x000000010000c8bc in print_long_format () # #4 0x000000010000d180 in print_current_files () # #5 0x00000001000054ac in main () # (gdb) up # #1 0x00007ffff7d8872c in clock_gettime@@GLIBC_2.17 () from /lib64/libc.so.6 # (gdb) # #2 0x0000000100015b60 in gettime () # (gdb) # #3 0x000000010000c8bc in print_long_format () # (gdb) # #4 0x000000010000d180 in print_current_files () # (gdb) # #5 0x00000001000054ac in main () # (gdb) # Initial frame selected; you cannot go up. # (gdb) down # #4 0x000000010000d180 in print_current_files () # (gdb) # #3 0x000000010000c8bc in print_long_format () # (gdb) # #2 0x0000000100015b60 in gettime () # (gdb) # #1 0x00007ffff7d8872c in clock_gettime@@GLIBC_2.17 () from /lib64/libc.so.6 # (gdb) # #0 0x00007ffff7f804dc in __kernel_clock_gettime () # (gdb) # # Fixes: ce7d8056e38b ("powerpc/vdso: Prepare for switching VDSO to generic C implementation.") # Cc: stable@vger.kernel.org # v5.11+ # Reported-by: Alan Modra # Signed-off-by: Michael Ellerman # Reviewed-by: Segher Boessenkool # Link: https://lore.kernel.org/r/20220502125010.1319370-1-mpe@ellerman.id.au # < /opt/cross/kisskb/korg/gcc-9.4.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-9.4.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version # < git log --format=%s --max-count=1 6d65028eb67dbb7627651adfc460d64196d38bd8 # < make -s -j 120 ARCH=powerpc O=/kisskb/build/powerpc-fixes_powernv_defconfig+STRICT_RWX_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.4.0-nolibc/powerpc64-linux/bin/powerpc64-linux- powernv_defconfig # Added to kconfig CONFIG_RELOCATABLE=n # Added to kconfig CONFIG_STRICT_KERNEL_RWX=y # < make -s -j 120 ARCH=powerpc O=/kisskb/build/powerpc-fixes_powernv_defconfig+STRICT_RWX_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.4.0-nolibc/powerpc64-linux/bin/powerpc64-linux- help # make -s -j 120 ARCH=powerpc O=/kisskb/build/powerpc-fixes_powernv_defconfig+STRICT_RWX_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.4.0-nolibc/powerpc64-linux/bin/powerpc64-linux- olddefconfig .config:4109:warning: override: reassigning to symbol RELOCATABLE # make -s -j 120 ARCH=powerpc O=/kisskb/build/powerpc-fixes_powernv_defconfig+STRICT_RWX_powerpc-gcc9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-9.4.0-nolibc/powerpc64-linux/bin/powerpc64-linux- Completed OK # rm -rf /kisskb/build/powerpc-fixes_powernv_defconfig+STRICT_RWX_powerpc-gcc9 # Build took: 0:01:21.096432