linux-kernel - Re: [PATCH v5 17/23] arm64:ilp32: add vdso-ilp32 and use for signal return

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Message-ID: <560B5FB5.6080605@mentor.com>
Date:	Tue, 29 Sep 2015 23:06:13 -0500
From:	Nathan Lynch <Nathan_Lynch@...tor.com>
To:	Yury Norov <ynorov@...iumnetworks.com>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <catalin.marinas@....com>,
	<arnd@...db.de>, <agraf@...e.de>, <bamvor.zhangjian@...wei.com>,
	<yury.norov@...il.com>, <klimov.linux@...il.com>,
	<apinski@...ium.com>, <philipp.tomsich@...obroma-systems.com>,
	<christoph.muellner@...obroma-systems.com>
Subject: Re: [PATCH v5 17/23] arm64:ilp32: add vdso-ilp32 and use for signal
 return

On 09/29/2015 05:14 PM, Yury Norov wrote:
> From: Philipp Tomsich <philipp.tomsich@...obroma-systems.com>
> 
> Adjusted to move the move data page before code pages in sync with
> commit 601255ae3c98fdeeee3a8bb4696425e4f868b4f1

This commit message needs more information about how the ilp32 VDSO uses
the existing arm64 code.  I had to really hunt through the Makefile to
figure out what's going on.

The commit message should also identify the APIs that are supported.
The subject line mentions signal return, but gettimeofday, clock_gettime
and clock_getres are being added here too, and it is not obvious.


> Signed-off-by: Philipp Tomsich <philipp.tomsich@...obroma-systems.com>
> Signed-off-by: Christoph Muellner <christoph.muellner@...obroma-systems.com>
> Signed-off-by: Yury Norov <ynorov@...iumnetworks.com>
> 
>  create mode 100644 arch/arm64/kernel/vdso-ilp32/.gitignore
>  create mode 100644 arch/arm64/kernel/vdso-ilp32/Makefile
>  copy arch/arm64/{include/asm/vdso.h => kernel/vdso-ilp32/vdso-ilp32.S} (56%)
>  create mode 100644 arch/arm64/kernel/vdso-ilp32/vdso-ilp32.lds.S

How are you invoking git-format-patch?  The copy detection in this case
is not conducive to review.

It looks like the existing arm64 vdso Makefile has been copied to
vdso-ilp32/ and adjusted for paths and naming.  While the gettimeofday
assembly implementation is reused, the build logic is duplicated.  x86
produces VDSOs for multiple ABIs with a single Makefile; is a similar
approach not appropriate for arm64?


> diff --git a/arch/arm64/kernel/vdso-ilp32/vdso-ilp32.lds.S b/arch/arm64/kernel/vdso-ilp32/vdso-ilp32.lds.S
> new file mode 100644
> index 0000000..ac8029b
> --- /dev/null
> +++ b/arch/arm64/kernel/vdso-ilp32/vdso-ilp32.lds.S
> @@ -0,0 +1,98 @@

[...]

> +#include <linux/const.h>
> +#include <asm/page.h>
> +#include <asm/vdso.h>
> +
> +/*OUTPUT_FORMAT("elf32-littleaarch64", "elf32-bigaarch64", "elf32-littleaarch64")
> +OUTPUT_ARCH(aarch64)
> +*/

If these lines aren't needed then omit them.

[...]


> +/*
> + * This controls what symbols we export from the DSO.
> + */
> +VERSION
> +{
> +	LINUX_2.6.39 {
> +	global:
> +		__kernel_rt_sigreturn;
> +		__kernel_gettimeofday;
> +		__kernel_clock_gettime;
> +		__kernel_clock_getres;
> +	local: *;
> +	};
> +}

Something that came up during review of arch/arm's VDSO code: consider
using version and names that match x86, i.e. LINUX_2.6, __vdso_gettimeofday.

http://lists.infradead.org/pipermail/linux-arm-kernel/2014-June/267940.html

Using LINUX_2.6.39 for this code is nonsensical.


> diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
> index b239b9b..bed6cf1 100644
> --- a/arch/arm64/kernel/vdso.c
> +++ b/arch/arm64/kernel/vdso.c
> @@ -40,6 +40,12 @@ extern char vdso_start, vdso_end;
>  static unsigned long vdso_pages;
>  static struct page **vdso_pagelist;
>  
> +#ifdef CONFIG_ARM64_ILP32
> +extern char vdso_ilp32_start, vdso_ilp32_end;
> +static unsigned long vdso_ilp32_pages;
> +static struct page **vdso_ilp32_pagelist;
> +#endif
> +
>  /*
>   * The vDSO data page.
>   */
> @@ -117,24 +123,29 @@ int aarch32_setup_vectors_page(struct linux_binprm *bprm, int uses_interp)
>  }
>  #endif /* CONFIG_AARCH32_EL0 */
>  
> -static struct vm_special_mapping vdso_spec[2];
> -
> -static int __init vdso_init(void)
> +static inline int __init vdso_init_common(char *vdso_start, char *vdso_end,

No inline please.


> +					  unsigned long *vdso_pagesp,
> +					  struct page ***vdso_pagelistp,
> +					  struct vm_special_mapping* vdso_spec)
>  {

[...]

>  int arch_setup_additional_pages(struct linux_binprm *bprm,
>  				int uses_interp)
>  {
>  	struct mm_struct *mm = current->mm;
>  	unsigned long vdso_base, vdso_text_len, vdso_mapping_len;
> -	void *ret;
> +	void* ret;

Gratuitous (and incorrect) style change.


> +	unsigned long pages = vdso_pages;
> +	struct vm_special_mapping* spec = vdso_spec;

Incorrect style:                  *spec

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