Re: [PATCH v2] aarch64: fix off-by-one in reading cpuinfo

[Richard Sandiford <richard.sandiford@arm.com>]

Philipp Tomsich <philipp.tomsich@vrull.eu> writes:
> Fixes: 341573406b39
>
> Don't subtract one from the result of strnlen() when trying to point
> to the first character after the current string.  This issue would
> cause individual characters (where the 128 byte buffers are stitched
> together) to be lost.
>
> gcc/ChangeLog:
>
> 	* config/aarch64/driver-aarch64.cc (readline): Fix off-by-one.
>
> gcc/testsuite/ChangeLog:
>
> 	* gcc.target/aarch64/cpunative/info_18: New test.
> 	* gcc.target/aarch64/cpunative/native_cpu_18.c: New test.
>
> Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
>
> ---
>
> Changes in v2:
> - Add a a regression test (as per review comment).
>
>  gcc/config/aarch64/driver-aarch64.cc              |  4 ++--
>  .../gcc.target/aarch64/cpunative/info_18          |  8 ++++++++
>  .../gcc.target/aarch64/cpunative/native_cpu_18.c  | 15 +++++++++++++++
>  3 files changed, 25 insertions(+), 2 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.target/aarch64/cpunative/info_18
>  create mode 100644 gcc/testsuite/gcc.target/aarch64/cpunative/native_cpu_18.c
>
> diff --git a/gcc/config/aarch64/driver-aarch64.cc b/gcc/config/aarch64/driver-aarch64.cc
> index 52ff537908e..48250e68034 100644
> --- a/gcc/config/aarch64/driver-aarch64.cc
> +++ b/gcc/config/aarch64/driver-aarch64.cc
> @@ -203,9 +203,9 @@ readline (FILE *f)
>  	return std::string ();
>        /* If we're not at the end of the line then override the
>  	 \0 added by fgets.  */
> -      last = strnlen (buf, size) - 1;
> +      last = strnlen (buf, size);
>      }
> -  while (!feof (f) && buf[last] != '\n');
> +  while (!feof (f) && (last > 0 && buf[last - 1] != '\n'));

Very minor, but: I think the normal GCC style would be to avoid the
extra (...).

OK with that change, thanks.  OK for backports too after a settling period.

Richard

>  
>    std::string result (buf);
>    free (buf);
> diff --git a/gcc/testsuite/gcc.target/aarch64/cpunative/info_18 b/gcc/testsuite/gcc.target/aarch64/cpunative/info_18
> new file mode 100644
> index 00000000000..25061a4abe8
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/cpunative/info_18
> @@ -0,0 +1,8 @@
> +processor	: 0
> +BogoMIPS	: 2000.00
> +Features	: fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics fphp asimdhp cpuid asimdrdm jscvt fcma lrcpc dcpop sha3 asimddp sha512 asimdfhm dit uscat ilrcpc flagm ssbs sb dcpodp flagm2 frint i8mm bf16 rng ecv
> +CPU implementer	: 0xc0
> +CPU architecture: 8
> +CPU variant	: 0x0
> +CPU part	: 0xac3
> +CPU revision	: 0
> diff --git a/gcc/testsuite/gcc.target/aarch64/cpunative/native_cpu_18.c b/gcc/testsuite/gcc.target/aarch64/cpunative/native_cpu_18.c
> new file mode 100644
> index 00000000000..b5f0a3005f5
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/cpunative/native_cpu_18.c
> @@ -0,0 +1,15 @@
> +/* { dg-do compile { target { { aarch64*-*-linux*} && native } } } */
> +/* { dg-set-compiler-env-var GCC_CPUINFO "$srcdir/gcc.target/aarch64/cpunative/info_18" } */
> +/* { dg-additional-options "-mcpu=native" } */
> +
> +int main()
> +{
> +  return 0;
> +}
> +
> +/* { dg-final { scan-assembler {\.arch armv8.6-a\+crc\+fp16\+aes\+sha3\+rng} } } */
> +
> +/* Test one where the boundary of buffer size would overwrite the last
> +   character read when stitching the fgets-calls together.  With the
> +   test data provided, this would truncate the 'sha512' into 'ha512'
> +   (dropping the 'sha3' feature). */