How to debug/display Thumb instructions on GDB of Android NDK?

[Samuel]

Hello,

I use gdb's "x" command, for example:

   x/20i *0xb0006800

It displays wrong ARM instructions, because the data of this memory area are Thumb instructions.

But I can't display Thumb instructions on NDK GDB, how to enable Thumb instructions debug on Android NDK GDB?

Sam

[Mārtiņš Možeiko]

Have you tried looking in GDB manual?
http://sourceware.org/gdb/current/onlinedocs/gdb/ARM.html

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Mārtiņš Možeiko

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[Samuel]

Daer Mārtiņš Možeiko,

Thank you for your reply.

Did Sourceware's GDB can connect the GDB Server which prebuilt and provided by Android NDK?

Sam

On Tuesday, May 22, 2012 11:24:41 AM UTC+8, Mārtiņš Možeiko wrote:

Have you tried looking in GDB manual?
http://sourceware.org/gdb/current/onlinedocs/gdb/ARM.html

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Mārtiņš Možeiko


On Mon, May 21, 2012 at 7:34 PM, Samuel <s...@samuel.pro> wrote:
> Hello,
>
> I use gdb's "x" command, for example:
>
>    x/20i *0xb0006800
>
> It displays wrong ARM instructions, because the data of this memory area are
> Thumb instructions.
>
> But I can't display Thumb instructions on NDK GDB, how to enable
> Thumb instructions debug on Android NDK GDB?
>
> Sam
>
> --
> You received this message because you are subscribed to the Google Groups
> "android-ndk" group.
> To view this discussion on the web visit
> https://groups.google.com/d/msg/android-ndk/-/rhKGPooHtVwJ.
> To post to this group, send email to andro...@googlegroups.com.
> To unsubscribe from this group, send email to

> android-ndk+unsubscribe@googlegroups.com.

[David Turner]

On ARM, the low order bit of an function address is used to determine if the corresponding code is 32-bit ARM (set to 0), or 16-bit Thumb (set to 1).

In other words:

  x/20i *0xb0006800    -> will display 20 32-bit ARM instructions starting at address 0xb0006800

  x/20i *0xb0006801    -> will display 20 16-bit Thumb instructions starting at address 0xb0006800

Only the lower bit value changes.

I'm surprised this isn't in the ARM-specific portion of the GDB manual.

Hope this helps

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[Mārtiņš Možeiko]

"Sourceware's GDB" is THE gdb It is homepage of GDB. Android uses GDB,
so manual from "Sourceware" works for any GDB. There is nothing
special needed to connect with something.

--
Martins Mozeiko

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>

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Mārtiņš Možeiko

[邓尧]

I built my own gdb-7.4. then set fallback mode with command:
    set arm fallback-mode thumb
It seems that the gdb provided by android-ndk doesn't support this command. Personally, I prefer "disassemble" command to check instructions:
    disassemble 0xb0006800,+40

Thanks
Yao

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