[PATCH v3] Add possibility for the user to print system calls available in the platform.

[Dmitry V. Levin]

On Wed, Aug 03, 2016 at 06:19:30PM +0200, Amin Khorsandi wrote:
> ---
>  defs.h    |  1 +
>  strace.1  |  7 +++++++
>  syscall.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
>  3 files changed, 62 insertions(+), 3 deletions(-)
> 
> diff --git a/defs.h b/defs.h
> index 4b7e8ed..a8e71c8 100644
> --- a/defs.h
> +++ b/defs.h
> @@ -363,6 +363,7 @@ struct tcb {
>  #define QUAL_SIGNAL	0x010	/* report events with this signal */
>  #define QUAL_READ	0x020	/* dump data read on this file descriptor */
>  #define QUAL_WRITE	0x040	/* dump data written to this file descriptor */
> +#define QUAL_LIST	0x060   /* this system call should be listed */

You are asking for trouble: QUAL_LIST == QUAL_READ|QUAL_WRITE

>  typedef uint8_t qualbits_t;
>  
>  #define DEFAULT_QUAL_FLAGS (QUAL_TRACE | QUAL_ABBREV | QUAL_VERBOSE)
> diff --git a/strace.1 b/strace.1
> index 6cc17c5..2c06bbd 100644
> --- a/strace.1
> +++ b/strace.1
> @@ -481,6 +481,13 @@ Note that this is independent from the normal tracing of the
>  system call which is controlled by the option
>  .BR -e "\ " trace = write .
>  .TP
> +\fB\-e\ list_syscalls\fR=\,\fIset\fR
> +List system calls available on the current platform in the specified set.
> +For example,
> +.BR -e "\ " list_syscalls = file
> +lists all system calls related to the file operations available in the current
> +platform.
> +.TP

The longer I look at this extension, the more I inclined to add a new
option.  For example, how would you like "-l trace" that lists all syscalls
selected using traditional "-e trace=set" syntax?

>  .BI "\-I " interruptible
>  When strace can be interrupted by signals (such as pressing ^C).
>  1: no signals are blocked; 2: fatal signals are blocked while decoding syscall
> diff --git a/syscall.c b/syscall.c
> index 6af0dec..c083e7c 100644
> --- a/syscall.c
> +++ b/syscall.c
> @@ -360,6 +360,7 @@ update_personality(struct tcb *tcp, unsigned int personality)
>  #endif
>  
>  static int qual_syscall(), qual_signal(), qual_desc();
> +static void print_syscalls(const char *list);
>  
>  static const struct qual_options {
>  	unsigned int bitflag;
> @@ -384,6 +385,8 @@ static const struct qual_options {
>  	{ QUAL_WRITE,	"write",	qual_desc,	"descriptor"	},
>  	{ QUAL_WRITE,	"writes",	qual_desc,	"descriptor"	},
>  	{ QUAL_WRITE,	"w",		qual_desc,	"descriptor"	},
> +	{ QUAL_LIST,	"list_syscalls",	qual_syscall,	"system call"	},
> +	{ QUAL_LIST,	"l",	qual_syscall,	"system call"	},
>  	{ 0,		NULL,		NULL,		NULL		},
>  };
>  
> @@ -484,6 +487,42 @@ qual_desc(const char *s, const unsigned int bitflag, const int not)
>  }
>  
>  static int
> +value_already_in_list(const char *value, const char ** list, int size) 
> +{
> +	int i;
> +	for (i=0; i < size; i++) {
> +		if (list[i] == value)
> +			return 1;

Here you rely on the linker that would hopefully place all identical
strings at same addresses.  This is fragile.

> +	}
> +	return 0;
> +}
> +
> +static void
> +print_syscalls(const char *set)
> +{
> +	unsigned int p, i;
> +	const char *syscalls_list[MAX_NSYSCALLS] = {NULL};
> +
> +	for (p = 0; p < SUPPORTED_PERSONALITIES; p++) {
> +		for (i = 0; i<nsyscall_vec[p]; i++)
> +			if(((qual_vec[p][i] & QUAL_LIST) == QUAL_LIST) &&
> +				(sysent_vec[p][i].sys_name != NULL))
> +				if (!value_already_in_list(sysent_vec[p][i].sys_name,
> +					syscalls_list, MAX_NSYSCALLS))
> +					syscalls_list[p*i+i] = sysent_vec[p][i].sys_name;

Wouldn't this cause a stack overflow if
nsyscall_vec[2] > 1 + MAX_NSYSCALLS/3 ?

Try e.g. "strace -e list_syscalls=all" on x86_64.

> +	}
> +
> +	fprintf(stdout, "System calls in %s (current platform):\n", set);
> +	fprintf(stdout, "------------------------------------------------\n");
> +
> +	for (i=0; i < MAX_NSYSCALLS; i++){
> +		if (syscalls_list[i] != NULL)
> +			fprintf(stdout,  "%s\n", syscalls_list[i]);
> +	}

The output should go to shared_log instead of stdout.


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