* [PATCH] arm64: use sregs for syscall probe registers
@ 2019-04-12 17:30 Frank van der Linden
2019-04-15 21:32 ` William Cohen
2019-04-16 15:33 ` Frank Ch. Eigler
0 siblings, 2 replies; 4+ messages in thread
From: Frank van der Linden @ 2019-04-12 17:30 UTC (permalink / raw)
To: systemtap
Since syscall wrappers are now active on arm64 (4.19+), arguments need to
be retrieved the right way, by checking if there is a saved set of system
call registers, and using them if there are.
---
tapset/arm64/registers.stp | 50 ++++++++++++++++++++++++++++------------------
1 file changed, 31 insertions(+), 19 deletions(-)
diff --git a/tapset/arm64/registers.stp b/tapset/arm64/registers.stp
index b2e56495d..b001b8efe 100644
--- a/tapset/arm64/registers.stp
+++ b/tapset/arm64/registers.stp
@@ -107,6 +107,36 @@ function u_register:long (name:string) {
return _stp_register(name, 0)
}
+function _stp_arg_register:long (argnum:long) %{ /* pure */
+ long val;
+ struct pt_regs *regs;
+
+ if (STAP_ARG_argnum < 1 || STAP_ARG_argnum > 8) {
+ snprintf(CONTEXT->error_buffer, sizeof(CONTEXT->error_buffer),
+ "Cannot access arg(%lld)",
+ (long long)STAP_ARG_argnum);
+ CONTEXT->last_error = CONTEXT->error_buffer;
+ return;
+ }
+
+ /* syscall-in-pt_regs mode, 4.19+ */
+ if (CONTEXT->sregs) {
+ regs = CONTEXT->sregs;
+ } else {
+ regs = (CONTEXT->user_mode_p ? CONTEXT->uregs : CONTEXT->kregs);
+ }
+
+ if (!regs) {
+ CONTEXT->last_error = "No registers available in this context";
+ return;
+ }
+
+ memcpy(&val, ((char *)regs) + ((STAP_ARG_argnum - 1) * sizeof (long)),
+ sizeof (long));
+
+ STAP_RETVALUE = val;
+%}
+
/*
* Return the value of function arg #argnum (1=first arg).
* If truncate=1, mask off the top 32 bits.
@@ -115,25 +145,7 @@ function u_register:long (name:string) {
* TODO: 32-bit arm code has different calling conventions than arm64
*/
function _stp_arg:long (argnum:long, sign_extend:long, truncate:long) {
- val = 0
- assert(!(argnum < 1 || argnum > 8), sprintf("Cannot access arg(%d)", argnum))
-
- if (argnum == 1)
- val = u_register("x0")
- else if (argnum == 2)
- val = u_register("x1")
- else if (argnum == 3)
- val = u_register("x2")
- else if (argnum == 4)
- val = u_register("x3")
- else if (argnum == 5)
- val = u_register("x4")
- else if (argnum == 6)
- val = u_register("x5")
- else if (argnum == 7)
- val = u_register("x6")
- else if (argnum == 8)
- val = u_register("x7")
+ val = _stp_arg_register(argnum)
if (truncate) {
if (sign_extend)
--
2.16.5
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] arm64: use sregs for syscall probe registers
2019-04-12 17:30 [PATCH] arm64: use sregs for syscall probe registers Frank van der Linden
@ 2019-04-15 21:32 ` William Cohen
2019-04-15 21:40 ` van der Linden, Frank
2019-04-16 15:33 ` Frank Ch. Eigler
1 sibling, 1 reply; 4+ messages in thread
From: William Cohen @ 2019-04-15 21:32 UTC (permalink / raw)
To: Frank van der Linden, systemtap
On 4/12/19 1:30 PM, Frank van der Linden wrote:
> Since syscall wrappers are now active on arm64 (4.19+), arguments need to
> be retrieved the right way, by checking if there is a saved set of system
> call registers, and using them if there are.
> ---
> tapset/arm64/registers.stp | 50 ++++++++++++++++++++++++++++------------------
> 1 file changed, 31 insertions(+), 19 deletions(-)
>
> diff --git a/tapset/arm64/registers.stp b/tapset/arm64/registers.stp
> index b2e56495d..b001b8efe 100644
> --- a/tapset/arm64/registers.stp
> +++ b/tapset/arm64/registers.stp
> @@ -107,6 +107,36 @@ function u_register:long (name:string) {
> return _stp_register(name, 0)
> }
>
> +function _stp_arg_register:long (argnum:long) %{ /* pure */
> + long val;
> + struct pt_regs *regs;
> +
> + if (STAP_ARG_argnum < 1 || STAP_ARG_argnum > 8) {
> + snprintf(CONTEXT->error_buffer, sizeof(CONTEXT->error_buffer),
> + "Cannot access arg(%lld)",
> + (long long)STAP_ARG_argnum);
> + CONTEXT->last_error = CONTEXT->error_buffer;
> + return;
> + }
> +
> + /* syscall-in-pt_regs mode, 4.19+ */
> + if (CONTEXT->sregs) {
> + regs = CONTEXT->sregs;
> + } else {
> + regs = (CONTEXT->user_mode_p ? CONTEXT->uregs : CONTEXT->kregs);
> + }
> +
> + if (!regs) {
> + CONTEXT->last_error = "No registers available in this context";
> + return;
> + }
> +
> + memcpy(&val, ((char *)regs) + ((STAP_ARG_argnum - 1) * sizeof (long)),
> + sizeof (long));
> +
> + STAP_RETVALUE = val;
Could the memcpy be eliminated and STAP_RETVALUE statements be simplified to something like:
STAP_RETVALUE = regs->regs[STAP_ARG_argnum-1];
-Will
> +%}
> +
> /*
> * Return the value of function arg #argnum (1=first arg).
> * If truncate=1, mask off the top 32 bits.
> @@ -115,25 +145,7 @@ function u_register:long (name:string) {
> * TODO: 32-bit arm code has different calling conventions than arm64
> */
> function _stp_arg:long (argnum:long, sign_extend:long, truncate:long) {
> - val = 0
> - assert(!(argnum < 1 || argnum > 8), sprintf("Cannot access arg(%d)", argnum))
> -
> - if (argnum == 1)
> - val = u_register("x0")
> - else if (argnum == 2)
> - val = u_register("x1")
> - else if (argnum == 3)
> - val = u_register("x2")
> - else if (argnum == 4)
> - val = u_register("x3")
> - else if (argnum == 5)
> - val = u_register("x4")
> - else if (argnum == 6)
> - val = u_register("x5")
> - else if (argnum == 7)
> - val = u_register("x6")
> - else if (argnum == 8)
> - val = u_register("x7")
> + val = _stp_arg_register(argnum)
>
> if (truncate) {
> if (sign_extend)
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] arm64: use sregs for syscall probe registers
2019-04-15 21:32 ` William Cohen
@ 2019-04-15 21:40 ` van der Linden, Frank
0 siblings, 0 replies; 4+ messages in thread
From: van der Linden, Frank @ 2019-04-15 21:40 UTC (permalink / raw)
To: William Cohen, systemtap
On 4/15/19, 2:32 PM, "William Cohen" <wcohen@redhat.com> wrote:
On 4/12/19 1:30 PM, Frank van der Linden wrote:
> Since syscall wrappers are now active on arm64 (4.19+), arguments need to
> be retrieved the right way, by checking if there is a saved set of system
> call registers, and using them if there are.
> ---
> tapset/arm64/registers.stp | 50 ++++++++++++++++++++++++++++------------------
> 1 file changed, 31 insertions(+), 19 deletions(-)
>
> diff --git a/tapset/arm64/registers.stp b/tapset/arm64/registers.stp
> index b2e56495d..b001b8efe 100644
> --- a/tapset/arm64/registers.stp
> +++ b/tapset/arm64/registers.stp
> @@ -107,6 +107,36 @@ function u_register:long (name:string) {
> return _stp_register(name, 0)
> }
>
> +function _stp_arg_register:long (argnum:long) %{ /* pure */
> + long val;
> + struct pt_regs *regs;
> +
> + if (STAP_ARG_argnum < 1 || STAP_ARG_argnum > 8) {
> + snprintf(CONTEXT->error_buffer, sizeof(CONTEXT->error_buffer),
> + "Cannot access arg(%lld)",
> + (long long)STAP_ARG_argnum);
> + CONTEXT->last_error = CONTEXT->error_buffer;
> + return;
> + }
> +
> + /* syscall-in-pt_regs mode, 4.19+ */
> + if (CONTEXT->sregs) {
> + regs = CONTEXT->sregs;
> + } else {
> + regs = (CONTEXT->user_mode_p ? CONTEXT->uregs : CONTEXT->kregs);
> + }
> +
> + if (!regs) {
> + CONTEXT->last_error = "No registers available in this context";
> + return;
> + }
> +
> + memcpy(&val, ((char *)regs) + ((STAP_ARG_argnum - 1) * sizeof (long)),
> + sizeof (long));
> +
> + STAP_RETVALUE = val;
> Could the memcpy be eliminated and STAP_RETVALUE statements be simplified to something like:
>
> STAP_RETVALUE = regs->regs[STAP_ARG_argnum-1];
>
>-Will
Probably. I was following existing practice and used memcpy. See also _stp_get_register_by_offset() for various architectures: they all use memcpy. I am not sure why. Alignment paranoia?
Frank
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] arm64: use sregs for syscall probe registers
2019-04-12 17:30 [PATCH] arm64: use sregs for syscall probe registers Frank van der Linden
2019-04-15 21:32 ` William Cohen
@ 2019-04-16 15:33 ` Frank Ch. Eigler
1 sibling, 0 replies; 4+ messages in thread
From: Frank Ch. Eigler @ 2019-04-16 15:33 UTC (permalink / raw)
To: Frank van der Linden; +Cc: systemtap
Frank van der Linden <fllinden@amazon.com> writes:
> Since syscall wrappers are now active on arm64 (4.19+), arguments need to
> be retrieved the right way, by checking if there is a saved set of system
> call registers, and using them if there are. [...]
This looks good to me.
> + if (STAP_ARG_argnum < 1 || STAP_ARG_argnum > 8) {
> + snprintf(CONTEXT->error_buffer, sizeof(CONTEXT->error_buffer),
> + "Cannot access arg(%lld)",
> + (long long)STAP_ARG_argnum);
> + CONTEXT->last_error = CONTEXT->error_buffer;
> + return;
> + }
By the way, as listed in [man stap], there are some helper macros to
make this a little more compact:
if (...) {
STAP_ERROR("foo bar %lld", (long long)foo);
}
- FChE
^ permalink raw reply [flat|nested] 4+ messages in thread
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2019-04-12 17:30 [PATCH] arm64: use sregs for syscall probe registers Frank van der Linden
2019-04-15 21:32 ` William Cohen
2019-04-15 21:40 ` van der Linden, Frank
2019-04-16 15:33 ` Frank Ch. Eigler
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