elf: Do not duplicate the GLIBC_TUNABLES string

The tunable parsing duplicates the tunable environment variable so it
null-terminates each one since it simplifies the later parsing. It has
the drawback of adding another point of failure (__minimal_malloc
failing), and the memory copy requires tuning the compiler to avoid mem
operations calls.

The parsing now tracks the tunable start and its size. The
dl-tunable-parse.h adds helper functions to help parsing, like a strcmp
that also checks for size and an iterator for suboptions that are
comma-separated (used on hwcap parsing by x86, powerpc, and s390x).

Since the environment variable is allocated on the stack by the kernel,
it is safe to keep the references to the suboptions for later parsing
of string tunables (as done by set_hwcaps by multiple architectures).

Checked on x86_64-linux-gnu, powerpc64le-linux-gnu, and
aarch64-linux-gnu.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

2 files changed, 18 insertions, 33 deletions

diff --git a/sysdeps/unix/sysv/linux/powerpc/cpu-features.c b/sysdeps/unix/sysv/linux/powerpc/cpu-features.c
index 7c6e20e702..390b3fd11a 100644
--- a/sysdeps/unix/sysv/linux/powerpc/cpu-features.c
+++ b/sysdeps/unix/sysv/linux/powerpc/cpu-features.c
@@ -20,6 +20,7 @@
 #include <stdint.h>
 #include <cpu-features.h>
 #include <elf/dl-tunables.h>
+#include <dl-tunables-parse.h>
 #include <unistd.h>
 #include <string.h>
 
@@ -43,41 +44,26 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
   struct cpu_features *cpu_features = &GLRO(dl_powerpc_cpu_features);
   unsigned long int tcbv_hwcap = cpu_features->hwcap;
   unsigned long int tcbv_hwcap2 = cpu_features->hwcap2;
-  const char *token = valp->strval;
-  do
+
+  struct tunable_str_comma_state_t ts;
+  tunable_str_comma_init (&ts, valp);
+
+  struct tunable_str_comma_t t;
+  while (tunable_str_comma_next (&ts, &t))
     {
-      const char *token_end, *feature;
-      bool disable;
-      size_t token_len, i, feature_len, offset = 0;
-      /* Find token separator or end of string.  */
-      for (token_end = token; *token_end != ','; token_end++)
-	if (*token_end == '\0')
-	  break;
+      if (t.len == 0)
+	continue;
 
-      /* Determine feature.  */
-      token_len = token_end - token;
-      if (*token == '-')
-	{
-	  disable = true;
-	  feature = token + 1;
-	  feature_len = token_len - 1;
-	}
-      else
-	{
-	  disable = false;
-	  feature = token;
-	  feature_len = token_len;
-	}
-      for (i = 0; i < array_length (hwcap_tunables); ++i)
+      size_t offset = 0;
+      for (int i = 0; i < array_length (hwcap_tunables); ++i)
 	{
 	  const char *hwcap_name = hwcap_names + offset;
 	  size_t hwcap_name_len = strlen (hwcap_name);
 	  /* Check the tunable name on the supported list.  */
-	  if (hwcap_name_len == feature_len
-	      && memcmp (feature, hwcap_name, feature_len) == 0)
+	  if (tunable_str_comma_strcmp (&t, hwcap_name, hwcap_name_len))
 	    {
 	      /* Update the hwcap and hwcap2 bits.  */
-	      if (disable)
+	      if (t.disable)
 		{
 		  /* Id is 1 for hwcap2 tunable.  */
 		  if (hwcap_tunables[i].id)
@@ -98,12 +84,7 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
 	    }
 	  offset += hwcap_name_len + 1;
 	}
-	token += token_len;
-	/* ... and skip token separator for next round.  */
-	if (*token == ',')
-	  token++;
     }
-  while (*token != '\0');
 }
 
 static inline void
diff --git a/sysdeps/unix/sysv/linux/powerpc/tst-hwcap-tunables.c b/sysdeps/unix/sysv/linux/powerpc/tst-hwcap-tunables.c
index 2631016a3a..049164f841 100644
--- a/sysdeps/unix/sysv/linux/powerpc/tst-hwcap-tunables.c
+++ b/sysdeps/unix/sysv/linux/powerpc/tst-hwcap-tunables.c
@@ -110,7 +110,11 @@ do_test (int argc, char *argv[])
 	run_test ("-arch_2_06", "__memcpy_power7");
       if (hwcap & PPC_FEATURE_ARCH_2_05)
 	run_test ("-arch_2_06,-arch_2_05","__memcpy_power6");
-      run_test ("-arch_2_06,-arch_2_05,-power5+,-power5,-power4", "__memcpy_power4");
+      run_test ("-arch_2_06,-arch_2_05,-power5+,-power5,-power4",
+		"__memcpy_power4");
+      /* Also run with valid, but empty settings.  */
+      run_test (",-,-arch_2_06,-arch_2_05,-power5+,-power5,,-power4,-",
+		"__memcpy_power4");
     }
   else
     {