An issue has been found with current implementation of ARC signal restorer

function in uClibc and how GDB handles it. When debugger information is not

present, everything worked fine, because GDB would use a built-in logic to

determine if function is a signal restorer. However when debugging information

is present, debugger would rely solely on it and wouldn't use ARC-specific

functions to detect signal handler frames. Because debug information for signal restorer is generated

completely by the compiler, it lacks a marker, that identifies this as a

signal frame that requires special handling. While it is possible to insert

that marker via inline assembly, that still doesn't solve the whole problem,

because some other expectations are not met by the debug information - there

is no "nop" in front of the function, needed to fool debugger into thinking

that this was a function call, and references to previous frame information

need to be described manually. The simplest way to fix the problem is just

to make sure that signal restorer function will not have any debug function

at all, which can be done by writing it in assembly.

Alternative, more complex solution, where debug information for signal

frame is manually defined can be found in

glibc/sysdeps/unix/sysv/linux/x86_64/sigaction.c [1].

[1] https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/x86_64/sigaction.c;hb=HEAD

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>

Anton