[igt-dev] [PATCH i-g-t] Fix global symbol loading failure in resolve function

[Ville Syrjälä]

On Tue, Sep 24, 2019 at 10:02:29PM +0800, brandon.hong at intel.com wrote:
> From: Brandon Hong <brandon.hong at intel.com>
> 
> 270 out of 284 tests get failed with SIGSEGV on ClearLinux because the ifunc
> resolver resolve_half_to_float() tries to call unbound global function
> igt_x86_features(). This patch fixes the issue by adding a F16C checking
> local function.

The rules for this stuff seem to be poorly documented. But I did find
some docs that support this. So generally lgtm, just a few nitpicks
below...

> 
> Signed-off-by: Brandon Hong <brandon.hong at intel.com>
> ---
>  lib/igt_halffloat.c | 22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/igt_halffloat.c b/lib/igt_halffloat.c
> index 08ab05fc..fa7ad2e0 100644
> --- a/lib/igt_halffloat.c
> +++ b/lib/igt_halffloat.c
> @@ -24,6 +24,7 @@
>  
>  #include <assert.h>
>  #include <math.h>
> +#include <stdbool.h>
>  
>  #include "igt_halffloat.h"
>  #include "igt_x86.h"
> @@ -163,6 +164,8 @@ static inline float _half_to_float(uint16_t val)
>  }
>  
>  #if defined(__x86_64__) && !defined(__clang__)
> +#include <cpuid.h>

igt_x86.c has HAVE_CPUID_H protection around this stuff.
I suppose we'd want the same here?

> +
>  #pragma GCC push_options
>  #pragma GCC target("f16c")
>  
> @@ -182,6 +185,20 @@ static void half_to_float_f16c(const uint16_t *h, float *f, unsigned int num)
>  
>  #pragma GCC pop_options
>  
> +static bool f16c_is_supported(void)
> +{
> +	unsigned max = __get_cpuid_max(0, NULL);
> +	unsigned eax, ebx, ecx, edx;
> +
> +	if (max >= 1) {
> +		__cpuid(1, eax, ebx, ecx, edx);
> +
> +		if (ecx & bit_F16C)
> +			return true;
> +	}
> +	return false;
> +}
> +
>  static void float_to_half(const float *f, uint16_t *h, unsigned int num)
>  {
>  	for (int i = 0; i < num; i++)
> @@ -194,9 +211,10 @@ static void half_to_float(const uint16_t *h, float *f, unsigned int num)
>  		f[i] = _half_to_float(h[i]);
>  }
>  
> +

Spurious newline.

>  static void (*resolve_float_to_half(void))(const float *f, uint16_t *h, unsigned int num)
>  {
> -	if (igt_x86_features() & F16C)
> +	if (f16c_is_supported())
>  		return float_to_half_f16c;
>  
>  	return float_to_half;
> @@ -207,7 +225,7 @@ void igt_float_to_half(const float *f, uint16_t *h, unsigned int num)
>  
>  static void (*resolve_half_to_float(void))(const uint16_t *h, float *f, unsigned int num)
>  {
> -	if (igt_x86_features() & F16C)
> +	if (f16c_is_supported())
>  		return half_to_float_f16c;
>  
>  	return half_to_float;
> -- 
> 2.23.0
> 
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-- 
Ville Syrjälä
Intel