docs/manual/using-buildroot-debugger: suggest '-ix' iso '-x' when loading gdbinit

From: Thomas De Schampheleire <[email protected]>

The gdbinit supplied by Buildroot does two things:
A. specify the sysroot where gdb can find shared libraries
B. mark the sysroot as a 'safe path' for its auto-load feature, to make sure
that pretty printers for libstdc++.so are added automatically (see commit 6fb3216a80c64c08375429d89497eaeec5622150)

When debugging a core file, and the gdbinit file is specified via '-x' rather than '-ix', then the order of these settings matters: If you first set the sysroot, then gdb will immediately start finding the shared libraries it needs for the core file, detect libstdc++ and its associated libstdc++-gdb.py file, then give a big warning about safe paths:

warning: File ".../i686-buildroot-linux-gnu/sysroot/lib/libstdc++.so.6.0.24-gdb.py"
auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load".
To enable execution of this file add

           add-auto-load-safe-path .../i686-buildroot-linux-gnu/sysroot/lib/libstdc++.so.6.0.24-gdb.py

line to your configuration file "/home/me/.gdbinit".
To completely disable this security protection add
set auto-load safe-path /
line to your configuration file "/home/me/.gdbinit".
For more information about this security protection see the "Auto-loading safe path" section in the GDB manual. E.g., run from the shell:
info "(gdb)Auto-loading safe path"

and the pretty printing code is not loaded. This is because the second line from the gdbinit file was not yet parsed at this point.

By changing the order (first configuring the safe path, then setting the sysroot), this issue does not appear and everything is as expected.

Note that when '-ix' were used instead of '-x' to pass the gdbinit file to gdb, then the order would not matter, because the entire gdbinit file would be parsed before considering the core file.
However, even though the Buildroot manual now suggests '-ix', users may not have noticed this change and continue to use '-x'.

Signed-off-by Thomas De Schampheleire <[email protected]>

---
  toolchain/helpers.mk | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

toolchain/helpers.mk +0 -0

index 1dfb52ac38..ef8e9a5f64 100644

Quoted 33 lines · Thomas De Schampheleire

From: Thomas De Schampheleire <[email protected]>

The gdbinit supplied by Buildroot does two things:
A. specify the sysroot where gdb can find shared libraries
B. mark the sysroot as a 'safe path' for its auto-load feature, to make sure
that pretty printers for libstdc++.so are added automatically (see commit 6fb3216a80c64c08375429d89497eaeec5622150)

When debugging a core file, and the gdbinit file is specified via '-x' rather than '-ix', then the order of these settings matters: If you first set the sysroot, then gdb will immediately start finding the shared libraries it needs for the core file, detect libstdc++ and its associated libstdc++-gdb.py file, then give a big warning about safe paths:

warning: File ".../i686-buildroot-linux-gnu/sysroot/lib/libstdc++.so.6.0.24-gdb.py"
auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load".
To enable execution of this file add

           add-auto-load-safe-path .../i686-buildroot-linux-gnu/sysroot/lib/libstdc++.so.6.0.24-gdb.py

line to your configuration file "/home/me/.gdbinit".
To completely disable this security protection add
set auto-load safe-path /
line to your configuration file "/home/me/.gdbinit".
For more information about this security protection see the "Auto-loading safe path" section in the GDB manual. E.g., run from the shell:
info "(gdb)Auto-loading safe path"

and the pretty printing code is not loaded. This is because the second line from the gdbinit file was not yet parsed at this point.

By changing the order (first configuring the safe path, then setting the sysroot), this issue does not appear and everything is as expected.

Quoted 5 lines

Note that when '-ix' were used instead of '-x' to pass the gdbinit file to gdb, then the order would not matter, because the entire gdbinit file would be parsed before considering the core file.
However, even though the Buildroot manual now suggests '-ix', users may not have noticed this change and continue to use '-x'.

Whaa, excellent, not content with fixing a bug once, you fix it twice!

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"Thomas" == Thomas De Schampheleire <[email protected]> writes:

From: Thomas De Schampheleire <[email protected]> The gdbinit supplied by Buildroot does two things:
A. specify the sysroot where gdb can find shared libraries
B. mark the sysroot as a 'safe path' for its auto-load feature, to make sure
that pretty printers for libstdc++.so are added automatically (see commit 6fb3216a80c64c08375429d89497eaeec5622150)

When debugging a core file, and the gdbinit file is specified via '-x' rather than '-ix', then the order of these settings matters: If you first set the sysroot, then gdb will immediately start finding the shared libraries it needs for the core file, detect libstdc++ and its associated libstdc++-gdb.py file, then give a big warning about safe paths:

warning: File ".../i686-buildroot-linux-gnu/sysroot/lib/libstdc++.so.6.0.24-gdb.py"
auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load".
To enable execution of this file add

          add-auto-load-safe-path .../i686-buildroot-linux-gnu/sysroot/lib/libstdc++.so.6.0.24-gdb.py

line to your configuration file "/home/me/.gdbinit".
To completely disable this security protection add
set auto-load safe-path /
line to your configuration file "/home/me/.gdbinit".
For more information about this security protection see the "Auto-loading safe path" section in the GDB manual. E.g., run from the shell:
info "(gdb)Auto-loading safe path"

and the pretty printing code is not loaded. This is because the second line from the gdbinit file was not yet parsed at this point.

By changing the order (first configuring the safe path, then setting the sysroot), this issue does not appear and everything is as expected.

Note that when '-ix' were used instead of '-x' to pass the gdbinit file to gdb, then the order would not matter, because the entire gdbinit file would be parsed before considering the core file.
However, even though the Buildroot manual now suggests '-ix', users may not have noticed this change and continue to use '-x'.

Signed-off-by Thomas De Schampheleire <[email protected]>

From: Thomas De Schampheleire <[email protected]>

A gdbinit file passed via '-x' will be read _after_ parsing any object/core file passed on the command-line. In cross-compilation context, this is particularly a problem when loading a core file, because without the 'sysroot' specified in the gdbinit file, it will give a lot of warnings, like:

warning: .dynamic section for "/lib/libstdc++.so.6" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/librt.so.1" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/libm.so.6" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/libgcc_s.so.1" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/libc.so.6" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/ld-linux.so.2" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/libanl.so.1" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/libdl.so.2" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/libpthread.so.0" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/usr/lib/libz.so.1" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/libnss_files.so.2" is not at the expected address (wrong library or version mismatch?)

warning: Could not load shared library symbols for 17 libraries, e.g. [...] Use the "info sharedlibrary" command to see the complete listing. Do you need "set solib-search-path" or "set sysroot"?

In contrast, the '-ix' option will load the specified gdbinit file _before_ parsing object/core files. This will remove said warnings.

See also: https://sourceware.org/bugzilla/show_bug.cgi?id=28330

Signed-off-by Thomas De Schampheleire <[email protected]>

---
  docs/manual/using-buildroot-debugger.txt | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

docs/manual/using-buildroot-debugger.txt +0 -0

index d5293beb53..9a8a7dfbaf 100644

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"Thomas" == Thomas De Schampheleire <[email protected]> writes:

From: Thomas De Schampheleire <[email protected]> A gdbinit file passed via '-x' will be read _after_ parsing any object/core file passed on the command-line. In cross-compilation context, this is particularly a problem when loading a core file, because without the 'sysroot' specified in the gdbinit file, it will give a lot of warnings, like:

warning: .dynamic section for "/lib/libstdc++.so.6" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/librt.so.1" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/libm.so.6" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/libgcc_s.so.1" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/libc.so.6" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/ld-linux.so.2" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/libanl.so.1" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/libdl.so.2" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/libpthread.so.0" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/usr/lib/libz.so.1" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/lib/libnss_files.so.2" is not at the expected address (wrong library or version mismatch?)

warning: Could not load shared library symbols for 17 libraries, e.g. [...] Use the "info sharedlibrary" command to see the complete listing. Do you need "set solib-search-path" or "set sysroot"?

In contrast, the '-ix' option will load the specified gdbinit file _before_ parsing object/core files. This will remove said warnings.

See also: https://sourceware.org/bugzilla/show_bug.cgi?id=28330

Signed-off-by Thomas De Schampheleire <[email protected]>