Re: [PATCH v2 1/4] gdb/aarch64: record/replay support for LRCPC3

[Thiago Jung Bauermann <thiago.bauermann@linaro.org>]

Hello Ezra,

Mostly looks good to me. Just a couple of comments in
allow_aarch64_lrcpc3_tests and a question on how to test:

<Ezra.Sitorus@arm.com> writes:

> diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
> index 28709004..3f3197cb 100644
> --- a/gdb/testsuite/lib/gdb.exp
> +++ b/gdb/testsuite/lib/gdb.exp
> @@ -5287,6 +5287,69 @@ gdb_caching_proc allow_aarch64_fpmr_tests {} {
>      return $allow_fpmr_tests
>  }
>  
> +# Run a test on the target to see if it supports AArch64 LRCPC3 (Load-Acquire
> +# RCpc instructions) extensions.  Return 1 if so, 0 if it does not.  Note this
> +# causes a restart of GDB.
> +
> +gdb_caching_proc allow_aarch64_lrcpc3_tests {} {
> +    global srcdir subdir gdb_prompt inferior_exited_re
> +
> +    set me "allow_aarch64_lrcpc3_tests"
> +
> +    if { ![is_aarch64_target] } {
> +	return 0
> +    }
> +
> +    # Take the opportunity to check whether the toolchain knows about LRCPC3.
> +    set compile_flags "{additional_flags=-march=armv8-a+rcpc3}"
> +
> +    # Compile a program that tests the LRCPC3 feature.
> +    set src {
> +	#include <stdbool.h>
> +	#include <sys/auxv.h>
> +
> +	/* Feature check for LRCPC3.  */
> +	#ifndef HWCAP_LRCPC3
> +	#define HWCAP_LRCPC3 (1ULL << 46)
> +	#endif

In the system headers, this constant is called HWCAP2_LRCPC3.

> +
> +	int main (void) {
> +	    bool lrcpc3_supported = getauxval (AT_HWCAP2) & HWCAP_LRCPC3;
> +
> +	    /* Return success if LRCPC3 is supported.  */
> +	    return !lrcpc3_supported;
> +	}
> +    }
> +
> +    if {![gdb_simple_compile $me $src executable $compile_flags]} {
> +	return 0
> +    }
> +
> +    # Compilation succeeded so now run it via gdb.
> +    clean_restart
> +    gdb_load $obj
> +    gdb_run_cmd
> +    gdb_expect {
> +	-re ".*Illegal instruction.*${gdb_prompt} $" {
> +	    verbose -log "\n$me lrcpc3 support not detected"
> +	    set allow_lrcpc3_tests 0
> +	}
> +	-re ".*$inferior_exited_re normally.*${gdb_prompt} $" {
> +	    verbose -log "\n$me: lrcpc3 support detected"
> +	    set allow_lrcpc3_tests 1
> +	}
> +	default {
> +	  warning "\n$me: default case taken"
> +	    set allow_lrcpc3_tests 0
> +	}
> +    }

The test program in v1 tried to execute an instruction to detect whether
LRCPC3 is supported, and in v2 it checks a bit in HWCAP. Nothing wrong
with that, but the gdb_expect above needs to be adapted accordingly. On
a machine which doesn't support the feature I see a WARNING, but the
test program just behaved as expected:

(gdb) file /home/bauermann/.cache/builds/gdb-native/gdb/testsuite/temp/1223/allow_aarch64_lrcpc3_tests.x
Reading symbols from /home/bauermann/.cache/builds/gdb-native/gdb/testsuite/temp/1223/allow_aarch64_lrcpc3_tests.x...
(gdb) run 
Starting program: /home/bauermann/.cache/builds/gdb-native/gdb/testsuite/temp/1223/allow_aarch64_lrcpc3_tests.x 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/aarch64-linux-gnu/libthread_db.so.1".
[Inferior 1 (process 1299) exited with code 01]
(gdb) WARNING: 
allow_aarch64_lrcpc3_tests: default case taken
gdb_caching_proc allow_aarch64_lrcpc3_tests caused gdb_exit to be called
  gdb_caching_proc allow_aarch64_lrcpc3_tests marked as called
  gdb_caching_proc get_compiler_info_1 marked as called
  gdb_caching_proc is_aarch32_target marked as called
  gdb_caching_proc universal_compile_options_c marked as called
UNSUPPORTED: gdb.reverse/aarch64-lrcpc3.exp: require failed: allow_aarch64_lrcpc3_tests
testcase /home/bauermann/src/binutils-gdb/gdb/testsuite/gdb.reverse/aarch64-lrcpc3.exp completed in 26 seconds

By the way, is there something specific I need to do to get an FVP
supporting LRCPC3? I set up FVP with:

$ shrinkwrap build --overlay=arch/v9.6.yaml ns-edk2.yaml

But then inside the guest the CPU features in /proc/cpuinfo and the
HWCAP2 don't mention LRCPC3. If I hard-code the testcase to run anyway,
then the inferior dies with a SIGILL.

> +    gdb_exit
> +    remote_file build delete $obj
> +
> +    verbose "$me:  returning $allow_lrcpc3_tests" 2
> +    return $allow_lrcpc3_tests
> +}
> +
>  # Run a test on the target to see if it supports AArch64 MOPS (Memory
>  # Operations) extensions.  Return 1 if so, 0 if it does not.  Note this
>  # causes a restart of GDB.

-- 
Thiago