gdb.info: Overlay Commands

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Overlay Commands

To use GDB's overlay support, each overlay in your program must
correspond to a separate section of the executable file.  The section's
virtual memory address and load memory address must be the overlay's
mapped and load addresses.  Identifying overlays with sections allows
GDB to determine the appropriate address of a function or variable,
depending on whether the overlay is mapped or not.
   GDB's overlay commands all start with the word `overlay'; you can
abbreviate this as `ov' or `ovly'.  The commands are:
`overlay off'
     Disable GDB's overlay support.  When overlay support is disabled,
     GDB assumes that all functions and variables are always present at
     their mapped addresses.  By default, GDB's overlay support is
     disabled.
`overlay manual'
     Enable "manual" overlay debugging.  In this mode, GDB relies on
     you to tell it which overlays are mapped, and which are not, using
     the `overlay map-overlay' and `overlay unmap-overlay' commands
     described below.
`overlay map-overlay OVERLAY'
`overlay map OVERLAY'
     Tell GDB that OVERLAY is now mapped; OVERLAY must be the name of
     the object file section containing the overlay.  When an overlay
     is mapped, GDB assumes it can find the overlay's functions and
     variables at their mapped addresses.  GDB assumes that any other
     overlays whose mapped ranges overlap that of OVERLAY are now
     unmapped.
`overlay unmap-overlay OVERLAY'
`overlay unmap OVERLAY'
     Tell GDB that OVERLAY is no longer mapped; OVERLAY must be the
     name of the object file section containing the overlay.  When an
     overlay is unmapped, GDB assumes it can find the overlay's
     functions and variables at their load addresses.
`overlay auto'
     Enable "automatic" overlay debugging.  In this mode, GDB consults
     a data structure the overlay manager maintains in the inferior to
     see which overlays are mapped.  For details, see *Note Automatic
     Overlay Debugging::.
`overlay load-target'
`overlay load'
     Re-read the overlay table from the inferior.  Normally, GDB
     re-reads the table GDB automatically each time the inferior stops,
     so this command should only be necessary if you have changed the
     overlay mapping yourself using GDB.  This command is only useful
     when using automatic overlay debugging.
`overlay list-overlays'
`overlay list'
     Display a list of the overlays currently mapped, along with their
     mapped addresses, load addresses, and sizes.
   Normally, when GDB prints a code address, it includes the name of
the function the address falls in:
     (gdb) print main
     $3 = {int ()} 0x11a0 <main>
When overlay debugging is enabled, GDB recognizes code in unmapped
overlays, and prints the names of unmapped functions with asterisks
around them.  For example, if `foo' is a function in an unmapped
overlay, GDB prints it this way:
     (gdb) overlay list
     No sections are mapped.
     (gdb) print foo
     $5 = {int (int)} 0x100000 <*foo*>
When `foo''s overlay is mapped, GDB prints the function's name normally:
     (gdb) overlay list
     Section .ov.foo.text, loaded at 0x100000 - 0x100034,
             mapped at 0x1016 - 0x104a
     (gdb) print foo
     $6 = {int (int)} 0x1016 <foo>
   When overlay debugging is enabled, GDB can find the correct address
for functions and variables in an overlay, whether or not the overlay
is mapped.  This allows most GDB commands, like `break' and
`disassemble', to work normally, even on unmapped code.  However, GDB's
breakpoint support has some limitations:
   * You can set breakpoints in functions in unmapped overlays, as long
     as GDB can write to the overlay at its load address.
   * GDB can not set hardware or simulator-based breakpoints in
     unmapped overlays.  However, if you set a breakpoint at the end of
     your overlay manager (and tell GDB which overlays are now mapped,
     if you are using manual overlay management), GDB will re-set its
     breakpoints properly.