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Changes have been made to recent versions of the Linux kernel to allow gdb to examine and modify the FPU contents.
The first changes occured in the 2.0.xx series kernels (first in 2.0.32). These were authored by Ramon Garcia Fernandez (firstname.lastname@example.org).
After seeing the approach used by Ramon, I decided that I preferred a modified approach and wrote some patches for the 2.1.xx series kernels. These patches appeared in the 2.1.73 kernel. If you want to use a kernel earlier than 2.1.73, you can get a copy of patches, which are against the 2.1.71 kernel here.
To make gdb recognise the new 2.1.xx kernel interface you will need to patch the gdb-4.16 or gdb-4.16 sources and compile a new gdb executable. You can get those patches here:
The gdb patches should be regarded as BETA software. Look for the file README.wm; if it exists it contains notes on usage.