Re: [PATCH v4 1/3] aarch64: add debug comments to feature properties in .note.gnu.property

[Matthieu Longo]

On 2025-06-11 15:59, Richard Sandiford wrote:

Matthieu Longo <matthieu.lo...@arm.com> writes:

GNU properties are emitted to provide some information about the features
used in the generated code like BTI, GCS, or PAC. However, no debug
comment are emitted in the generated assembly even if -dA is provided.
It makes understanding the information stored in the .note.gnu.property
section more difficult than needed.

This patch adds assembly comments (if -dA is provided) next to the GNU
properties. For instance, if BTI and PAC are enabled, it will emit:
   .word  0x3  // GNU_PROPERTY_AARCH64_FEATURE_1_AND (BTI, PAC)

gcc/ChangeLog:

        * config/aarch64/aarch64.cc
        (aarch64_file_end_indicate_exec_stack): Emit assembly comments.

gcc/testsuite/ChangeLog:

        * gcc.target/aarch64/bti-1.c: Emit assembly comments, and update
        test assertion.

OK, thanks.

Richard

Merged into master: 6eb0dc067dad1fe745e83d4e113c1b2ea0ffed8c

---
  gcc/config/aarch64/aarch64.cc            | 35 ++++++++++++++++++++++--
  gcc/testsuite/gcc.target/aarch64/bti-1.c | 13 +++++----
  2 files changed, 40 insertions(+), 8 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 59ac08483f4..bc6e16ce807 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -30028,10 +30028,41 @@ aarch64_file_end_indicate_exec_stack ()
         type   = GNU_PROPERTY_AARCH64_FEATURE_1_AND
         datasz = 4
         data   = feature_1_and.  */
-      assemble_integer (GEN_INT (GNU_PROPERTY_AARCH64_FEATURE_1_AND), 4, 32, 
1);
+      fputs (integer_asm_op (4, true), asm_out_file);
+      fprint_whex (asm_out_file, GNU_PROPERTY_AARCH64_FEATURE_1_AND);
+      putc ('\n', asm_out_file);
        assemble_integer (GEN_INT (4), 4, 32, 1);
-      assemble_integer (GEN_INT (feature_1_and), 4, 32, 1);

+ fputs (integer_asm_op (4, true), asm_out_file);

+      fprint_whex (asm_out_file, feature_1_and);
+      if (flag_debug_asm)
+       {
+         struct flag_name
+         {
+           unsigned int mask;
+           const char *name;
+         };
+         static const flag_name flags[] = {
+           { GNU_PROPERTY_AARCH64_FEATURE_1_BTI, "BTI" },
+           { GNU_PROPERTY_AARCH64_FEATURE_1_PAC, "PAC" },
+           { GNU_PROPERTY_AARCH64_FEATURE_1_GCS, "GCS" },
+         };
+
+         const char *separator = "";
+         std::string s_features;
+         for (auto &flag : flags)
+           if (feature_1_and & flag.mask)
+             {
+               s_features.append (separator).append (flag.name);
+               separator = ", ";
+             }
+
+         asm_fprintf (asm_out_file,
+                      "\t%s GNU_PROPERTY_AARCH64_FEATURE_1_AND (%s)\n",
+                      ASM_COMMENT_START, s_features.c_str ());
+       }
+      else
+       putc ('\n', asm_out_file);
        /* Pad the size of the note to the required alignment.  */
        assemble_align (POINTER_SIZE);
      }
diff --git a/gcc/testsuite/gcc.target/aarch64/bti-1.c 
b/gcc/testsuite/gcc.target/aarch64/bti-1.c
index 5a556b08ed1..53dc2d3cd8b 100644
--- a/gcc/testsuite/gcc.target/aarch64/bti-1.c
+++ b/gcc/testsuite/gcc.target/aarch64/bti-1.c
@@ -1,6 +1,6 @@
  /* { dg-do compile } */
  /* -Os to create jump table.  */
-/* { dg-options "-Os" } */
+/* { dg-options "-Os -dA" } */
  /* { dg-require-effective-target lp64 } */
  /* If configured with --enable-standard-branch-protection, don't use
     command line option.  */
@@ -44,8 +44,8 @@ f_jump_table (int y, int n)
    return (y == 0)? y+1:4;
  }
  /* f_jump_table should have PACIASP and AUTIASP.  */
-/* { dg-final { scan-assembler-times "hint\t25" 1 } } */
-/* { dg-final { scan-assembler-times "hint\t29" 1 } } */
+/* { dg-final { scan-assembler-times "hint\t25 // paciasp" 1 } } */
+/* { dg-final { scan-assembler-times "hint\t29 // autiasp" 1 } } */

int

  f_label_address ()
@@ -59,6 +59,7 @@ lab2:
    addr = &&lab1;
    return 2;
  }
-/* { dg-final { scan-assembler-times "hint\t34" 1 } } */
-/* { dg-final { scan-assembler-times "hint\t36" 12 } } */
-/* { dg-final { scan-assembler ".note.gnu.property" { target *-*-linux* } } } 
*/
+/* { dg-final { scan-assembler-times "hint\t34 // bti c" 1 } } */
+/* { dg-final { scan-assembler-times "hint\t36 // bti j" 12 } } */
+/* { dg-final { scan-assembler "\.section\t\.note\.gnu\.property" { target 
*-*-linux* } } } */
+/* { dg-final { scan-assembler "\.word\t0x7\t\/\/ 
GNU_PROPERTY_AARCH64_FEATURE_1_AND \\(BTI, PAC, GCS\\)" { target *-*-linux* } } } */
\ No newline at end of file