Since kernel version 4.19-rc5 (Commit 23c85094fe1895caefdd ["proc/kcore: add vmcoreinfo note to /proc/kcore"]), '/proc/kcore' contains a new PT_NOTE which carries the VMCOREINFO information. If the same is available, one should prefer the same to retrieve 'PHYS_OFFSET' value exported by the kernel as this is now the standard interface exposed by kernel for sharing machine specific details with the user-land as per the arm64 kernel maintainers (see [0]). Also on certain arm64 platforms, it has been noticed that due to a hole at the start of physical ram exposed to kernel (i.e. it doesn't start from address 0), the kernel still calculates the 'memstart_addr' kernel variable as 0. Whereas the SYSTEM_RAM or IOMEM_RESERVED range in '/proc/iomem' would carry a first entry whose start address is non-zero (as the physical ram exposed to the kernel starts from a non-zero address). In such cases, if we rely on '/proc/iomem' entries to calculate the phys_offset, then we will have mismatch between the user-space and kernel space 'PHYS_OFFSET' value. The present 'kexec-tools' code does the same in 'get_memory_ranges_iomem_cb()' function when it makes a call to 'set_phys_offset()'. This can cause the vmcore generated via 'kexec-tools' to miss the last few bytes as the first '/proc/iomem' starts from a non-zero address. Details about the patches in this series: ---------------------------------------- PATCH 1/2 -> - Tries to move the elf read functionality from 'vmcore-dmesg.c' to a new utility library named 'elf_info.c', so that subsequent patches can use the same. - See the patch log for more details. PATCH 2/2 -> - Implements the actual functionality of reading the PHYS_OFFSET for arm64 platforms from the vmcoreinfo inside '/proc/kcore' (if available). - See the patch log for more details. Testing: -------- I tested this patchset on qualcomm-amberwing and huawei-taishan arm64 boards for non-KALSR boot mode. Both display the same PHYS_OFFSET in user-space as the value used by kernel after this patch. I will send a separate followup patch to fix the KASLR boot cases (as the discussion on the same is in progress with the arm64 kernel maintainers). [0] https://www.mail-archive.com/kexec@xxxxxxxxxxxxxxxxxxx/msg20300.html Bhupesh Sharma (2): util_lib: Add functionality to read elf notes arm64: Add support to read PHYS_OFFSET from '/proc/kcore' (if available) kexec/arch/arm64/kexec-arm64.c | 73 ++ util_lib/Makefile | 4 +- vmcore-dmesg/vmcore-dmesg.c => util_lib/elf_info.c | 157 +++-- util_lib/include/elf_info.h | 30 + vmcore-dmesg/Makefile | 4 +- vmcore-dmesg/vmcore-dmesg.c | 742 +-------------------- 6 files changed, 219 insertions(+), 791 deletions(-) copy vmcore-dmesg/vmcore-dmesg.c => util_lib/elf_info.c (88%) create mode 100644 util_lib/include/elf_info.h -- 2.7.4 _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
