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btf: do not use the CHAR `encoding' bit for BTF

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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.
This commit is contained in:
Jose E. Marchesi 2022-07-22 12:40:50 +02:00
parent 6a11f2d974
commit 5df04a7aa8
2 changed files with 15 additions and 7 deletions
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4
gcc/btfout.cc
View file

@ -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);

18
gcc/testsuite/gcc.dg/debug/btf/btf-int-1.c
View file

@ -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;