[PATCH] libm/x86: use call instead of jump for wrappers

Ed W lists at wildgooses.com
Wed Oct 20 10:32:49 UTC 2010


  I don't see this in the git master branch?  Was it rejected?  (Perhaps 
just missed?)

Thanks

Ed W


On 11/05/2010 13:42, Timo Teräs wrote:
> GCC can emit prologue/epilogue code for the functions in various
> different cases:
>   - frame pointers
>   - PIC build (to load ebx for indirect calls/jumps)
>   - forced stack smashing protection
>
> If we used jump in such cases, we'd corrupt the call stack and
> crash.
>
> Signed-off-by: Timo Teräs<timo.teras at iki.fi>
> ---
>   libm/ldouble_wrappers.c |   12 +++++++-----
>   1 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/libm/ldouble_wrappers.c b/libm/ldouble_wrappers.c
> index 7d5af90..5b424dc 100644
> --- a/libm/ldouble_wrappers.c
> +++ b/libm/ldouble_wrappers.c
> @@ -60,7 +60,9 @@ long long func##l(long double x) \
>    * The return value is returned in st(0) per ABI in both cases (returning
>    * a long double or returning a double). So we can simply jump to func.
>    * Using __GI_func in jump to make optimized intra-library jump.
> - * gcc will still generate a useless "ret" after asm. Oh well...
> + *
> + * We do need to use call (instead of tail jump) as gcc can create
> + * stack frame, and push/modify/pop ebx during PIC build.
>    */
>   # define WRAPPER1(func) \
>   long double func##l(long double x) \
> @@ -69,7 +71,7 @@ long double func##l(long double x) \
>   	__asm ( \
>   	"	fldt	%1\n" \
>   	"	fstpl	%1\n" \
> -	"	jmp	" __stringify(__GI_##func) "\n" \
> +	"	call	" __stringify(__GI_##func) "\n" \
>   	: "=t" (st_top) \
>   	: "m" (x) \
>   	); \
> @@ -82,7 +84,7 @@ int func##l(long double x) \
>   	__asm ( \
>   	"	fldt	%1\n" \
>   	"	fstpl	%1\n" \
> -	"	jmp	" __stringify(__GI_##func) "\n" \
> +	"	call	" __stringify(__GI_##func) "\n" \
>   	: "=a" (ret) \
>   	: "m" (x) \
>   	); \
> @@ -95,7 +97,7 @@ long func##l(long double x) \
>   	__asm ( \
>   	"	fldt	%1\n" \
>   	"	fstpl	%1\n" \
> -	"	jmp	" __stringify(__GI_##func) "\n" \
> +	"	call	" __stringify(__GI_##func) "\n" \
>   	: "=a" (ret) \
>   	: "m" (x) \
>   	); \
> @@ -108,7 +110,7 @@ long long func##l(long double x) \
>   	__asm ( \
>   	"	fldt	%1\n" \
>   	"	fstpl	%1\n" \
> -	"	jmp	" __stringify(__GI_##func) "\n" \
> +	"	call	" __stringify(__GI_##func) "\n" \
>   	: "=A" (ret) \
>   	: "m" (x) \
>   	); \




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