[PATCH 0/3] rcutorture: minor nolibc fixes

[PATCH 0/3] rcutorture: minor nolibc fixes

[Willy Tarreau]

While working on adding some documentation to the nolibc header provided
with rcutorture, I noticed a few accidently deleted lines losing clobbered
registers and some leftover spaces that I fixed. In addition, I finally
added some documentation to the file, as requested by Ingo.

Willy Tarreau (3):
  rcutorture/nolibc: fix the clobbered registers in the MIPS syscall
    definition
  rcutorture/nolibc: fix some poor indentation and alignment
  rcutorture/nolibc: add a bit of documentation to explain how to use
    nolibc

 tools/testing/selftests/rcutorture/bin/nolibc.h | 116 +++++++++++++++++++-----
 1 file changed, 91 insertions(+), 25 deletions(-)

-- 
2.9.0

[PATCH 1/3] rcutorture/nolibc: fix the clobbered registers in the MIPS syscall definition

[Willy Tarreau]

A last-minute checkpatch cleanup caused most of list of clobbered
registers to be lost in the MIPS syscall definition. As it is right
now the code is not used on MIPS, but it's better to fix it before
it gets used.

Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
 tools/testing/selftests/rcutorture/bin/nolibc.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/rcutorture/bin/nolibc.h b/tools/testing/selftests/rcutorture/bin/nolibc.h
index f98f5b9..30bd27b 100644
--- a/tools/testing/selftests/rcutorture/bin/nolibc.h
+++ b/tools/testing/selftests/rcutorture/bin/nolibc.h
@@ -1006,7 +1006,7 @@ struct sys_stat_struct {
 		: "=r"(_num), "=r"(_arg4)                                     \
 		: "r"(_num)                                                   \
 		: "memory", "cc", "at", "v1", "hi", "lo",                     \
-									      \
+	          "t0", "t1", "t2", "t3", "t4", "t5", "t6", "t7", "t8", "t9"  \
 	);                                                                    \
 	_arg4 ? -_num : _num;                                                 \
 })
@@ -1025,7 +1025,7 @@ struct sys_stat_struct {
 		: "0"(_num),                                                  \
 		  "r"(_arg1)                                                  \
 		: "memory", "cc", "at", "v1", "hi", "lo",                     \
-									      \
+	          "t0", "t1", "t2", "t3", "t4", "t5", "t6", "t7", "t8", "t9"  \
 	);                                                                    \
 	_arg4 ? -_num : _num;                                                 \
 })
@@ -1045,7 +1045,7 @@ struct sys_stat_struct {
 		: "0"(_num),                                                  \
 		  "r"(_arg1), "r"(_arg2)                                      \
 		: "memory", "cc", "at", "v1", "hi", "lo",                     \
-									      \
+	          "t0", "t1", "t2", "t3", "t4", "t5", "t6", "t7", "t8", "t9"  \
 	);                                                                    \
 	_arg4 ? -_num : _num;                                                 \
 })
@@ -1066,7 +1066,7 @@ struct sys_stat_struct {
 		: "0"(_num),                                                  \
 		  "r"(_arg1), "r"(_arg2), "r"(_arg3)                          \
 		: "memory", "cc", "at", "v1", "hi", "lo",                     \
-									      \
+	          "t0", "t1", "t2", "t3", "t4", "t5", "t6", "t7", "t8", "t9"  \
 	);                                                                    \
 	_arg4 ? -_num : _num;                                                 \
 })
@@ -1087,7 +1087,7 @@ struct sys_stat_struct {
 		: "0"(_num),                                                  \
 		  "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4)              \
 		: "memory", "cc", "at", "v1", "hi", "lo",                     \
-									      \
+	          "t0", "t1", "t2", "t3", "t4", "t5", "t6", "t7", "t8", "t9"  \
 	);                                                                    \
 	_arg4 ? -_num : _num;                                                 \
 })
@@ -1110,7 +1110,7 @@ struct sys_stat_struct {
 		: "0"(_num),                                                  \
 		  "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5)  \
 		: "memory", "cc", "at", "v1", "hi", "lo",                     \
-									      \
+	          "t0", "t1", "t2", "t3", "t4", "t5", "t6", "t7", "t8", "t9"  \
 	);                                                                    \
 	_arg4 ? -_num : _num;                                                 \
 })
-- 
2.9.0

[PATCH 2/3] rcutorture/nolibc: fix some poor indentation and alignment

[Willy Tarreau]

A few macros had their rightmost backslash misaligned, and the pollfd
struct definition resisted the previous code reindent. Nothing else
changed.

Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
 tools/testing/selftests/rcutorture/bin/nolibc.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/rcutorture/bin/nolibc.h b/tools/testing/selftests/rcutorture/bin/nolibc.h
index 30bd27b..985364c 100644
--- a/tools/testing/selftests/rcutorture/bin/nolibc.h
+++ b/tools/testing/selftests/rcutorture/bin/nolibc.h
@@ -81,9 +81,9 @@ typedef   signed long        time_t;
 
 /* for poll() */
 struct pollfd {
-    int fd;
-    short int events;
-    short int revents;
+	int fd;
+	short int events;
+	short int revents;
 };
 
 /* for select() */
@@ -239,7 +239,7 @@ struct stat {
 		"syscall\n"                                                   \
 		: "=a" (_ret)                                                 \
 		: "0"(_num)                                                   \
-		: "rcx", "r8", "r9", "r10", "r11", "memory", "cc"                                \
+		: "rcx", "r8", "r9", "r10", "r11", "memory", "cc"             \
 	);                                                                    \
 	_ret;                                                                 \
 })
@@ -255,7 +255,7 @@ struct stat {
 		: "=a" (_ret)                                                 \
 		: "r"(_arg1),                                                 \
 		  "0"(_num)                                                   \
-		: "rcx", "r8", "r9", "r10", "r11", "memory", "cc"                                \
+		: "rcx", "r8", "r9", "r10", "r11", "memory", "cc"             \
 	);                                                                    \
 	_ret;                                                                 \
 })
@@ -272,7 +272,7 @@ struct stat {
 		: "=a" (_ret)                                                 \
 		: "r"(_arg1), "r"(_arg2),                                     \
 		  "0"(_num)                                                   \
-		: "rcx", "r8", "r9", "r10", "r11", "memory", "cc"                                \
+		: "rcx", "r8", "r9", "r10", "r11", "memory", "cc"             \
 	);                                                                    \
 	_ret;                                                                 \
 })
@@ -290,7 +290,7 @@ struct stat {
 		: "=a" (_ret)                                                 \
 		: "r"(_arg1), "r"(_arg2), "r"(_arg3),                         \
 		  "0"(_num)                                                   \
-		: "rcx", "r8", "r9", "r10", "r11", "memory", "cc"                                \
+		: "rcx", "r8", "r9", "r10", "r11", "memory", "cc"             \
 	);                                                                    \
 	_ret;                                                                 \
 })
-- 
2.9.0

[PATCH 3/3] rcutorture/nolibc: add a bit of documentation to explain how to use nolibc

[Willy Tarreau]

Ingo rightfully asked for a bit more documentation in the nolibc header,
so this patch adds some explanation about its purpose, how it's made, and
how to use it.

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
 tools/testing/selftests/rcutorture/bin/nolibc.h | 90 +++++++++++++++++++++----
 1 file changed, 78 insertions(+), 12 deletions(-)

diff --git a/tools/testing/selftests/rcutorture/bin/nolibc.h b/tools/testing/selftests/rcutorture/bin/nolibc.h
index 985364c..20d15a6 100644
--- a/tools/testing/selftests/rcutorture/bin/nolibc.h
+++ b/tools/testing/selftests/rcutorture/bin/nolibc.h
@@ -3,6 +3,84 @@
  * Copyright (C) 2017-2018 Willy Tarreau <w@1wt.eu>
  */
 
+/*
+ * This file is designed to be used as a libc alternative for minimal programs
+ * with very limited requirements. It consists of a small number of syscall and
+ * types definitions, and the minimal startup code needed to call main().
+ * All syscalls are declared as static functions so that they can be optimized
+ * away by the compiler when not used.
+ *
+ * Syscalls are split between 3 levels :
+ *   - the lower level is the arch-specific syscall() definition, consisting in
+ *     assembly code in compound expressions. These ones are called
+ *     my_syscall0() to my_syscall6() depending on the number of arguments. The
+ *     MIPS implementation is limited to 5 arguments. All input arguments are
+ *     cast to a long stored in a register. These expressions always return the
+ *     syscall's return value as a signed long value which is often either a
+ *     pointer or the negated errno value.
+ *
+ *   - the second level is mostly architecture-independent. It is made of
+ *     static functions called sys_<name>() which rely on my_syscallN()
+ *     depending on the syscall definition. These functions are responsible
+ *     for exposing the appropriate types for the syscall arguments (int,
+ *     pointers, etc) and for setting the appropriate return type (often int).
+ *     A few of them are architecture-specific because the syscalls are not all
+ *     mapped exactly the same between architecture. For example, some archs do
+ *     not implement select() and need pselect6() instead, so the sys_select()
+ *     function will have to abstract this.
+ *
+ *   - the third level is the libc call definition. It exposes the lower raw
+ *     sys_<name>() calls in a way that looks like what a libc usually does,
+ *     takes care of specific input values, and of setting errno upon error.
+ *     There can be minor variations compared to standard libc calls. For
+ *     example the open() call always takes 3 args here.
+ *
+ * The errno variable is declared static and unused. This way it can be
+ * optimized away if not used. However this means that a program made of
+ * multiple C files may observe different errno values (one per C file). For
+ * the type of programs this project targets it usually is not a problem. The
+ * resulting program may even be reduced by defining the NOLIBC_IGNORE_ERRNO
+ * macro, in which case the errno value will never be assigned.
+ *
+ * Some stdint-like integer types are defined. These ones are valid on all
+ * currently supported architecture, because signs are enforced, ints are
+ * assumed to be 32 bits, longs the size of a pointer and long long 64 bits.
+ * If more architectures have to be supported, this may need to be adapted.
+ *
+ * Some macro definitions like the O_* values passed to open(), and some
+ * structures like the sys_stat struct depend on the architecture.
+ *
+ * The definitions start with the architecture-specific parts, which are picked
+ * based on what the compiler knows about the target architecture, and are
+ * completed with the generic code. Since it is the compiler which sets the
+ * target architecture, cross-compiling normally works out of the box without
+ * having to specify anything.
+ *
+ * Finally some very common libc-level functions are provided. It is the case
+ * for a few functions usually found in string.h, ctype.h, or stdlib.h. Nothing
+ * is currently provided regarding stdio emulation.
+ *
+ * The macro NOLIBC is always defined, so that it is possible for a program to
+ * check this macro to know if it is being built against and decide to disable
+ * some features or simply not to include some standard libc files.
+ *
+ * Ideally this file should be split in multiple files for easier long term
+ * maintenance, but provided as a single file as it is now, it's quite
+ * convenient to use. Maybe some variations involving a set of includes at the
+ * top could work.
+ *
+ * A simple static executable may be built this way :
+ *      $ gcc -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \
+ *            -static -include nolibc.h -lgcc -o hello hello.c
+ *
+ * A very useful calling convention table may be found here :
+ *      http://man7.org/linux/man-pages/man2/syscall.2.html
+ *
+ * This doc is quite convenient though not necessarily up to date :
+ *      https://w3challs.com/syscalls/
+ *
+ */
+
 /* some archs (at least aarch64) don't expose the regular syscalls anymore by
  * default, either because they have an "_at" replacement, or because there are
  * more modern alternatives. For now we'd rather still use them.
@@ -19,18 +97,6 @@
 
 #define NOLIBC
 
-/* Build a static executable this way :
- *      $ gcc -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \
- *            -static -include nolibc.h -lgcc -o hello hello.c
- *
- * Useful calling convention table found here :
- *      http://man7.org/linux/man-pages/man2/syscall.2.html
- *
- * This doc is even better :
- *      https://w3challs.com/syscalls/
- */
-
-
 /* this way it will be removed if unused */
 static int errno;
 
-- 
2.9.0

Re: [PATCH 3/3] rcutorture/nolibc: add a bit of documentation to explain how to use nolibc

[Randy Dunlap]

On 12/29/18 7:58 AM, Willy Tarreau wrote:
> Ingo rightfully asked for a bit more documentation in the nolibc header,
> so this patch adds some explanation about its purpose, how it's made, and
> how to use it.
> 
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Willy Tarreau <w@1wt.eu>

Hi Willy,

This is a good summary IMO.  Thanks.
And it's in good shape -- doesn't *require* any fixes.
But if you do make any changes to it, here are a few suggestions.  :)


> ---
>  tools/testing/selftests/rcutorture/bin/nolibc.h | 90 +++++++++++++++++++++----
>  1 file changed, 78 insertions(+), 12 deletions(-)
> 
> diff --git a/tools/testing/selftests/rcutorture/bin/nolibc.h b/tools/testing/selftests/rcutorture/bin/nolibc.h
> index 985364c..20d15a6 100644
> --- a/tools/testing/selftests/rcutorture/bin/nolibc.h
> +++ b/tools/testing/selftests/rcutorture/bin/nolibc.h
> @@ -3,6 +3,84 @@
>   * Copyright (C) 2017-2018 Willy Tarreau <w@1wt.eu>
>   */
>  
> +/*
> + * This file is designed to be used as a libc alternative for minimal programs
> + * with very limited requirements. It consists of a small number of syscall and
> + * types definitions, and the minimal startup code needed to call main().

      type

> + * All syscalls are declared as static functions so that they can be optimized
> + * away by the compiler when not used.
> + *
> + * Syscalls are split between 3 levels :

Instead of "between", use either "among" or "into".  and then "levels:".

> + *   - the lower level is the arch-specific syscall() definition, consisting in
> + *     assembly code in compound expressions. These ones are called

Apparently "these ones" is acceptable in UK English, not so in US English.
I don't like it, but we do accept UK English here.  :)

> + *     my_syscall0() to my_syscall6() depending on the number of arguments. The
> + *     MIPS implementation is limited to 5 arguments. All input arguments are
> + *     cast to a long stored in a register. These expressions always return the
> + *     syscall's return value as a signed long value which is often either a
> + *     pointer or the negated errno value.
> + *
> + *   - the second level is mostly architecture-independent. It is made of
> + *     static functions called sys_<name>() which rely on my_syscallN()
> + *     depending on the syscall definition. These functions are responsible
> + *     for exposing the appropriate types for the syscall arguments (int,
> + *     pointers, etc) and for setting the appropriate return type (often int).
> + *     A few of them are architecture-specific because the syscalls are not all
> + *     mapped exactly the same between architecture. For example, some archs do
> + *     not implement select() and need pselect6() instead, so the sys_select()
> + *     function will have to abstract this.
> + *
> + *   - the third level is the libc call definition. It exposes the lower raw
> + *     sys_<name>() calls in a way that looks like what a libc usually does,
> + *     takes care of specific input values, and of setting errno upon error.
> + *     There can be minor variations compared to standard libc calls. For
> + *     example the open() call always takes 3 args here.
> + *
> + * The errno variable is declared static and unused. This way it can be
> + * optimized away if not used. However this means that a program made of
> + * multiple C files may observe different errno values (one per C file). For
> + * the type of programs this project targets it usually is not a problem. The
> + * resulting program may even be reduced by defining the NOLIBC_IGNORE_ERRNO
> + * macro, in which case the errno value will never be assigned.
> + *
> + * Some stdint-like integer types are defined. These ones are valid on all

                                                  These are valid on all
(or not :)

> + * currently supported architecture, because signs are enforced, ints are
> + * assumed to be 32 bits, longs the size of a pointer and long long 64 bits.
> + * If more architectures have to be supported, this may need to be adapted.
> + *
> + * Some macro definitions like the O_* values passed to open(), and some
> + * structures like the sys_stat struct depend on the architecture.
> + *
> + * The definitions start with the architecture-specific parts, which are picked
> + * based on what the compiler knows about the target architecture, and are
> + * completed with the generic code. Since it is the compiler which sets the
> + * target architecture, cross-compiling normally works out of the box without
> + * having to specify anything.
> + *
> + * Finally some very common libc-level functions are provided. It is the case
> + * for a few functions usually found in string.h, ctype.h, or stdlib.h. Nothing
> + * is currently provided regarding stdio emulation.
> + *
> + * The macro NOLIBC is always defined, so that it is possible for a program to
> + * check this macro to know if it is being built against and decide to disable
> + * some features or simply not to include some standard libc files.
> + *
> + * Ideally this file should be split in multiple files for easier long term
> + * maintenance, but provided as a single file as it is now, it's quite
> + * convenient to use. Maybe some variations involving a set of includes at the
> + * top could work.
> + *
> + * A simple static executable may be built this way :
> + *      $ gcc -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \
> + *            -static -include nolibc.h -lgcc -o hello hello.c
> + *
> + * A very useful calling convention table may be found here :
> + *      http://man7.org/linux/man-pages/man2/syscall.2.html
> + *
> + * This doc is quite convenient though not necessarily up to date :
> + *      https://w3challs.com/syscalls/
> + *
> + */
> +
>  /* some archs (at least aarch64) don't expose the regular syscalls anymore by
>   * default, either because they have an "_at" replacement, or because there are
>   * more modern alternatives. For now we'd rather still use them.
> @@ -19,18 +97,6 @@
>  
>  #define NOLIBC
>  
> -/* Build a static executable this way :
> - *      $ gcc -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \
> - *            -static -include nolibc.h -lgcc -o hello hello.c
> - *
> - * Useful calling convention table found here :
> - *      http://man7.org/linux/man-pages/man2/syscall.2.html
> - *
> - * This doc is even better :
> - *      https://w3challs.com/syscalls/
> - */
> -
> -
>  /* this way it will be removed if unused */
>  static int errno;
>  
> 

ciao.  thanks.
-- 
~Randy

Re: [PATCH 3/3] rcutorture/nolibc: add a bit of documentation to explain how to use nolibc

[Willy Tarreau]

Hi Randy,

On Sat, Dec 29, 2018 at 08:50:09AM -0800, Randy Dunlap wrote:
> This is a good summary IMO.  Thanks.
> And it's in good shape -- doesn't *require* any fixes.
> But if you do make any changes to it, here are a few suggestions.  :)

Thanks very much.

> > + * This file is designed to be used as a libc alternative for minimal programs
> > + * with very limited requirements. It consists of a small number of syscall and
> > + * types definitions, and the minimal startup code needed to call main().
> 
>       type

Funny, I hesitated on this one and "fixed" it :-)

> > + * All syscalls are declared as static functions so that they can be optimized
> > + * away by the compiler when not used.
> > + *
> > + * Syscalls are split between 3 levels :
> 
> Instead of "between", use either "among" or "into".  and then "levels:".

Will do, thanks.

> > + *   - the lower level is the arch-specific syscall() definition, consisting in
> > + *     assembly code in compound expressions. These ones are called
> 
> Apparently "these ones" is acceptable in UK English, not so in US English.

Oh I didn't know, I've used it quite a bit in the last decades, thinking
it was a valid plural for "this one". It seems like I should use "These"
instead, feel free to suggest otherwise.

> I don't like it, but we do accept UK English here.  :)

I prefer to be corrected and to avoid using bad English, whether it's
US or UK, as much as I hate to make mistakes in French.

> > + * Some stdint-like integer types are defined. These ones are valid on all
> 
>                                                   These are valid on all

OK, makes sense according to the point above.

> ciao.  thanks.

I'm applying the changes right now to my local tree and will respin a
version. Thank you!

Willy