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When MD_FALLBACK_FRAME_STATE_FOR handler in libgcc unwind code checks
the second instruction opcode in __default_rt_sa_restorer function,
it expects to see the following values for ARC cores:
- 0x7ee0781e for ARCv2 LE
- 0x003f226f for ARC700 LE
ARC700 value correspond to trap0 instruction. ARCv2 value corresponds
to the following code:
traps_0
j_s [blink]
However, unlike glibc, uClibc implementation of __default_rt_sa_restorer
for ARC does not have that jump. Hence libgcc unwind code is not able
to recognize signal frame correctly on ARCv2 and completes too early.
This change fixes libgcc unwinding over signal frame on ARCv2 adding
missing jump to __default_rt_sa_restorer.
Signed-off-by: Sergey Matyukevich <sergey.matyukevich@synopsys.com>
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An issue has been found with current implementation of 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>
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Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
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For this port, I would like to give due credit to:
- Folks from Codito technologies (Sameer, Amit, Kanika, Ramana,...)
who did the very first port
- ARC UK from 2007-2009 (Joern, Irfan, Khurram, Phil...
- Late Brendan Kehoe (may he RIP)
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
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