selftests: arm64: Document what the SVE ptrace test is doing

Before we go modifying it further let's add some comments and output
clarifications explaining what this test is actually doing.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20210913125505.52619-5-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/tools/testing/selftests/arm64/fp/sve-ptrace.c b/tools/testing/selftests/arm64/fp/sve-ptrace.c
index d2ec48f..fc4a672 100644 (file)
--- a/tools/testing/selftests/arm64/fp/sve-ptrace.c
+++ b/tools/testing/selftests/arm64/fp/sve-ptrace.c
@@ -181,6 +181,7 @@ static int do_parent(pid_t child)
                }
        }
 
+       /* New process should start with FPSIMD registers only */
        sve = get_sve(pid, &svebuf, &svebufsz);
        if (!sve) {
                int e = errno;
@@ -191,14 +192,15 @@ static int do_parent(pid_t child)
 
                goto error;
        } else {
-               ksft_test_result_pass("get_sve\n");
+               ksft_test_result_pass("get_sve(FPSIMD)\n");
        }
 
        ksft_test_result((sve->flags & SVE_PT_REGS_MASK) == SVE_PT_REGS_FPSIMD,
-                        "FPSIMD registers\n");
+                        "Set FPSIMD registers\n");
        if ((sve->flags & SVE_PT_REGS_MASK) != SVE_PT_REGS_FPSIMD)
                goto error;
 
+       /* Try to set a known FPSIMD state via PT_REGS_SVE */
        fpsimd = (struct user_fpsimd_state *)((char *)sve +
                                              SVE_PT_FPSIMD_OFFSET);
        for (i = 0; i < 32; ++i) {
@@ -219,6 +221,7 @@ static int do_parent(pid_t child)
                goto error;
        }
 
+       /* Zero the first SVE Z register */
        vq = sve_vq_from_vl(sve->vl);
 
        newsvebufsz = SVE_PT_SVE_ZREG_OFFSET(vq, 1);
@@ -245,6 +248,7 @@ static int do_parent(pid_t child)
                goto error;
        }
 
+       /* Try to read back the value we just set */
        new_sve = get_sve(pid, &newsvebuf, &newsvebufsz);
        if (!new_sve) {
                int e = errno;
@@ -257,12 +261,13 @@ static int do_parent(pid_t child)
        }
 
        ksft_test_result((new_sve->flags & SVE_PT_REGS_MASK) == SVE_PT_REGS_SVE,
-                        "SVE registers\n");
+                        "Get SVE registers\n");
        if ((new_sve->flags & SVE_PT_REGS_MASK) != SVE_PT_REGS_SVE)
                goto error;
 
        dump_sve_regs(new_sve, 3, sizeof fpsimd->vregs[0]);
 
+       /* Verify that the register we set has the value we expected */
        p = (unsigned char *)new_sve + SVE_PT_SVE_ZREG_OFFSET(vq, 1);
        for (i = 0; i < sizeof fpsimd->vregs[0]; ++i) {
                unsigned char expected = i;