[Bug libdw/28579] New: libdwfl api for accessing registers for a thread frame (full register unwinding)

[Bug libdw/28579] New: libdwfl api for accessing registers for a thread frame (full register unwinding)

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28579

            Bug ID: 28579
           Summary: libdwfl api for accessing registers for a thread frame
                    (full register unwinding)
           Product: elfutils
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libdw
          Assignee: unassigned at sourceware dot org
          Reporter: mark at klomp dot org
                CC: elfutils-devel at sourceware dot org
  Target Milestone: ---

dwfl has most of the infrastructure to keep the full unwind state, including
the state of unwound registers per frame using Dwfl_Thread_Callbacks. But there
is no public API to access that state, except for the PC (dwfl_frame_pc).

There should be other methods on Dwfl_Frame to access other state.

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[Bug libdw/28579] libdwfl api for accessing registers for a thread frame (full register unwinding)

[dichen at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28579

Di Chen <dichen at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dichen at redhat dot com
           Assignee|unassigned at sourceware dot org   |dichen at redhat dot com

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[Bug libdw/28579] libdwfl api for accessing registers for a thread frame (full register unwinding)

[dichen at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28579

Di Chen <dichen at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

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[Bug libdw/28579] libdwfl api for accessing registers for a thread frame (full register unwinding)

[dichen at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28579

--- Comment #1 from Di Chen <dichen at redhat dot com> ---
Created attachment 14193
  --> https://sourceware.org/bugzilla/attachment.cgi?id=14193&action=edit
Submit a Patch for Bug 28579

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[Bug libdw/28579] libdwfl api for accessing registers for a thread frame (full register unwinding)

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28579

--- Comment #2 from Mark Wielaard <mark at klomp dot org> ---
Thanks. This looks nice and simple. Few small comments:

- The dwfl_frame_reg should be in a new ELFUTILS_0.188 { global:
dwfl_frame_reg; } ELFUTILS_0.186; section (that is, this symbol is new in
ELFUTILS_0.188 which inherits from ELFUTILS_0.186).

- Technically __libdwfl_frame_reg_get failing can be either invalid register or
unknown value (if state->regs_set is false). It might make sense to set a
different error message if it isn't too much work.

- When using public functions internally we usually use INTUSE
(dwfl_frame_reg). Which is an tiny optimization to avoid a plt call. You'll
need an INTDECL in libdwflP.h.

- In the unwinder we are only really interested in addresses, which is why we
use Dwarf_Addr, but here I think we should use Dwarf_Word as the *val that
dwfl_frame_reg returns. Both are really uint64_t, so it doesn't really matter,
but it makes it more clear that the caller is responsible for interpreting the
register value.

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[Bug libdw/28579] libdwfl api for accessing registers for a thread frame (full register unwinding)

[dichen at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28579

--- Comment #3 from Di Chen <dichen at redhat dot com> ---
Thank you Mark,

I have re-pushed a patch[1] for

1). add dwfl_frame_reg to ELFUTILS_0.188
2). add invalid regno check for dwfl_frame_reg
3). add INTDECL (dwfl_frame_reg)
4). Replace Dwarf_Word with Dwarf_Addr for *val

[1] https://sourceware.org/pipermail/elfutils-devel/2022q3/005206.html

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