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lx-dmesg needs access to the log_buf symbol from printk.c. Unfortunately, the symbol log_buf also exists in BPF's verifier.c and hence gdb can pick one or the other. If it happens to pick BPF's log_buf, lx-dmesg doesn't work: (gdb) lx-dmesg Python Exception <class 'gdb.MemoryError'> Cannot access memory at address 0x0: Error occurred in Python command: Cannot access memory at address 0x0 (gdb) p log_buf $15 = 0x0 Luckily, GDB has a way to deal with this, see https://sourceware.org/gdb/onlinedocs/gdb/Symbols.html (gdb) info variables ^log_buf$ All variables matching regular expression "^log_buf$": File <linux.git>/kernel/bpf/verifier.c: static char *log_buf; File <linux.git>/kernel/printk/printk.c: static char *log_buf; (gdb) p 'verifier.c'::log_buf $1 = 0x0 (gdb) p 'printk.c'::log_buf $2 = 0x811a6aa0 <__log_buf> "" (gdb) p &log_buf $3 = (char **) 0x8120fe40 <log_buf> (gdb) p &'verifier.c'::log_buf $4 = (char **) 0x8120fe40 <log_buf> (gdb) p &'printk.c'::log_buf $5 = (char **) 0x8048b7d0 <log_buf> By being explicit about the location of the symbol, we can make lx-dmesg work again. While at it, do the same for the other symbols we need from printk.c Link: http://lkml.kernel.org/r/20170526112222.3414-1-git@andred.net Signed-off-by: André Draszik <git@andred.net> Tested-by: Kieran Bingham <kieran@bingham.xyz> Acked-by: Jan Kiszka <jan.kiszka@siemens.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.