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

[Gustavo Romero <gustavo.romero@linaro.org>]

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