On 7/22/22 4:23 AM, Jose E. Marchesi via Gcc-patches wrote:
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'.
Hmm...well. At this time, I suggest we make a note of this in the btf.h
for posterity that BTF_INT_CHAR is to not be used (i.e., BTF_INT_CHAR
should not be set for char / 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-2004357b7...@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.
---
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 31af50521da..576f73d47cf 100644
--- a/gcc/btfout.cc
+++ b/gcc/btfout.cc
@@ -914,6 +914,10 @@ 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;
+
[Added David Faust]
What do you think about doing this in btf_dtd_emit_preprocess_cb () for
types where kind == BTF_KIND_INT. This is the place where BTF specific
massaging of type info takes place.
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;
