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* [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations
@ 2018-05-16 14:20 Dave Martin
  2018-05-16 15:29 ` Rich Felker
                   ` (2 more replies)
  0 siblings, 3 replies; 7+ messages in thread
From: Dave Martin @ 2018-05-16 14:20 UTC (permalink / raw)
  To: linux-kernel
  Cc: x86, linux-arch, linux-api, Richard Henderson, Ivan Kokshaysky,
	Matt Turner, Russell King, Catalin Marinas, Will Deacon,
	Tony Luck, Fenghua Yu, Michal Simek, Ralf Baechle, James Hogan,
	Greentime Hu, Vincent Chen, Benjamin Herrenschmidt,
	Paul Mackerras, Michael Ellerman, Palmer Dabbelt, Albert Ou,
	Martin Schwidefsky, Heiko Carstens, Yoshinori Sato, Rich Felker,
	David S. Miller, Thomas Gleixner, Ingo Molnar, H. Peter Anvin,
	Chris Zankel, Max Filippov

There are constraints on defining AT_* auxvec tags that are not
obvious to the casual maintainer of either the global
<uapi/linux/auxvec.h> or the arch-specific headers.  This is likely
to lead to mistakes.  (I certainly fell foul of it...)

For the benefit of future maintainers, this patch collects the
relevant information in one place, documenting how the namespace
needs to be managed, and noting all the values currently in use.

Maintaining a global list may result in some merge conflicts, but
AT_* values are not added frequently.  I'm open to suggestions on
the best approach.

I also assume that values 38 and 39 may have been used for
historical purposes, such as an architecture that is no longer
supported.  If they have definitely never been used for anything,
they could be removed from the "reserved" list.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Greentime Hu <green.hu@gmail.com>
Cc: Vincent Chen <deanbo422@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Albert Ou <albert@sifive.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
---
 arch/alpha/include/uapi/asm/auxvec.h      |  5 ++++
 arch/arm/include/uapi/asm/auxvec.h        |  5 ++++
 arch/arm64/include/uapi/asm/auxvec.h      |  5 ++++
 arch/ia64/include/uapi/asm/auxvec.h       |  5 ++++
 arch/microblaze/include/uapi/asm/auxvec.h |  4 ++++
 arch/mips/include/uapi/asm/auxvec.h       |  5 ++++
 arch/nds32/include/uapi/asm/auxvec.h      |  5 ++++
 arch/powerpc/include/uapi/asm/auxvec.h    |  5 ++++
 arch/riscv/include/uapi/asm/auxvec.h      |  5 ++++
 arch/s390/include/uapi/asm/auxvec.h       |  5 ++++
 arch/sh/include/uapi/asm/auxvec.h         |  5 ++++
 arch/sparc/include/uapi/asm/auxvec.h      |  8 ++++---
 arch/x86/include/uapi/asm/auxvec.h        |  5 ++++
 arch/xtensa/include/uapi/asm/auxvec.h     |  5 ++++
 include/uapi/linux/auxvec.h               | 40 ++++++++++++++++++++++++++++---
 15 files changed, 106 insertions(+), 6 deletions(-)

diff --git a/arch/alpha/include/uapi/asm/auxvec.h b/arch/alpha/include/uapi/asm/auxvec.h
index 57cae87..9370d78 100644
--- a/arch/alpha/include/uapi/asm/auxvec.h
+++ b/arch/alpha/include/uapi/asm/auxvec.h
@@ -22,6 +22,11 @@
 #define AT_L2_CACHESHAPE	36
 #define AT_L3_CACHESHAPE	37
 
+/*
+ * Do not add new AT_* definitions here without coordinating with
+ * <uapi/linux/auxvec.h>
+ */
+
 #define AT_VECTOR_SIZE_ARCH 4 /* entries in ARCH_DLINFO */
 
 #endif /* __ASM_ALPHA_AUXVEC_H */
diff --git a/arch/arm/include/uapi/asm/auxvec.h b/arch/arm/include/uapi/asm/auxvec.h
index 5c09da5..b5cfba2 100644
--- a/arch/arm/include/uapi/asm/auxvec.h
+++ b/arch/arm/include/uapi/asm/auxvec.h
@@ -5,4 +5,9 @@
 /* VDSO location */
 #define AT_SYSINFO_EHDR	33
 
+/*
+ * Do not add new AT_* definitions here without coordinating with
+ * <uapi/linux/auxvec.h>
+ */
+
 #endif
diff --git a/arch/arm64/include/uapi/asm/auxvec.h b/arch/arm64/include/uapi/asm/auxvec.h
index ec0a86d..3da03fc 100644
--- a/arch/arm64/include/uapi/asm/auxvec.h
+++ b/arch/arm64/include/uapi/asm/auxvec.h
@@ -20,6 +20,11 @@
 /* vDSO location */
 #define AT_SYSINFO_EHDR	33
 
+/*
+ * Do not add new AT_* definitions here without coordinating with
+ * <uapi/linux/auxvec.h>
+ */
+
 #define AT_VECTOR_SIZE_ARCH 1 /* entries in ARCH_DLINFO */
 
 #endif
diff --git a/arch/ia64/include/uapi/asm/auxvec.h b/arch/ia64/include/uapi/asm/auxvec.h
index 09969a5..a81aec5 100644
--- a/arch/ia64/include/uapi/asm/auxvec.h
+++ b/arch/ia64/include/uapi/asm/auxvec.h
@@ -9,6 +9,11 @@
 #define AT_SYSINFO	32
 #define AT_SYSINFO_EHDR	33
 
+/*
+ * Do not add new AT_* definitions here without coordinating with
+ * <uapi/linux/auxvec.h>
+ */
+
 #define AT_VECTOR_SIZE_ARCH 2 /* entries in ARCH_DLINFO */
 
 #endif /* _ASM_IA64_AUXVEC_H */
diff --git a/arch/microblaze/include/uapi/asm/auxvec.h b/arch/microblaze/include/uapi/asm/auxvec.h
index 93dd07b..b08c6dc 100644
--- a/arch/microblaze/include/uapi/asm/auxvec.h
+++ b/arch/microblaze/include/uapi/asm/auxvec.h
@@ -1,2 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
 
+/*
+ * Do not add new AT_* definitions here without coordinating with
+ * <uapi/linux/auxvec.h>
+ */
diff --git a/arch/mips/include/uapi/asm/auxvec.h b/arch/mips/include/uapi/asm/auxvec.h
index 612c2c4..ee94899 100644
--- a/arch/mips/include/uapi/asm/auxvec.h
+++ b/arch/mips/include/uapi/asm/auxvec.h
@@ -15,6 +15,11 @@
 /* Location of VDSO image. */
 #define AT_SYSINFO_EHDR		33
 
+/*
+ * Do not add new AT_* definitions here without coordinating with
+ * <uapi/linux/auxvec.h>
+ */
+
 #define AT_VECTOR_SIZE_ARCH 1 /* entries in ARCH_DLINFO */
 
 #endif /* __ASM_AUXVEC_H */
diff --git a/arch/nds32/include/uapi/asm/auxvec.h b/arch/nds32/include/uapi/asm/auxvec.h
index 56043ce..0173da1 100644
--- a/arch/nds32/include/uapi/asm/auxvec.h
+++ b/arch/nds32/include/uapi/asm/auxvec.h
@@ -7,6 +7,11 @@
 /* VDSO location */
 #define AT_SYSINFO_EHDR	33
 
+/*
+ * Do not add new AT_* definitions here without coordinating with
+ * <uapi/linux/auxvec.h>
+ */
+
 #define AT_VECTOR_SIZE_ARCH 1
 
 #endif
diff --git a/arch/powerpc/include/uapi/asm/auxvec.h b/arch/powerpc/include/uapi/asm/auxvec.h
index 7af21dc..3da0713 100644
--- a/arch/powerpc/include/uapi/asm/auxvec.h
+++ b/arch/powerpc/include/uapi/asm/auxvec.h
@@ -48,6 +48,11 @@
 #define AT_L3_CACHESIZE		46
 #define AT_L3_CACHEGEOMETRY	47
 
+/*
+ * Do not add new AT_* definitions here without coordinating with
+ * <uapi/linux/auxvec.h>
+ */
+
 #define AT_VECTOR_SIZE_ARCH	14 /* entries in ARCH_DLINFO */
 
 #endif
diff --git a/arch/riscv/include/uapi/asm/auxvec.h b/arch/riscv/include/uapi/asm/auxvec.h
index 1376515..0dd7983 100644
--- a/arch/riscv/include/uapi/asm/auxvec.h
+++ b/arch/riscv/include/uapi/asm/auxvec.h
@@ -21,4 +21,9 @@
 /* vDSO location */
 #define AT_SYSINFO_EHDR 33
 
+/*
+ * Do not add new AT_* definitions here without coordinating with
+ * <uapi/linux/auxvec.h>
+ */
+
 #endif /* _UAPI_ASM_RISCV_AUXVEC_H */
diff --git a/arch/s390/include/uapi/asm/auxvec.h b/arch/s390/include/uapi/asm/auxvec.h
index a056c46..c30090a 100644
--- a/arch/s390/include/uapi/asm/auxvec.h
+++ b/arch/s390/include/uapi/asm/auxvec.h
@@ -4,6 +4,11 @@
 
 #define AT_SYSINFO_EHDR		33
 
+/*
+ * Do not add new AT_* definitions here without coordinating with
+ * <uapi/linux/auxvec.h>
+ */
+
 #define AT_VECTOR_SIZE_ARCH 1 /* entries in ARCH_DLINFO */
 
 #endif
diff --git a/arch/sh/include/uapi/asm/auxvec.h b/arch/sh/include/uapi/asm/auxvec.h
index 8eb47ed..e5b6ebc 100644
--- a/arch/sh/include/uapi/asm/auxvec.h
+++ b/arch/sh/include/uapi/asm/auxvec.h
@@ -34,6 +34,11 @@
 #define AT_L1D_CACHESHAPE	35
 #define AT_L2_CACHESHAPE	36
 
+/*
+ * Do not add new AT_* definitions here without coordinating with
+ * <uapi/linux/auxvec.h>
+ */
+
 #define AT_VECTOR_SIZE_ARCH 5 /* entries in ARCH_DLINFO */
 
 #endif /* __ASM_SH_AUXVEC_H */
diff --git a/arch/sparc/include/uapi/asm/auxvec.h b/arch/sparc/include/uapi/asm/auxvec.h
index ab8780f..76aba18 100644
--- a/arch/sparc/include/uapi/asm/auxvec.h
+++ b/arch/sparc/include/uapi/asm/auxvec.h
@@ -3,13 +3,15 @@
 
 #define AT_SYSINFO_EHDR		33
 
-/* Avoid overlap with other AT_* values since they are consolidated in
- * glibc and any overlaps can cause problems
- */
 #define AT_ADI_BLKSZ	48
 #define AT_ADI_NBITS	49
 #define AT_ADI_UEONADI	50
 
+/*
+ * Do not add new AT_* definitions here without coordinating with
+ * <uapi/linux/auxvec.h>
+ */
+
 #define AT_VECTOR_SIZE_ARCH	4
 
 #endif /* !(__ASMSPARC_AUXVEC_H) */
diff --git a/arch/x86/include/uapi/asm/auxvec.h b/arch/x86/include/uapi/asm/auxvec.h
index 580e3c5..700c0fc 100644
--- a/arch/x86/include/uapi/asm/auxvec.h
+++ b/arch/x86/include/uapi/asm/auxvec.h
@@ -10,6 +10,11 @@
 #endif
 #define AT_SYSINFO_EHDR		33
 
+/*
+ * Do not add new AT_* definitions here without coordinating with
+ * <uapi/linux/auxvec.h>
+ */
+
 /* entries in ARCH_DLINFO: */
 #if defined(CONFIG_IA32_EMULATION) || !defined(CONFIG_X86_64)
 # define AT_VECTOR_SIZE_ARCH 2
diff --git a/arch/xtensa/include/uapi/asm/auxvec.h b/arch/xtensa/include/uapi/asm/auxvec.h
index 257dec7..995bbd8 100644
--- a/arch/xtensa/include/uapi/asm/auxvec.h
+++ b/arch/xtensa/include/uapi/asm/auxvec.h
@@ -1,4 +1,9 @@
 #ifndef __XTENSA_AUXVEC_H
 #define __XTENSA_AUXVEC_H
 
+/*
+ * Do not add new AT_* definitions here without coordinating with
+ * <uapi/linux/auxvec.h>
+ */
+
 #endif
diff --git a/include/uapi/linux/auxvec.h b/include/uapi/linux/auxvec.h
index abe5f2b..c19c043 100644
--- a/include/uapi/linux/auxvec.h
+++ b/include/uapi/linux/auxvec.h
@@ -4,8 +4,19 @@
 
 #include <asm/auxvec.h>
 
-/* Symbolic values for the entries in the auxiliary table
-   put on the initial stack */
+/*
+ * Symbolic values for the entries in the auxiliary table
+ * put on the initial stack.
+ *
+ * Values with definitions here are common to all architectures.
+ * Individual architectures may define additional values in their
+ * <uapi/asm/auxvec.h>.
+ *
+ * NOTE: Userspace may treat these numbers as a global namespace.
+ * Any per-architecture definition must not overlap with these or with
+ * any other architecture's definitions, unless it has identical name
+ * and number and compatible meaning.
+ */
 #define AT_NULL   0	/* end of vector */
 #define AT_IGNORE 1	/* entry should be ignored */
 #define AT_EXECFD 2	/* file descriptor of program */
@@ -24,7 +35,11 @@
 #define AT_PLATFORM 15  /* string identifying CPU for optimizations */
 #define AT_HWCAP  16    /* arch dependent hints at CPU capabilities */
 #define AT_CLKTCK 17	/* frequency at which times() increments */
-/* AT_* values 18 through 22 are reserved */
+/* 18 reserved for AT_FPUCW		(sh) */
+/* 19 reserved for AT_DCACHEBSIZE	(powerpc) */
+/* 20 reserved for AT_ICACHEBSIZE	(powerpc) */
+/* 21 reserved for AT_UCACHEBSIZE	(powerpc) */
+/* 22 reserved for AT_IGNOREPPC		(powerpc) */
 #define AT_SECURE 23   /* secure mode boolean */
 #define AT_BASE_PLATFORM 24	/* string identifying real platform, may
 				 * differ from AT_PLATFORM. */
@@ -33,5 +48,24 @@
 
 #define AT_EXECFN  31	/* filename of program */
 
+/* 32 reserved for AT_SYSINFO		(alpha ia64 um x86) */
+/* 33 reserved for AT_SYSINFO_EHDR	(various architectures) */
+/* 34 reserved for AT_L1I_CACHESHAPE	(alpha sh) */
+/* 35 reserved for AT_L1D_CACHESHAPE	(alpha sh) */
+/* 36 reserved for AT_L2_CACHESHAPE	(alpha sh) */
+/* 37 reserved for AT_L3_CACHESHAPE	(alpha) */
+/* 38 reserved, do not allocate */
+/* 39 reserved, do not allocate */
+/* 40 reserved for AT_L1I_CACHESIZE	(powerpc) */
+/* 41 reserved for AT_L1I_CACHEGEOMETRY	(powerpc) */
+/* 42 reserved for AT_L1D_CACHESIZE	(powerpc) */
+/* 43 reserved for AT_L1D_CACHEGEOMETRY	(powerpc) */
+/* 44 reserved for AT_L2_CACHESIZE	(powerpc) */
+/* 45 reserved for AT_L2_CACHEGEOMETRY	(powerpc) */
+/* 46 reserved for AT_L3_CACHESIZE	(powerpc) */
+/* 47 reserved for AT_L3_CACHEGEOMETRY	(powerpc) */
+/* 48 reserved for AT_ADI_BLKSZ		(sparc) */
+/* 49 reserved for AT_ADI_NBITS		(sparc) */
+/* 50 reserved for AT_ADI_UEONADI	(sparc) */
 
 #endif /* _UAPI_LINUX_AUXVEC_H */
-- 
2.1.4


^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations
  2018-05-16 14:20 [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations Dave Martin
@ 2018-05-16 15:29 ` Rich Felker
  2018-05-16 15:49   ` Dave Martin
  2018-05-17  6:40 ` Michael Ellerman
  2018-05-17 16:00 ` Yann Droneaud
  2 siblings, 1 reply; 7+ messages in thread
From: Rich Felker @ 2018-05-16 15:29 UTC (permalink / raw)
  To: Dave Martin
  Cc: linux-kernel, x86, linux-arch, linux-api, Richard Henderson,
	Ivan Kokshaysky, Matt Turner, Russell King, Catalin Marinas,
	Will Deacon, Tony Luck, Fenghua Yu, Michal Simek, Ralf Baechle,
	James Hogan, Greentime Hu, Vincent Chen, Benjamin Herrenschmidt,
	Paul Mackerras, Michael Ellerman, Palmer Dabbelt, Albert Ou,
	Martin Schwidefsky, Heiko Carstens, Yoshinori Sato,
	David S. Miller, Thomas Gleixner, Ingo Molnar, H. Peter Anvin,
	Chris Zankel, Max Filippov

On Wed, May 16, 2018 at 03:20:47PM +0100, Dave Martin wrote:
> There are constraints on defining AT_* auxvec tags that are not
> obvious to the casual maintainer of either the global
> <uapi/linux/auxvec.h> or the arch-specific headers.  This is likely
> to lead to mistakes.  (I certainly fell foul of it...)
> 
> For the benefit of future maintainers, this patch collects the
> relevant information in one place, documenting how the namespace
> needs to be managed, and noting all the values currently in use.
> 
> Maintaining a global list may result in some merge conflicts, but
> AT_* values are not added frequently.  I'm open to suggestions on
> the best approach.
> 
> I also assume that values 38 and 39 may have been used for
> historical purposes, such as an architecture that is no longer
> supported.  If they have definitely never been used for anything,
> they could be removed from the "reserved" list.

On the userspace side (elf.h) all the AT_* constants are in one file.
Why don't we just do the same here and eliminate the
arch/*/include/uapi/asm/auxvec.h files and likewise the need to
manually maintain consistency of the comments about reservations?

If there are reasons not to do that, I'm not opposed to this patch
as-is.

Rich

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations
  2018-05-16 15:29 ` Rich Felker
@ 2018-05-16 15:49   ` Dave Martin
  2018-05-16 23:09     ` H. Peter Anvin
  0 siblings, 1 reply; 7+ messages in thread
From: Dave Martin @ 2018-05-16 15:49 UTC (permalink / raw)
  To: Rich Felker
  Cc: linux-kernel, x86, linux-arch, linux-api, Richard Henderson,
	Ivan Kokshaysky, Matt Turner, Russell King, Catalin Marinas,
	Will Deacon, Tony Luck, Fenghua Yu, Michal Simek, Ralf Baechle,
	James Hogan, Greentime Hu, Vincent Chen, Benjamin Herrenschmidt,
	Paul Mackerras, Michael Ellerman, Palmer Dabbelt, Albert Ou,
	Martin Schwidefsky, Heiko Carstens, Yoshinori Sato,
	David S. Miller, Thomas Gleixner, Ingo Molnar, H. Peter Anvin,
	Chris Zankel, Max Filippov

On Wed, May 16, 2018 at 11:29:13AM -0400, Rich Felker wrote:
> On Wed, May 16, 2018 at 03:20:47PM +0100, Dave Martin wrote:
> > There are constraints on defining AT_* auxvec tags that are not
> > obvious to the casual maintainer of either the global
> > <uapi/linux/auxvec.h> or the arch-specific headers.  This is likely
> > to lead to mistakes.  (I certainly fell foul of it...)
> > 
> > For the benefit of future maintainers, this patch collects the
> > relevant information in one place, documenting how the namespace
> > needs to be managed, and noting all the values currently in use.
> > 
> > Maintaining a global list may result in some merge conflicts, but
> > AT_* values are not added frequently.  I'm open to suggestions on
> > the best approach.
> > 
> > I also assume that values 38 and 39 may have been used for
> > historical purposes, such as an architecture that is no longer
> > supported.  If they have definitely never been used for anything,
> > they could be removed from the "reserved" list.
> 
> On the userspace side (elf.h) all the AT_* constants are in one file.
> Why don't we just do the same here and eliminate the
> arch/*/include/uapi/asm/auxvec.h files and likewise the need to
> manually maintain consistency of the comments about reservations?
> 
> If there are reasons not to do that, I'm not opposed to this patch
> as-is.

I agree, it would be better to merge them.

My concern was that the correct way to get these definitions from
userspace is very unclear, so there may be software out there
including <asm/auxvec.h> directly, which would now lack expected
definitions.

codesearch.debian.net shows no real hits for that, so maybe I'm too
paranoid.

Since <linux/auxvec.h> only contains #defines, it may be enough for arch
<asm/auxvec.h> headers to include <linux/auxvec.h>.

Thoughts?

Cheers
---Dave

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations
  2018-05-16 15:49   ` Dave Martin
@ 2018-05-16 23:09     ` H. Peter Anvin
  2018-05-16 23:21       ` Rich Felker
  0 siblings, 1 reply; 7+ messages in thread
From: H. Peter Anvin @ 2018-05-16 23:09 UTC (permalink / raw)
  To: Dave Martin, Rich Felker
  Cc: linux-kernel, x86, linux-arch, linux-api, Richard Henderson,
	Ivan Kokshaysky, Matt Turner, Russell King, Catalin Marinas,
	Will Deacon, Tony Luck, Fenghua Yu, Michal Simek, Ralf Baechle,
	James Hogan, Greentime Hu, Vincent Chen, Benjamin Herrenschmidt,
	Paul Mackerras, Michael Ellerman, Palmer Dabbelt, Albert Ou,
	Martin Schwidefsky, Heiko Carstens, Yoshinori Sato,
	David S. Miller, Thomas Gleixner, Ingo Molnar, Chris Zankel,
	Max Filippov

On 05/16/18 08:49, Dave Martin wrote:
> 
> Since <linux/auxvec.h> only contains #defines, it may be enough for arch
> <asm/auxvec.h> headers to include <linux/auxvec.h>.
> 

<asm/auxvec.h> doesn't seem to have any reason to exist at all. If
anyone includes it now, they are Doing It Wrong[TM] since
<linux/auxvec.h> includes <asm/auxvec.h>.

	-hpa


^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations
  2018-05-16 23:09     ` H. Peter Anvin
@ 2018-05-16 23:21       ` Rich Felker
  0 siblings, 0 replies; 7+ messages in thread
From: Rich Felker @ 2018-05-16 23:21 UTC (permalink / raw)
  To: H. Peter Anvin
  Cc: Dave Martin, linux-kernel, x86, linux-arch, linux-api,
	Richard Henderson, Ivan Kokshaysky, Matt Turner, Russell King,
	Catalin Marinas, Will Deacon, Tony Luck, Fenghua Yu,
	Michal Simek, Ralf Baechle, James Hogan, Greentime Hu,
	Vincent Chen, Benjamin Herrenschmidt, Paul Mackerras,
	Michael Ellerman, Palmer Dabbelt, Albert Ou, Martin Schwidefsky,
	Heiko Carstens, Yoshinori Sato, David S. Miller, Thomas Gleixner,
	Ingo Molnar, Chris Zankel, Max Filippov

On Wed, May 16, 2018 at 04:09:29PM -0700, H. Peter Anvin wrote:
> On 05/16/18 08:49, Dave Martin wrote:
> > 
> > Since <linux/auxvec.h> only contains #defines, it may be enough for arch
> > <asm/auxvec.h> headers to include <linux/auxvec.h>.
> > 
> 
> <asm/auxvec.h> doesn't seem to have any reason to exist at all. If
> anyone includes it now, they are Doing It Wrong[TM] since
> <linux/auxvec.h> includes <asm/auxvec.h>.

Sounds good. BTW there probably does need to be a check for
kernel-internal use of #ifdef AT_* etc. I saw some instances in
arch/um and a few other weird places. They might not matter but there
might be code that's indirectly enabled only for certain archs via the
AT_* macros.

Rich

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations
  2018-05-16 14:20 [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations Dave Martin
  2018-05-16 15:29 ` Rich Felker
@ 2018-05-17  6:40 ` Michael Ellerman
  2018-05-17 16:00 ` Yann Droneaud
  2 siblings, 0 replies; 7+ messages in thread
From: Michael Ellerman @ 2018-05-17  6:40 UTC (permalink / raw)
  To: Dave Martin, linux-kernel
  Cc: x86, linux-arch, linux-api, Richard Henderson, Ivan Kokshaysky,
	Matt Turner, Russell King, Catalin Marinas, Will Deacon,
	Tony Luck, Fenghua Yu, Michal Simek, Ralf Baechle, James Hogan,
	Greentime Hu, Vincent Chen, Benjamin Herrenschmidt,
	Paul Mackerras, Palmer Dabbelt, Albert Ou, Martin Schwidefsky,
	Heiko Carstens, Yoshinori Sato, Rich Felker, David S. Miller,
	Thomas Gleixner, Ingo Molnar, H. Peter Anvin, Chris Zankel,
	Max Filippov

Dave Martin <Dave.Martin@arm.com> writes:

> There are constraints on defining AT_* auxvec tags that are not
> obvious to the casual maintainer of either the global
> <uapi/linux/auxvec.h> or the arch-specific headers.  This is likely
> to lead to mistakes.  (I certainly fell foul of it...)

Thanks for cleaning this up.

It looks like us (powerpc) / me is the main offender here.

My excuse is it was glibc folk who asked us to add all those new AT_
entries in the first place. </buckpassing>

> For the benefit of future maintainers, this patch collects the
> relevant information in one place, documenting how the namespace
> needs to be managed, and noting all the values currently in use.
>
> Maintaining a global list may result in some merge conflicts, but
> AT_* values are not added frequently.  I'm open to suggestions on
> the best approach.

Yeah I agree with Rich that having a global list would be best. That is
the most reliable to make people think twice about adding new entries.

> I also assume that values 38 and 39 may have been used for
> historical purposes, such as an architecture that is no longer
> supported.  If they have definitely never been used for anything,
> they could be removed from the "reserved" list.

I don't know why we added the new entries starting at 40, maybe Ben
remembers. Quite likely it was just an accident.

I don't see any sign of 38 or 39 in glibc history.

cheers

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations
  2018-05-16 14:20 [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations Dave Martin
  2018-05-16 15:29 ` Rich Felker
  2018-05-17  6:40 ` Michael Ellerman
@ 2018-05-17 16:00 ` Yann Droneaud
  2 siblings, 0 replies; 7+ messages in thread
From: Yann Droneaud @ 2018-05-17 16:00 UTC (permalink / raw)
  To: Dave Martin, linux-kernel
  Cc: x86, linux-arch, linux-api, Richard Henderson, Ivan Kokshaysky,
	Matt Turner, Russell King, Catalin Marinas, Will Deacon,
	Tony Luck, Fenghua Yu, Michal Simek, Ralf Baechle, James Hogan,
	Greentime Hu, Vincent Chen, Benjamin Herrenschmidt,
	Paul Mackerras, Michael Ellerman, Palmer Dabbelt, Albert Ou,
	Martin Schwidefsky, Heiko Carstens, Yoshinori Sato, Rich Felker,
	David S. Miller, Thomas Gleixner, Ingo Molnar, H. Peter Anvin,
	Chris Zankel, Max Filippov, Michael Kerrisk

Hi,

Le mercredi 16 mai 2018 à 15:20 +0100, Dave Martin a écrit :
> There are constraints on defining AT_* auxvec tags that are not
> obvious to the casual maintainer of either the global
> <uapi/linux/auxvec.h> or the arch-specific headers.  This is likely
> to lead to mistakes.  (I certainly fell foul of it...)
> 
> For the benefit of future maintainers, this patch collects the
> relevant information in one place, documenting how the namespace
> needs to be managed, and noting all the values currently in use.
> 
> Maintaining a global list may result in some merge conflicts, but
> AT_* values are not added frequently.  I'm open to suggestions on
> the best approach.
> 
> I also assume that values 38 and 39 may have been used for
> historical purposes, such as an architecture that is no longer
> supported.  If they have definitely never been used for anything,
> they could be removed from the "reserved" list.
> 

Some of those AT_* values are described in getauxval(3) man-page:

http://man7.org/linux/man-pages/man3/getauxval.3.html

https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/man3/g
etauxval.3?id=4eae8eb731386d81797d5c30365426722410874e

And glibc provides <elf.h> with definitions for almost all AT_*,
regardless of the current target architecture:

https://sourceware.org/git/?p=glibc.git;a=blob;f=elf/elf.h;h=954f3266f7
11ab83996670ea504a17dcf668e061;hb=23158b08a0908f381459f273a984c6fd32836
3cb#l1135

Also, despite not being listed as a reserved namespace by POSIX, one
should try to avoid name collision with other AT_ constants,
those used with *at() functions (openat(), etc.):

- AT_EACCESS 
- AT_EMPTY_PATH
- AT_FDCWD
- AT_NO_AUTOMOUNT
- AT_REMOVEDIR
- AT_STATX_DONT_SYNC
- AT_STATX_FORCE_SYNC
- AT_STATX_SYNC_AS_STAT
- AT_SYMLINK_FOLLOW
- AT_SYMLINK_NOFOLLOW

http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/fcntl.h.html

http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.htm
l#tag_15_02_02

https://sourceware.org/git/?p=glibc.git;a=blob;f=io/fcntl.h;h=3d239e8f0
9f7ce0a3106621be327e1ea4cd1a3e7;hb=23158b08a0908f381459f273a984c6fd3283
63cb#l142

And there's also AT_ANYNET and AT_ANYNODE from ddp (aka. AppleTalk)

http://man7.org/linux/man-pages/man7/ddp.7.html

Regards.

-- 
Yann Droneaud
OPTEYA


^ permalink raw reply	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2018-05-17 16:43 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-05-16 14:20 [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations Dave Martin
2018-05-16 15:29 ` Rich Felker
2018-05-16 15:49   ` Dave Martin
2018-05-16 23:09     ` H. Peter Anvin
2018-05-16 23:21       ` Rich Felker
2018-05-17  6:40 ` Michael Ellerman
2018-05-17 16:00 ` Yann Droneaud

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