Re: [PATCH 2/2] tests/tcg: Add multiarch test for Xfer:siginfo:read stub

[Gustavo Romero]

Hi Richard!

On 3/4/24 2:21 PM, Richard Henderson wrote:
> On 3/3/24 09:26, Gustavo Romero wrote:
> > Add multiarch test for testing if Xfer:siginfo:read query is properly
> > handled by gdbstub.
> >
> > Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
> > ---
> >   tests/tcg/multiarch/Makefile.target           | 10 ++++++-
> >   .../gdbstub/test-qxfer-siginfo-read.py        | 26 +++++++++++++++++++
> >   tests/tcg/multiarch/segfault.c                | 14 ++++++++++
> >   3 files changed, 49 insertions(+), 1 deletion(-)
> >   create mode 100644 tests/tcg/multiarch/gdbstub/test-qxfer-siginfo-read.py
> >   create mode 100644 tests/tcg/multiarch/segfault.c
> >
> > diff --git a/tests/tcg/multiarch/Makefile.target 
> > b/tests/tcg/multiarch/Makefile.target
> > index e10951a801..61cda9640e 100644
> > --- a/tests/tcg/multiarch/Makefile.target
> > +++ b/tests/tcg/multiarch/Makefile.target
> > @@ -80,6 +80,13 @@ run-gdbstub-qxfer-auxv-read: sha1
> >           --bin $< --test $(MULTIARCH_SRC)/gdbstub/test-qxfer-auxv-read.py, \
> >       basic gdbstub qXfer:auxv:read support)
> > +run-gdbstub-qxfer-siginfo-read: segfault
> > +    $(call run-test, $@, $(GDB_SCRIPT) \
> > +        --gdb $(GDB) \
> > +        --qemu $(QEMU) --qargs "$(QEMU_OPTS)" \
> > +        --bin "$< -s" --test 
> > $(MULTIARCH_SRC)/gdbstub/test-qxfer-siginfo-read.py, \
> > +    basic gdbstub qXfer:siginfo:read support)
> > +
> >   run-gdbstub-proc-mappings: sha1
> >       $(call run-test, $@, $(GDB_SCRIPT) \
> >           --gdb $(GDB) \
> > @@ -122,7 +129,8 @@ endif
> >   EXTRA_RUNS += run-gdbstub-sha1 run-gdbstub-qxfer-auxv-read \
> >             run-gdbstub-proc-mappings run-gdbstub-thread-breakpoint \
> >             run-gdbstub-registers run-gdbstub-prot-none \
> > -          run-gdbstub-catch-syscalls
> > +          run-gdbstub-catch-syscalls \
> > +          run-gdbstub-qxfer-siginfo-read
> >   # ARM Compatible Semi Hosting Tests
> >   #
> > diff --git a/tests/tcg/multiarch/gdbstub/test-qxfer-siginfo-read.py 
> > b/tests/tcg/multiarch/gdbstub/test-qxfer-siginfo-read.py
> > new file mode 100644
> > index 0000000000..862596b07a
> > --- /dev/null
> > +++ b/tests/tcg/multiarch/gdbstub/test-qxfer-siginfo-read.py
> > @@ -0,0 +1,26 @@
> > +from __future__ import print_function
> > +#
> > +# Test gdbstub Xfer:siginfo:read stub.
> > +#
> > +# The test runs a binary that causes a SIGSEGV and then looks for additional
> > +# info about the signal through printing GDB's '$_siginfo' special variable,
> > +# which sends a Xfer:siginfo:read query to the gdbstub.
> > +#
> > +# The binary causes a SIGSEGV at dereferencing a pointer with value 0xdeadbeef,
> > +# so the test looks for and checks if this address is correctly reported by the
> > +# gdbstub.
> > +#
> > +# This is launched via tests/guest-debug/run-test.py
> > +#
> > +
> > +import gdb
> > +from test_gdbstub import main, report
> > +
> > +def run_test():
> > +    "Run through the test"
> > +
> > +    gdb.execute("continue", False, True)
> > +    resp = gdb.execute("print/x $_siginfo", False, True)
> > +    report(resp.find("si_addr = 0xdeadbeef"), "Found fault address.")
> > +
> > +main(run_test)
> > diff --git a/tests/tcg/multiarch/segfault.c b/tests/tcg/multiarch/segfault.c
> > new file mode 100644
> > index 0000000000..e6c8ff31ca
> > --- /dev/null
> > +++ b/tests/tcg/multiarch/segfault.c
> > @@ -0,0 +1,14 @@
> > +#include <stdio.h>
> > +#include <string.h>
> > +
> > +/* Cause a segfault for testing purposes. */
> > +
> > +int main(int argc, char *argv[])
> > +{
> > +    int *ptr = (void *)0xdeadbeef;
> > +
> > +    if (argc == 2 && strcmp(argv[1], "-s") == 0) {
> > +        /* Cause segfault. */
> > +        printf("%d\n", *ptr);
> > +    }
> > +}
>
> Any reason SIGSEGV is interesting?

I'm particularly interested in the SIGSEGV because that's the signal
generated on a MTE tag mismatch. GDB uses the si_code to show
additional info on the fault, for instance:

gromero@arm64:~$ gdb -q
(gdb) target remote amd:1234
Remote debugging using amd:1234
Reading /home/gromero/git/qemu/build/mte_t from remote target...
warning: File transfers from remote targets can be slow. Use "set sysroot" to 
access files locally instead.
Reading /home/gromero/git/qemu/build/mte_t from remote target...
Reading symbols from target:/home/gromero/git/qemu/build/mte_t...
Failed to read a valid object file image from memory.
0x0000000000400580 in _start ()
(gdb) c
Continuing.

Program received signal SIGSEGV, Segmentation fault
Memory tag violation           <============ (the info I'm keen on)
Fault address unavailable.
0x0000000000407290 in puts ()
(gdb)


> Perhaps just abort for SIGABRT instead?

Although this can make a simpler test, the test can't control
the si_addr value easily, which I think is interesting to be tested.

Why do you prefer SIGABRT?


> A test using setitimer to raise SIGALRM would test the async path.

SIGLARM doesn't generate any interesting siginfo?

gromero@arm64:~$ gdb -q ./sigalrm
Reading symbols from ./sigalrm...
(gdb) run
Starting program: /home/gromero/sigalrm

Program terminated with signal SIGALRM, Alarm clock.
The program no longer exists.
(gdb) p $_siginfo
$1 = void
(gdb)


Cheers,
Gustavo