[PATCH i-g-t] lib: Inline igt_x86_features() into ifunc resolvers

[Matt Turner <mattst88@gmail.com>]

Quoting https://sourceware.org/glibc/wiki/GNU_IFUNC

> When LD_BIND_NOW=1 or -Wl,z,now is in effect symbols must be
> immediately resolved at startup. In cases where an external function
> call depends needs to be made that may fail if such a call has not
> been initialized yet (PLT-based relocation which is processed later).
> For example calling strlen in an IFUNC resolver built with -Wl,z,now
> may lead to a segfault because the PLT is not yet resolved.

We cannot rely on function calls through the PLT in ifunc resolvers as
the PLT may not have been initialized yet.

In practice, this causes crashes when igt is linked with -Wl,-z,now or
when linked with the mold linker.

To avoid this problem, we do two things:
    1. move igt_x86_features() to igt_x86.h so its definition is
       available to compilation units that call the function.
    2. mark the ifunc resolvers with __attribute__((flatten)) to ensure
       igt_x86_features() is inlined.

Bug: https://bugs.gentoo.org/788625
Bug: https://bugs.gentoo.org/925348
Signed-off-by: Matt Turner <mattst88@gmail.com>
---
 lib/igt_halffloat.c |   2 +
 lib/igt_x86.c       | 116 +------------------------------------------
 lib/igt_x86.h       | 117 +++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 119 insertions(+), 116 deletions(-)

diff --git a/lib/igt_halffloat.c b/lib/igt_halffloat.c
index 5dbe08e01..67d26c225 100644
--- a/lib/igt_halffloat.c
+++ b/lib/igt_halffloat.c
@@ -194,6 +194,7 @@ static void half_to_float(const uint16_t *h, float *f, unsigned int num)
 		f[i] = _half_to_float(h[i]);
 }
 
+__attribute__((flatten))
 static void (*resolve_float_to_half(void))(const float *f, uint16_t *h, unsigned int num)
 {
 	if (igt_x86_features() & F16C)
@@ -205,6 +206,7 @@ static void (*resolve_float_to_half(void))(const float *f, uint16_t *h, unsigned
 void igt_float_to_half(const float *f, uint16_t *h, unsigned int num)
 	__attribute__((ifunc("resolve_float_to_half")));
 
+__attribute__((flatten))
 static void (*resolve_half_to_float(void))(const uint16_t *h, float *f, unsigned int num)
 {
 	if (igt_x86_features() & F16C)
diff --git a/lib/igt_x86.c b/lib/igt_x86.c
index 8c102fd13..f103b9820 100644
--- a/lib/igt_x86.c
+++ b/lib/igt_x86.c
@@ -27,14 +27,6 @@
 
 #include "config.h"
 
-#ifdef HAVE_CPUID_H
-#include <cpuid.h>
-#else
-#define __get_cpuid_max(x, y) 0
-#define __cpuid(level, a, b, c, d) a = b = c = d = 0
-#define __cpuid_count(level, count, a, b, c, d) a = b = c = d = 0
-#endif
-
 #include "igt_x86.h"
 #include "igt_aux.h"
 
@@ -49,114 +41,7 @@
  * @include: igt_x86.h
  */
 
-#define BASIC_CPUID 0x0
-#define EXTENDED_CPUID 0x80000000
-
-#ifndef bit_MMX
-#define bit_MMX		(1 << 23)
-#endif
-
-#ifndef bit_SSE
-#define bit_SSE		(1 << 25)
-#endif
-
-#ifndef bit_SSE2
-#define bit_SSE2	(1 << 26)
-#endif
-
-#ifndef bit_SSE3
-#define bit_SSE3	(1 << 0)
-#endif
-
-#ifndef bit_SSSE3
-#define bit_SSSE3	(1 << 9)
-#endif
-
-#ifndef bit_SSE4_1
-#define bit_SSE4_1	(1 << 19)
-#endif
-
-#ifndef bit_SSE4_2
-#define bit_SSE4_2	(1 << 20)
-#endif
-
-#ifndef bit_OSXSAVE
-#define bit_OSXSAVE	(1 << 27)
-#endif
-
-#ifndef bit_AVX
-#define bit_AVX		(1 << 28)
-#endif
-
-#ifndef bit_F16C
-#define bit_F16C	(1 << 29)
-#endif
-
-#ifndef bit_AVX2
-#define bit_AVX2	(1<<5)
-#endif
-
-#define xgetbv(index,eax,edx) \
-	__asm__ ("xgetbv" : "=a"(eax), "=d"(edx) : "c" (index))
-
-#define has_YMM 0x1
-
 #if defined(__x86_64__) || defined(__i386__)
-unsigned igt_x86_features(void)
-{
-	unsigned max = __get_cpuid_max(BASIC_CPUID, 0);
-	unsigned eax, ebx, ecx, edx;
-	unsigned features = 0;
-	unsigned extra = 0;
-
-	if (max >= 1) {
-		__cpuid(1, eax, ebx, ecx, edx);
-
-		if (ecx & bit_SSE3)
-			features |= SSE3;
-
-		if (ecx & bit_SSSE3)
-			features |= SSSE3;
-
-		if (ecx & bit_SSE4_1)
-			features |= SSE4_1;
-
-		if (ecx & bit_SSE4_2)
-			features |= SSE4_2;
-
-		if (ecx & bit_OSXSAVE) {
-			unsigned int bv_eax, bv_ecx;
-			xgetbv(0, bv_eax, bv_ecx);
-			if ((bv_eax & 6) == 6)
-				extra |= has_YMM;
-		}
-
-		if ((extra & has_YMM) && (ecx & bit_AVX))
-			features |= AVX;
-
-		if (edx & bit_MMX)
-			features |= MMX;
-
-		if (edx & bit_SSE)
-			features |= SSE;
-
-		if (edx & bit_SSE2)
-			features |= SSE2;
-
-		if (ecx & bit_F16C)
-			features |= F16C;
-	}
-
-	if (max >= 7) {
-		__cpuid_count(7, 0, eax, ebx, ecx, edx);
-
-		if ((extra & has_YMM) && (ebx & bit_AVX2))
-			features |= AVX2;
-	}
-
-	return features;
-}
-
 char *igt_x86_features_to_string(unsigned features, char *line)
 {
 	char *ret = line;
@@ -284,6 +169,7 @@ static void memcpy_from_wc(void *dst, const void *src, unsigned long len)
 	memcpy(dst, src, len);
 }
 
+__attribute__((flatten))
 static void (*resolve_memcpy_from_wc(void))(void *, const void *, unsigned long)
 {
 	if (igt_x86_features() & SSE4_1)
diff --git a/lib/igt_x86.h b/lib/igt_x86.h
index c7b84dec2..1e0195c4b 100644
--- a/lib/igt_x86.h
+++ b/lib/igt_x86.h
@@ -30,6 +30,14 @@
 #ifndef IGT_X86_H
 #define IGT_X86_H
 
+#ifdef HAVE_CPUID_H
+#include <cpuid.h>
+#else
+#define __get_cpuid_max(x, y) 0
+#define __cpuid(level, a, b, c, d) a = b = c = d = 0
+#define __cpuid_count(level, count, a, b, c, d) a = b = c = d = 0
+#endif
+
 #define MMX	0x1
 #define SSE	0x2
 #define SSE2	0x4
@@ -42,7 +50,114 @@
 #define F16C	0x200
 
 #if defined(__x86_64__) || defined(__i386__)
-unsigned igt_x86_features(void);
+
+#define BASIC_CPUID 0x0
+#define EXTENDED_CPUID 0x80000000
+
+#ifndef bit_MMX
+#define bit_MMX		(1 << 23)
+#endif
+
+#ifndef bit_SSE
+#define bit_SSE		(1 << 25)
+#endif
+
+#ifndef bit_SSE2
+#define bit_SSE2	(1 << 26)
+#endif
+
+#ifndef bit_SSE3
+#define bit_SSE3	(1 << 0)
+#endif
+
+#ifndef bit_SSSE3
+#define bit_SSSE3	(1 << 9)
+#endif
+
+#ifndef bit_SSE4_1
+#define bit_SSE4_1	(1 << 19)
+#endif
+
+#ifndef bit_SSE4_2
+#define bit_SSE4_2	(1 << 20)
+#endif
+
+#ifndef bit_OSXSAVE
+#define bit_OSXSAVE	(1 << 27)
+#endif
+
+#ifndef bit_AVX
+#define bit_AVX		(1 << 28)
+#endif
+
+#ifndef bit_F16C
+#define bit_F16C	(1 << 29)
+#endif
+
+#ifndef bit_AVX2
+#define bit_AVX2	(1<<5)
+#endif
+
+#define xgetbv(index,eax,edx) \
+	__asm__ ("xgetbv" : "=a"(eax), "=d"(edx) : "c" (index))
+
+#define has_YMM 0x1
+
+static inline unsigned igt_x86_features(void)
+{
+	unsigned max = __get_cpuid_max(BASIC_CPUID, 0);
+	unsigned eax, ebx, ecx, edx;
+	unsigned features = 0;
+	unsigned extra = 0;
+
+	if (max >= 1) {
+		__cpuid(1, eax, ebx, ecx, edx);
+
+		if (ecx & bit_SSE3)
+			features |= SSE3;
+
+		if (ecx & bit_SSSE3)
+			features |= SSSE3;
+
+		if (ecx & bit_SSE4_1)
+			features |= SSE4_1;
+
+		if (ecx & bit_SSE4_2)
+			features |= SSE4_2;
+
+		if (ecx & bit_OSXSAVE) {
+			unsigned int bv_eax, bv_ecx;
+			xgetbv(0, bv_eax, bv_ecx);
+			if ((bv_eax & 6) == 6)
+				extra |= has_YMM;
+		}
+
+		if ((extra & has_YMM) && (ecx & bit_AVX))
+			features |= AVX;
+
+		if (edx & bit_MMX)
+			features |= MMX;
+
+		if (edx & bit_SSE)
+			features |= SSE;
+
+		if (edx & bit_SSE2)
+			features |= SSE2;
+
+		if (ecx & bit_F16C)
+			features |= F16C;
+	}
+
+	if (max >= 7) {
+		__cpuid_count(7, 0, eax, ebx, ecx, edx);
+
+		if ((extra & has_YMM) && (ebx & bit_AVX2))
+			features |= AVX2;
+	}
+
+	return features;
+}
+
 char *igt_x86_features_to_string(unsigned features, char *line);
 #else
 static inline unsigned igt_x86_features(void)
-- 
2.43.0