Commit Graph

5 Commits

Author SHA1 Message Date
Barry Song 526940e396 scripts/gdb: add lx_current support for arm64
arm64 uses SP_EL0 to save the current task_struct address.  While running
in EL0, SP_EL0 is clobbered by userspace.  So if the upper bit is not 1
(not TTBR1), the current address is invalid.  This patch checks the upper
bit of SP_EL0, if the upper bit is 1, lx_current() of arm64 will return
the derefrence of current task.  Otherwise, lx_current() will tell users
they are running in userspace(EL0).

While arm64 is running in EL0, it is actually pointless to print current
task as the memory of kernel space is not accessible in EL0.

Link: https://lkml.kernel.org/r/20210314203444.15188-3-song.bao.hua@hisilicon.com
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kieran Bingham <kbingham@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-05-07 00:26:33 -07:00
Barry Song dc9586823f scripts/gdb: document lx_current is only supported by x86
Patch series "scripts/gdb: clarify the platforms supporting lx_current and add arm64 support", v2.

lx_current depends on per_cpu current_task variable which exists on x86
only.  so it actually works on x86 only.  the 1st patch documents this
clearly; the 2nd patch adds support for arm64.

This patch (of 2):

x86 is the only architecture which has per_cpu current_task:

  arch$ git grep current_task | grep -i per_cpu
  x86/include/asm/current.h:DECLARE_PER_CPU(struct task_struct *, current_task);
  x86/kernel/cpu/common.c:DEFINE_PER_CPU(struct task_struct *, current_task) ____cacheline_aligned =
  x86/kernel/cpu/common.c:EXPORT_PER_CPU_SYMBOL(current_task);
  x86/kernel/cpu/common.c:DEFINE_PER_CPU(struct task_struct *, current_task) = &init_task;
  x86/kernel/cpu/common.c:EXPORT_PER_CPU_SYMBOL(current_task);
  x86/kernel/smpboot.c:	per_cpu(current_task, cpu) = idle;

On other architectures, lx_current() will lead to a python exception:

  (gdb) p $lx_current().pid
  Python Exception <class 'gdb.error'> No symbol "current_task" in current context.:
  Error occurred in Python: No symbol "current_task" in current context.

To avoid more people struggling and wasting time in other architectures,
document it.

Link: https://lkml.kernel.org/r/20210314203444.15188-1-song.bao.hua@hisilicon.com
Link: https://lkml.kernel.org/r/20210314203444.15188-2-song.bao.hua@hisilicon.com
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-05-07 00:26:33 -07:00
Alexander A. Klimov 93431e0607 Replace HTTP links with HTTPS ones: documentation
Rationale:
Reduces attack surface on kernel devs opening the links for MITM
as HTTPS traffic is much harder to manipulate.

Deterministic algorithm:
For each file:
  For each line:
    If doesn't contain `\bxmlns\b`:
      For each link, `\bhttp://[^# \t\r\n]*(?:\w|/)`:
        If both the HTTP and HTTPS versions
        return 200 OK and serve the same content:
          Replace HTTP with HTTPS.

Signed-off-by: Alexander A. Klimov <grandmaster@al2klimov.de>
Link: https://lore.kernel.org/r/20200526060544.25127-1-grandmaster@al2klimov.de
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2020-06-08 09:30:19 -06:00
Zhouyi Zhou e604f1cb85 docs: disable KASLR when debugging kernel
commit 6807c84652 ("x86: Enable KASLR by default") enables KASLR
by default on x86. While KASLR will confuse gdb which resolve kernel
symbol address from symbol table of vmlinux. We should turn off KASLR for
kernel debugging.

Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
Reviewed-by: Kieran Bingham <kbingham@kernel.org>
Acked-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2017-07-17 14:49:01 -06:00
Jonathan Corbet 5f0962748d docs: Sphinxify gdb-kernel-debugging.txt and move to dev-tools
Acked-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2016-08-18 17:43:24 -06:00