gdb: Overlay Commands
14.2 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 
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.
Info Catalog
gdb: How Overlays Work
gdb: Overlays
gdb: Automatic Overlay Debugging