Re: [PATCH V3] vDSO for SPARC

[nagarathnam muthusamy <nagarathnam.muthusamy@oracle.com>]

Hi David,
     I have fixed the issues with the patch and sent an updated patch. I 
was able to reproduce the issue
in a qemu sparc emulator running Debian. I checked that the VDSO 
binaries pass compilation with the
new patch in that environment.

Thanks,
Nagarathnam.
On 9/10/2017 9:03 PM, David Miller wrote:
> From: David Miller <davem@davemloft.net>
> Date: Sat, 09 Sep 2017 20:41:29 -0700 (PDT)
>
>> The arch/sparc/vdso/vdso.lds file says:
>>
>> vvar_start = . -(1 << 12);
>>
>> And "1 << 12" is 4096, therefore a multiple of 4096 and not 8192.
>>
>> So, as requested, the object built gets:
>>
>> davem@patience:~/src/GIT/sparc-next$ nm -n arch/sparc/vdso/vdso64.so.dbg
>> fffffffffffff000 a vvar_data
>> fffffffffffff000 a vvar_start
> Breaking this down further, the linker scripts are written assuming
> they will be built by a host compiler that generates 64-bit target
> code by default.
>
> This is not a safe assumption.
>
> My system generates 32-bit binaries from gcc by default, and that's
> why you end up with a value of PAGE_SIZE which is 4096 propagating
> through all of the generated linker scripts.
>
> x86, where it seems like were at least used as a template for the
> sparc linker scripts, gets away with this because the PAGE_SIZE
> is the same on 32-bit and 64-bit.
>
> Anyways, since 8192 is hard coded into vdso2c, just use 8192 as
> PAGE_SIZE in vdso-layout.lds.S and maybe put a comment above it.
>
> The next problem with the patch is that we get a warning because
> the variable 'secstrings_hdr' is set but not used in vdso2c.h, and
> compiler warnings are treated as errors under arch/sparc.
>
> This is fixed simply by:
>
> diff --git a/arch/sparc/vdso/vdso2c.h b/arch/sparc/vdso/vdso2c.h
> index 8d1b5cf..b193e3d 100644
> --- a/arch/sparc/vdso/vdso2c.h
> +++ b/arch/sparc/vdso/vdso2c.h
> @@ -17,9 +17,8 @@ static void BITSFUNC(go)(void *raw_addr, size_t raw_len,
>   	unsigned long mapping_size;
>   	int i;
>   	unsigned long j;
> -	const char *secstrings;
>   
> -	ELF(Shdr) *symtab_hdr = NULL, *strtab_hdr, *secstrings_hdr;
> +	ELF(Shdr) *symtab_hdr = NULL, *strtab_hdr;
>   	ELF(Ehdr) *hdr = (ELF(Ehdr) *)raw_addr;
>   	ELF(Dyn) *dyn = 0, *dyn_end = 0;
>   	INT_BITS syms[NSYMS] = {};
> @@ -64,9 +63,6 @@ static void BITSFUNC(go)(void *raw_addr, size_t raw_len,
>   	}
>   
>   	/* Walk the section table */
> -	secstrings_hdr = raw_addr + GET_BE(&hdr->e_shoff) +
> -		GET_BE(&hdr->e_shentsize)*GET_BE(&hdr->e_shstrndx);
> -	secstrings = raw_addr + GET_BE(&secstrings_hdr->sh_offset);
>   	for (i = 0; i < GET_BE(&hdr->e_shnum); i++) {
>   		ELF(Shdr) *sh = raw_addr + GET_BE(&hdr->e_shoff) +
>   			GET_BE(&hdr->e_shentsize) * i;