[gcc r13-3127] aarch64: fix off-by-one in reading cpuinfo

[Philipp Tomsich <ptomsich@gcc.gnu.org>]

https://gcc.gnu.org/g:b1cfbccc41de6aec950c0f662e7e85ab34bfff8a

commit r13-3127-gb1cfbccc41de6aec950c0f662e7e85ab34bfff8a
Author: Philipp Tomsich <philipp.tomsich@vrull.eu>
Date:   Mon Oct 3 21:59:50 2022 +0200

    aarch64: fix off-by-one in reading cpuinfo
    
    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>

Diff:
---
 gcc/config/aarch64/driver-aarch64.cc                      |  4 ++--
 gcc/testsuite/gcc.target/aarch64/cpunative/info_18        |  8 ++++++++
 .../gcc.target/aarch64/cpunative/native_cpu_18.c          | 15 +++++++++++++++
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/gcc/config/aarch64/driver-aarch64.cc b/gcc/config/aarch64/driver-aarch64.cc
index 52ff537908e..2ae47c020d3 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');
 
   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). */