[gcc r13-1937] btf: do not use the CHAR `encoding' bit for BTF

[Jose E. Marchesi]

https://gcc.gnu.org/g:5df04a7aa837a13b0e14d269c37bd3871d86bf08

commit r13-1937-g5df04a7aa837a13b0e14d269c37bd3871d86bf08
Author: Jose E. Marchesi <jose.marchesi@oracle.com>
Date:   Fri Jul 22 12:40:50 2022 +0200

    btf: do not use the CHAR `encoding' bit for BTF
    
    Contrary to CTF and our previous expectations, as per [1], turns out
    that in BTF:
    
    1) The `encoding' field in integer types shall not be treated as a
       bitmap, but as an enumerated, i.e. these bits are exclusive to each
       other.
    
    2) The CHAR bit in `encoding' shall _not_ be set when emitting types
       for char nor `unsigned char'.
    
    Consequently this patch clears the CHAR bit before emitting the
    variable part of BTF integral types.  It also updates the testsuite
    accordingly, expanding it to check for BOOL bits.
    
    [1] https://lore.kernel.org/bpf/a73586ad-f2dc-0401-1eba-2004357b7edf@fb.com/T/#t
    
    gcc/ChangeLog:
    
            * btfout.cc (output_asm_btf_vlen_bytes): Do not use the CHAR
            encoding bit in BTF.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/debug/btf/btf-int-1.c: Do not check for char bits in
            bti_encoding and check for bool bits.

Diff:
---
 gcc/btfout.cc                              |  4 ++++
 gcc/testsuite/gcc.dg/debug/btf/btf-int-1.c | 18 +++++++++++-------
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/gcc/btfout.cc b/gcc/btfout.cc
index 594cba84910..997a33fa089 100644
--- a/gcc/btfout.cc
+++ b/gcc/btfout.cc
@@ -918,6 +918,10 @@ output_asm_btf_vlen_bytes (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
       if (dtd->dtd_data.ctti_size < 1)
 	break;
 
+      /* In BTF the CHAR `encoding' seems to not be used, so clear it
+         here.  */
+      dtd->dtd_u.dtu_enc.cte_format &= ~BTF_INT_CHAR;
+
       encoding = BTF_INT_DATA (dtd->dtd_u.dtu_enc.cte_format,
 			       dtd->dtd_u.dtu_enc.cte_offset,
 			       dtd->dtd_u.dtu_enc.cte_bits);
diff --git a/gcc/testsuite/gcc.dg/debug/btf/btf-int-1.c b/gcc/testsuite/gcc.dg/debug/btf/btf-int-1.c
index 2381decd6ff..87d9758e9cb 100644
--- a/gcc/testsuite/gcc.dg/debug/btf/btf-int-1.c
+++ b/gcc/testsuite/gcc.dg/debug/btf/btf-int-1.c
@@ -4,7 +4,8 @@
    | 0 | encoding | offset | 00 | bits |
    encoding:
      signed  1 << 24
-     char    2 << 24
+     char    2 << 24  (not used)
+     bool    4 << 24
 
    All offsets in this test should be 0.
    This test does _not_ check number of bits, as it may vary between targets.
@@ -13,13 +14,14 @@
 /* { dg-do compile } */
 /* { dg-options "-O0 -gbtf -dA" } */
 
-/* Check for 8 BTF_KIND_INT types.  */
-/* { dg-final { scan-assembler-times "\[\t \]0x1000000\[\t \]+\[^\n\]*btt_info" 8 } } */
+/* Check for 9 BTF_KIND_INT types.  */
+/* { dg-final { scan-assembler-times "\[\t \]0x1000000\[\t \]+\[^\n\]*btt_info" 9 } } */
 
-/* Check the signed/char flags, but not bit size. */
-/* { dg-final { scan-assembler-times "\[\t \]0x10000..\[\t \]+\[^\n\]*bti_encoding" 3 } } */
-/* { dg-final { scan-assembler-times "\[\t \]0x20000..\[\t \]+\[^\n\]*bti_encoding" 1 } } */
-/* { dg-final { scan-assembler-times "\[\t \]0x30000..\[\t \]+\[^\n\]*bti_encoding" 1 } } */
+/* Check the signed flags, but not bit size. */
+/* { dg-final { scan-assembler-times "\[\t \]0x10000..\[\t \]+\[^\n\]*bti_encoding" 4 } } */
+/* { dg-final { scan-assembler-times "\[\t \]0x..\[\t \]+\[^\n\]*bti_encoding" 3 } } */
+/* { dg-final { scan-assembler-times "\[\t \]0x.\[\t \]+\[^\n\]*bti_encoding" 1 } } */
+/* { dg-final { scan-assembler-times "\[\t \]0x40000..\[\t \]+\[^\n\]*bti_encoding" 1 } } */
 
 /* Check that there is a string entry for each type name.  */
 /* { dg-final { scan-assembler-times "ascii \"unsigned char.0\"\[\t \]+\[^\n\]*btf_string" 1 } } */
@@ -42,3 +44,5 @@ signed int f = -66;
 
 unsigned long int g = 77;
 signed long int h = 88;
+
+_Bool x = 1;