[lttng-dev] Trying to understand use of lttng enable-event --kernel --userspace-probe=

[Brian Hutchinson]

On Thu, May 18, 2023 at 3:16 PM Mathieu Desnoyers
<mathieu.desnoyers at efficios.com> wrote:
>
> On 2023-05-18 15:07, Brian Hutchinson wrote:
>
> [...]
>
> >>
> >> If you attach to an ELF symbol (function), then there is no USDT in
> >> play, so it should not be related to the issue you have.
> >
> > That is what I was thinking which is why I wanted to try it.
> >
> >>
> >> But if your functions happen to be inlined, then there will be nothing
> >> to attach to. Perhaps this is what happens there ?
> >
> > I don't see any evidence of anything being inlined in this module.  I
> > grepped the code to verify.
> >
> > Back to being stumped/stuck.
>
> Make sure to check the resulting assembler and ELF symbol tables.
>
> The compiler is free to inline various functions unless they are
> explicitly marked as __attribute__((noinline)). Also, if LTO is enabled,

I could put that in the code just to make sure.  It's a big function
so doubt it but I'll try anything at this point ha, ha.

I wondered if optimization could be doing it.

I can provide the standard yocto environment script that's being
source that was generated for the sdk:

$ cat environment-setup-aarch64-poky-linux


# Check for LD_LIBRARY_PATH being set, which can break SDK and
generally is a bad practice
# http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html#AEN80
# http://xahlee.info/UnixResource_dir/_/ldpath.html
# Only disable this check if you are absolutely know what you are doing!
if [ ! -z "${LD_LIBRARY_PATH:-}" ]; then
   echo "Your environment is misconfigured, you probably need to
'unset LD_LIBRARY_PATH'"
   echo "but please check why this was set in the first place and that
it's safe to unset."
   echo "The SDK will not operate correctly in most cases when
LD_LIBRARY_PATH is set."
   echo "For more references see:"
   echo "  http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html#AEN80"
   echo "  http://xahlee.info/UnixResource_dir/_/ldpath.html"
   return 1
fi
export SDKTARGETSYSROOT=/opt/poky/3.1.24/sysroots/aarch64-poky-linux
export PATH=/opt/poky/3.1.24/sysroots/x86_64-pokysdk-linux/usr/bin:/opt/poky/3.1.24/sysroots/x86_64-pokysdk-linux/usr/sbin:/opt/poky/3.1.24/sysroots/x86_64-pokysdk-linux/bin:/opt/poky/3.1.24/sysroots/x86_64-pokysdk-linux/sbin:/opt/poky/3.1.24/sysroots/x86_64-pokysdk-linux/usr/
bin/../x86_64-pokysdk-linux/bin:/opt/poky/3.1.24/sysroots/x86_64-pokysdk-linux/usr/bin/aarch64-poky-linux:/opt/poky/3.1.24/sysroots/x86_64-pokysdk-linux/usr/bin/aarch64-poky-linux-musl:"$PATH"
export PKG_CONFIG_SYSROOT_DIR=$SDKTARGETSYSROOT
export PKG_CONFIG_PATH=$SDKTARGETSYSROOT/usr/lib/pkgconfig:$SDKTARGETSYSROOT/usr/share/pkgconfig
export CONFIG_SITE=/opt/poky/3.1.24/site-config-aarch64-poky-linux
export OECORE_NATIVE_SYSROOT="/opt/poky/3.1.24/sysroots/x86_64-pokysdk-linux"
export OECORE_TARGET_SYSROOT="$SDKTARGETSYSROOT"
export OECORE_ACLOCAL_OPTS="-I
/opt/poky/3.1.24/sysroots/x86_64-pokysdk-linux/usr/share/aclocal"
export OECORE_BASELIB="lib"
export OECORE_TARGET_ARCH="aarch64"
export OECORE_TARGET_OS="linux"
unset command_not_found_handle
export CC="aarch64-poky-linux-gcc  -mcpu=cortex-a53+crc+crypto
-fstack-protector-strong  -D_FORTIFY_SOURCE=2 -Wformat
-Wformat-security -Werror=format-security --sysroot=$SDKTARGETSYSROOT"
export CXX="aarch64-poky-linux-g++  -mcpu=cortex-a53+crc+crypto
-fstack-protector-strong  -D_FORTIFY_SOURCE=2 -Wformat
-Wformat-security -Werror=format-security --sysroot=$SDKTARGETSYSROOT"
export CPP="aarch64-poky-linux-gcc -E  -mcpu=cortex-a53+crc+crypto
-fstack-protector-strong  -D_FORTIFY_SOURCE=2 -Wformat
-Wformat-security -Werror=format-security --sysroot=$SDKTARGETSYSROOT"
export AS="aarch64-poky-linux-as "
export LD="aarch64-poky-linux-ld  --sysroot=$SDKTARGETSYSROOT"
export GDB=aarch64-poky-linux-gdb
export STRIP=aarch64-poky-linux-strip
export RANLIB=aarch64-poky-linux-ranlib
export OBJCOPY=aarch64-poky-linux-objcopy
export OBJDUMP=aarch64-poky-linux-objdump
export READELF=aarch64-poky-linux-readelf
export AR=aarch64-poky-linux-ar
export NM=aarch64-poky-linux-nm
export M4=m4
export TARGET_PREFIX=aarch64-poky-linux-
export CONFIGURE_FLAGS="--target=aarch64-poky-linux
--host=aarch64-poky-linux --build=x86_64-linux
--with-libtool-sysroot=$SDKTARGETSYSROOT"
export CFLAGS=" -O2 -pipe -g -feliminate-unused-debug-types "
export CXXFLAGS=" -O2 -pipe -g -feliminate-unused-debug-types "
export LDFLAGS="-Wl,-O1 -Wl,--hash-style=gnu -Wl,--as-needed
-fstack-protector-strong -Wl,-z,relro,-z,now"
export CPPFLAGS=""
export KCFLAGS="--sysroot=$SDKTARGETSYSROOT"
export OECORE_DISTRO_VERSION="3.1.24"
export OECORE_SDK_VERSION="3.1.24"
export ARCH=arm64
export CROSS_COMPILE=aarch64-poky-linux-

# Append environment subscripts
if [ -d "$OECORE_TARGET_SYSROOT/environment-setup.d" ]; then
   for envfile in $OECORE_TARGET_SYSROOT/environment-setup.d/*.sh; do
           . $envfile
   done
fi
if [ -d "$OECORE_NATIVE_SYSROOT/environment-setup.d" ]; then
   for envfile in $OECORE_NATIVE_SYSROOT/environment-setup.d/*.sh; do
           . $envfile
   done
fi


> further optimization can be done at link-time.
>
> One purpose of the UST tracepoints is to be less fragile with respect to
> specific optimizations done by the compiler and linker, thus
> guaranteeing that whatever is instrumented with a tracepoint is indeed
> available for tracing.
>
> Also, double-check that the path you pass to --userspace-probe really
> targets your executable or .so binary file, and is not just a symbolic link.

It is full path.
>
> Thanks,
>
> Mathieu
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com
>