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docs: disable KASLR when debugging kernel

PATCH In review Zhouyi Zhou 3 participants 3 messages Jul 7, 2017 – Jul 13, 2017

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Zhouyi Zhou

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PATCH v2 2/2 docs: disable KASLR when debugging kernel

commit 6807c84652b0 ("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 <[email protected]>
Reviewed-by Kieran Bingham <[email protected]>
---
 Documentation/dev-tools/gdb-kernel-debugging.rst | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
Documentation/dev-tools/gdb-kernel-debugging.rst +4 -2
index 5e93c9b..60fec6d 100644
@@ -31,12 +31,13 @@ Setup
   CONFIG_DEBUG_INFO_REDUCED off. If your architecture supports
   CONFIG_FRAME_POINTER, keep it enabled.
 
-- Install that kernel on the guest.
+- Install that kernel on the guest, turn off KASLR if necessary by adding
+  "nokaslr" to the kernel command line.
   Alternatively, QEMU allows to boot the kernel directly using -kernel,
   -append, -initrd command line switches. This is generally only useful if
   you do not depend on modules. See QEMU documentation for more details on
-  this mode.
+  this mode. In this case, you should build the kernel with
+  CONFIG_RANDOMIZE_BASE disabled if the architecture supports KASLR.
 
 - Enable the gdb stub of QEMU/KVM, either
Signature · 1 line
1.9.1
#1 lore raw
Quoted 22 lines · Zhouyi Zhou

commit 6807c84652b0 ("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 <[email protected]>
Reviewed-by Kieran Bingham <[email protected]>
---
 Documentation/dev-tools/gdb-kernel-debugging.rst | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
Documentation/dev-tools/gdb-kernel-debugging.rst +1 -1
index 5e93c9b..60fec6d 100644
@@ -31,12 +31,13 @@ Setup
   CONFIG_DEBUG_INFO_REDUCED off. If your architecture supports
   CONFIG_FRAME_POINTER, keep it enabled.
 
-- Install that kernel on the guest.
+- Install that kernel on the guest, turn off KASLR if necessary by adding

Documentation/dev-tools/gdb-kernel-debugging.rst Setup · line 43

Quoted 10 lines
Documentation/dev-tools/gdb-kernel-debugging.rst +3 -1
+  "nokaslr" to the kernel command line.
   Alternatively, QEMU allows to boot the kernel directly using -kernel,
   -append, -initrd command line switches. This is generally only useful if
   you do not depend on modules. See QEMU documentation for more details on
-  this mode.
+  this mode. In this case, you should build the kernel with
+  CONFIG_RANDOMIZE_BASE disabled if the architecture supports KASLR.
 
 - Enable the gdb stub of QEMU/KVM, either

FWIW: Acked-by: Jan Kiszka <[email protected]>

Who's taking this? Jon?

Jan

Signature · 2 lines
Siemens AG, Corporate Technology, CT RDA ITP SES-DE
Corporate Competence Center Embedded Linux