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From: "craig.blackmore at embecosm dot com"
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Subject: [Bug gdb/29046] New: RISC-V: call fails with non-executable stack
Date: Mon, 11 Apr 2022 15:13:13 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D29046

            Bug ID: 29046
           Summary: RISC-V: call fails with non-executable stack
           Product: gdb
           Version: HEAD
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: craig.blackmore at embecosm dot com
  Target Milestone: ---

Doing `call <function>` on an inferior with a non-executable stack fails
because GDB sets the return address of `<function>` to a location on the st=
ack
on which a breakpoint is set. When <function> returns, jumping to this stack
location triggers an instruction access exception. I suspect other targets =
may
also have a similar issue.

I have three ideas for making this work:

1. Make `gdbarch_call_dummy_location` configurable so that `AT_ENTRY_POINT`
could be used optionally instead of `ON_STACK`, however, this may still cau=
se
issues for multi-thread targets
https://sourceware.org/bugzilla/show_bug.cgi?id=3D10944#c6.

2. Reinstate `AT_SYMBOL` (removed in
`2efbc0f7220afb483293e101e25bf2e93bce0787`), so that unlike `AT_ENTRY_POINT`
the return address could be somewhere that no other thread is expected to be
executing.

3. According to the RISC-V priv spec 20190608, hardware breakpoints have a
higher priority than instruction access faults. In the RISC-V backend,
optionally use a hardware breakpoint on the stack location. The drawback is
that there needs to be a hardware breakpoint available unlike option 2 (and
option 1 if the entry point is in writable memory).

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