Re: [PATCH] perf symbol: Do not use debug file as the binary type

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Thu, Aug 27, 2026 at 12:36:54PM -0700, Namhyung Kim wrote:
> Hello,
> 
> On Tue, Aug 25, 2026 at 09:23:45AM +0300, Adrian Hunter wrote:
> > dso__load() sets the binary type of a DSO to the type of the first symbol
> > source found. For a DSO with a separate debug file linked via
> > .gnu-debuglink, that is DSO_BINARY_TYPE__DEBUGLINK, which makes
> > dso__get_filename() return the name of the debug file instead of the file
> > that was actually executed.
> > 
> > Consumers that need to read instruction bytes, such as Intel PT decoding
> > in 'perf script', then read from the debug file and produce wrong
> > instructions.
> > 
> > Prefer DSO_BINARY_TYPE__BUILD_ID_CACHE, and otherwise
> > DSO_BINARY_TYPE__SYSTEM_PATH_DSO, over debug-only types, which restores
> > the behaviour of using a file that contains the executed instructions.
> > 
> > This is a workaround. Properly separating the binary file used for
> > instructions from the file used for debug symbols is left for later.
> > 
> > Example:
> > 
> >  Create a shared object with a separate .gnu_debuglink debug file. Note
> >  that 'objcopy --only-keep-debug' leaves .text as NOBITS, so instructions
> >  read from the debug file are zeros:
> > 
> >   # cat > foo.c << EOF
> >   unsigned long foo_work(unsigned long n)
> >   {
> >         unsigned long s = 0;
> > 
> >         for (unsigned long i = 0; i < n; i++)
> >                 s = s * 31 + i;
> >         return s;
> >   }
> >   EOF
> >   # cat > main.c << EOF
> >   #include <stdio.h>
> >   unsigned long foo_work(unsigned long n);
> >   int main(void)
> >   {
> >         printf("%lu\n", foo_work(1000));
> >         return 0;
> >   }
> >   EOF
> >   # gcc -g -O2 -shared -fPIC -o libfoo.so foo.c
> >   # gcc -g -O2 -o main main.c -L. -lfoo -Wl,-rpath,'$ORIGIN'
> >   # objcopy --only-keep-debug libfoo.so libfoo.so.debug
> >   # objcopy --strip-debug libfoo.so
> >   # objcopy --add-gnu-debuglink=libfoo.so.debug libfoo.so
> >   # perf record -e intel_pt//u ./main
> > 
> >  Note that branch samples must be requested, because it is the resolving
> >  of the branch target symbol that causes dso__load() to be called, and
> >  hence the binary type to be set, before the decoder walks the code.
> >  With '--itrace=e' alone, nothing loads symbols for libfoo.so, the binary
> >  type is left as DSO_BINARY_TYPE__NOT_FOUND, the correct file is read
> >  anyway, and no errors are reported either way.
> > 
> >  Before:
> > 
> >   # perf.before script --itrace=be 2>&1 | grep "instruction trace error"
> >    instruction trace error type 1 time 2350.467489498 cpu 9 pid 75634 tid 75634 ip 0x77d48480718f code 6: Trace doesn't match instruction
> >    instruction trace error type 1 time 2350.467489832 cpu 9 pid 75634 tid 75634 ip 0x77d484807341 code 6: Trace doesn't match instruction
> >    instruction trace error type 1 time 2350.467496412 cpu 9 pid 75634 tid 75634 ip 0x5b4de37a8074 code 6: Trace doesn't match instruction
> >    instruction trace error type 1 time 2350.467593393 cpu 9 pid 75634 tid 75634 ip 0x77d4848070d0 code 6: Trace doesn't match instruction
> >    instruction trace error type 1 time 2350.467593954 cpu 9 pid 75634 tid 75634 ip 0x77d4848075a8 code 6: Trace doesn't match instruction
> >    instruction trace error type 1 time 2350.467595728 cpu 9 pid 75634 tid 75634 ip 0x77d4848324de code 6: Trace doesn't match instruction
> >   6 instruction trace errors
> > 
> >  After:
> > 
> >   # perf script --itrace=be 2>&1 | grep "instruction trace error"
> >   #
> > 
> > Fixes: 5363c306787c8 ("perf symbol: Set binary_type of dso when loading")
> > Reported-by: Todd Lipcon <tlipcon@google.com>
> > Closes: https://lore.kernel.org/all/CAGH6UiG=RJLqBU3kLu9XJciPyPO1HZkbAPERguVUMRuWQgqf=A@mail.gmail.com/
> > Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> 
> Thanks for the patch and a test case.
> 
> Arnaldo, I can take this to the perf-tools tree for v7.3.

Ok!

- Arnaldo