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>

1 files changed, 43 insertions, 75 deletions

diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
index 5697885..ef96148 100644
--- a/sysdeps/x86/cpu-tunables.c
+++ b/sysdeps/x86/cpu-tunables.c
@@ -24,11 +24,12 @@
 #include <string.h>
 #include <cpu-features.h>
 #include <ldsodefs.h>
+#include <dl-tunables-parse.h>
 #include <dl-symbol-redir-ifunc.h>
 
 #define CHECK_GLIBC_IFUNC_CPU_OFF(f, cpu_features, name, len)		\
   _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);	\
-  if (memcmp (f, #name, len) == 0)					\
+  if (tunable_str_comma_strcmp_cte (&f, #name))				\
     {									\
       CPU_FEATURE_UNSET (cpu_features, name)				\
       break;								\
@@ -38,7 +39,7 @@
    which isn't available.  */
 #define CHECK_GLIBC_IFUNC_PREFERRED_OFF(f, cpu_features, name, len)	\
   _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);	\
-  if (memcmp (f, #name, len) == 0)					\
+  if (tunable_str_comma_strcmp_cte (&f, #name) == 0)			\
     {									\
       cpu_features->preferred[index_arch_##name]			\
 	&= ~bit_arch_##name;						\
@@ -46,12 +47,11 @@
     }
 
 /* Enable/disable a preferred feature NAME.  */
-#define CHECK_GLIBC_IFUNC_PREFERRED_BOTH(f, cpu_features, name,	\
-					  disable, len)			\
+#define CHECK_GLIBC_IFUNC_PREFERRED_BOTH(f, cpu_features, name, len)	\
   _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);	\
-  if (memcmp (f, #name, len) == 0)					\
+  if (tunable_str_comma_strcmp_cte (&f, #name))				\
     {									\
-      if (disable)							\
+      if (f.disable)							\
 	cpu_features->preferred[index_arch_##name] &= ~bit_arch_##name;	\
       else								\
 	cpu_features->preferred[index_arch_##name] |= bit_arch_##name;	\
@@ -61,11 +61,11 @@
 /* Enable/disable a preferred feature NAME.  Enable a preferred feature
    only if the feature NEED is usable.  */
 #define CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH(f, cpu_features, name,	\
-					       need, disable, len)	\
+					      need, len)		\
   _Static_assert (sizeof (#name) - 1 == len, #name " != " #len);	\
-  if (memcmp (f, #name, len) == 0)					\
+  if (tunable_str_comma_strcmp_cte (&f, #name))				\
     {									\
-      if (disable)							\
+      if (f.disable)							\
 	cpu_features->preferred[index_arch_##name] &= ~bit_arch_##name;	\
       else if (CPU_FEATURE_USABLE_P (cpu_features, need))		\
 	cpu_features->preferred[index_arch_##name] |= bit_arch_##name;	\
@@ -93,38 +93,20 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
      NOTE: the IFUNC selection may change over time.  Please check all
      multiarch implementations when experimenting.  */
 
-  const char *p = valp->strval, *c;
   struct cpu_features *cpu_features = &GLRO(dl_x86_cpu_features);
-  size_t len;
 
-  do
-    {
-      const char *n;
-      bool disable;
-      size_t nl;
-
-      for (c = p; *c != ','; c++)
-	if (*c == '\0')
-	  break;
+  struct tunable_str_comma_state_t ts;
+  tunable_str_comma_init (&ts, valp);
 
-      len = c - p;
-      disable = *p == '-';
-      if (disable)
-	{
-	  n = p + 1;
-	  nl = len - 1;
-	}
-      else
-	{
-	  n = p;
-	  nl = len;
-	}
-      switch (nl)
+  struct tunable_str_comma_t n;
+  while (tunable_str_comma_next (&ts, &n))
+    {
+      switch (n.len)
 	{
 	default:
 	  break;
 	case 3:
-	  if (disable)
+	  if (n.disable)
 	    {
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX, 3);
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, CX8, 3);
@@ -135,7 +117,7 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
 	    }
 	  break;
 	case 4:
-	  if (disable)
+	  if (n.disable)
 	    {
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX2, 4);
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, BMI1, 4);
@@ -149,7 +131,7 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
 	    }
 	  break;
 	case 5:
-	  if (disable)
+	  if (n.disable)
 	    {
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, LZCNT, 5);
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, MOVBE, 5);
@@ -159,12 +141,12 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
 	    }
 	  break;
 	case 6:
-	  if (disable)
+	  if (n.disable)
 	    {
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, POPCNT, 6);
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SSE4_1, 6);
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SSE4_2, 6);
-	      if (memcmp (n, "XSAVEC", 6) == 0)
+	      if (memcmp (n.str, "XSAVEC", 6) == 0)
 		{
 		  /* Update xsave_state_size to XSAVE state size.  */
 		  cpu_features->xsave_state_size
@@ -174,14 +156,14 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
 	    }
 	  break;
 	case 7:
-	  if (disable)
+	  if (n.disable)
 	    {
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512F, 7);
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, OSXSAVE, 7);
 	    }
 	  break;
 	case 8:
-	  if (disable)
+	  if (n.disable)
 	    {
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512CD, 8);
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512BW, 8);
@@ -190,86 +172,72 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512PF, 8);
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, AVX512VL, 8);
 	    }
-	  CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Slow_BSF,
-					    disable, 8);
+	  CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Slow_BSF, 8);
 	  break;
 	case 11:
 	    {
-	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
-						Prefer_ERMS,
-						disable, 11);
-	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
-						Prefer_FSRM,
-						disable, 11);
+	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Prefer_ERMS,
+						11);
+	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Prefer_FSRM,
+						11);
 	      CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH (n, cpu_features,
 						     Slow_SSE4_2,
 						     SSE4_2,
-						     disable, 11);
+						     11);
 	    }
 	  break;
 	case 15:
 	    {
 	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
-						Fast_Rep_String,
-						disable, 15);
+						Fast_Rep_String, 15);
 	    }
 	  break;
 	case 16:
 	    {
 	      CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
-		(n, cpu_features, Prefer_No_AVX512, AVX512F,
-		 disable, 16);
+		(n, cpu_features, Prefer_No_AVX512, AVX512F, 16);
 	    }
 	  break;
 	case 18:
 	    {
 	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
-						Fast_Copy_Backward,
-						disable, 18);
+						Fast_Copy_Backward, 18);
 	    }
 	  break;
 	case 19:
 	    {
 	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
-						Fast_Unaligned_Load,
-						disable, 19);
+						Fast_Unaligned_Load, 19);
 	      CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
-						Fast_Unaligned_Copy,
-						disable, 19);
+						Fast_Unaligned_Copy, 19);
 	    }
 	  break;
 	case 20:
 	    {
 	      CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
-		(n, cpu_features, Prefer_No_VZEROUPPER, AVX, disable,
-		 20);
+		(n, cpu_features, Prefer_No_VZEROUPPER, AVX, 20);
 	    }
 	  break;
 	case 23:
 	    {
 	      CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
-		(n, cpu_features, AVX_Fast_Unaligned_Load, AVX,
-		 disable, 23);
+		(n, cpu_features, AVX_Fast_Unaligned_Load, AVX, 23);
 	    }
 	  break;
 	case 24:
 	    {
 	      CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
-		(n, cpu_features, MathVec_Prefer_No_AVX512, AVX512F,
-		 disable, 24);
+		(n, cpu_features, MathVec_Prefer_No_AVX512, AVX512F, 24);
 	    }
 	  break;
 	case 26:
 	    {
 	      CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
-		(n, cpu_features, Prefer_PMINUB_for_stringop, SSE2,
-		 disable, 26);
+		(n, cpu_features, Prefer_PMINUB_for_stringop, SSE2, 26);
 	    }
 	  break;
 	}
-      p += len + 1;
     }
-  while (*c != '\0');
 }
 
 #if CET_ENABLED
@@ -277,11 +245,11 @@ attribute_hidden
 void
 TUNABLE_CALLBACK (set_x86_ibt) (tunable_val_t *valp)
 {
-  if (memcmp (valp->strval, "on", sizeof ("on")) == 0)
+  if (tunable_strcmp_cte (valp, "on"))
     GL(dl_x86_feature_control).ibt = cet_always_on;
-  else if (memcmp (valp->strval, "off", sizeof ("off")) == 0)
+  else if (tunable_strcmp_cte (valp, "off"))
     GL(dl_x86_feature_control).ibt = cet_always_off;
-  else if (memcmp (valp->strval, "permissive", sizeof ("permissive")) == 0)
+  else if (tunable_strcmp_cte (valp, "permissive"))
     GL(dl_x86_feature_control).ibt = cet_permissive;
 }
 
@@ -289,11 +257,11 @@ attribute_hidden
 void
 TUNABLE_CALLBACK (set_x86_shstk) (tunable_val_t *valp)
 {
-  if (memcmp (valp->strval, "on", sizeof ("on")) == 0)
+  if (tunable_strcmp_cte (valp, "on"))
     GL(dl_x86_feature_control).shstk = cet_always_on;
-  else if (memcmp (valp->strval, "off", sizeof ("off")) == 0)
+  else if (tunable_strcmp_cte (valp, "off"))
     GL(dl_x86_feature_control).shstk = cet_always_off;
-  else if (memcmp (valp->strval, "permissive", sizeof ("permissive")) == 0)
+  else if (tunable_strcmp_cte (valp, "permissive"))
     GL(dl_x86_feature_control).shstk = cet_permissive;
 }
 #endif