* [PATCH v2 bpf-next] libbpf: usdt arm arg parsing support
@ 2023-03-03 8:37 Puranjay Mohan
2023-03-04 4:22 ` Andrii Nakryiko
0 siblings, 1 reply; 4+ messages in thread
From: Puranjay Mohan @ 2023-03-03 8:37 UTC (permalink / raw)
To: andrii, ast, daniel, martin.lau, song, yhs, bpf, memxor; +Cc: Puranjay Mohan
Parsing of USDT arguments is architecture-specific; on arm it is
relatively easy since registers used are r[0-10], fp, ip, sp, lr,
pc. Format is slightly different compared to aarch64; forms are
- "size @ [ reg, #offset ]" for dereferences, for example
"-8 @ [ sp, #76 ]" ; " -4 @ [ sp ]"
- "size @ reg" for register values; for example
"-4@r0"
- "size @ #value" for raw values; for example
"-8@#1"
Add support for parsing USDT arguments for ARM architecture.
Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
---
Changes in V1[1] to V2
- Resending as V1 shows up as Superseded in patchwork.
[1] https://patchwork.kernel.org/project/netdevbpf/patch/20230220212741.13515-1-puranjay12@gmail.com/
---
tools/lib/bpf/usdt.c | 82 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 82 insertions(+)
diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
index 75b411fc2c77..ef097b882a4d 100644
--- a/tools/lib/bpf/usdt.c
+++ b/tools/lib/bpf/usdt.c
@@ -1505,6 +1505,88 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec
return len;
}
+#elif defined(__arm__)
+
+static int calc_pt_regs_off(const char *reg_name)
+{
+ int reg_num;
+
+ if (sscanf(reg_name, "r%d", ®_num) == 1) {
+ if (reg_num >= 0 && reg_num <= 10)
+ return offsetof(struct pt_regs, uregs[reg_num]);
+ } else if (strcmp(reg_name, "fp") == 0) {
+ return offsetof(struct pt_regs, ARM_fp);
+ } else if (strcmp(reg_name, "ip") == 0) {
+ return offsetof(struct pt_regs, ARM_ip);
+ } else if (strcmp(reg_name, "sp") == 0) {
+ return offsetof(struct pt_regs, ARM_sp);
+ } else if (strcmp(reg_name, "lr") == 0) {
+ return offsetof(struct pt_regs, ARM_lr);
+ } else if (strcmp(reg_name, "pc") == 0) {
+ return offsetof(struct pt_regs, ARM_pc);
+ }
+ pr_warn("usdt: unrecognized register '%s'\n", reg_name);
+ return -ENOENT;
+}
+
+static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
+{
+ char reg_name[16];
+ int arg_sz, len, reg_off;
+ long off;
+
+ if (sscanf(arg_str, " %d @ \[ %15[a-z0-9], #%ld ] %n", &arg_sz, reg_name,
+ &off, &len) == 3) {
+ /* Memory dereference case, e.g., -4@[fp, #96] */
+ arg->arg_type = USDT_ARG_REG_DEREF;
+ arg->val_off = off;
+ reg_off = calc_pt_regs_off(reg_name);
+ if (reg_off < 0)
+ return reg_off;
+ arg->reg_off = reg_off;
+ } else if (sscanf(arg_str, " %d @ \[ %15[a-z0-9] ] %n", &arg_sz, reg_name, &len) == 2) {
+ /* Memory dereference case, e.g., -4@[sp] */
+ arg->arg_type = USDT_ARG_REG_DEREF;
+ arg->val_off = 0;
+ reg_off = calc_pt_regs_off(reg_name);
+ if (reg_off < 0)
+ return reg_off;
+ arg->reg_off = reg_off;
+ } else if (sscanf(arg_str, " %d @ #%ld %n", &arg_sz, &off, &len) == 2) {
+ /* Constant value case, e.g., 4@#5 */
+ arg->arg_type = USDT_ARG_CONST;
+ arg->val_off = off;
+ arg->reg_off = 0;
+ } else if (sscanf(arg_str, " %d @ %15[a-z0-9] %n", &arg_sz, reg_name, &len) == 2) {
+ /* Register read case, e.g., -8@r4 */
+ arg->arg_type = USDT_ARG_REG;
+ arg->val_off = 0;
+ reg_off = calc_pt_regs_off(reg_name);
+ if (reg_off < 0)
+ return reg_off;
+ arg->reg_off = reg_off;
+ } else {
+ pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
+ return -EINVAL;
+ }
+
+ arg->arg_signed = arg_sz < 0;
+ if (arg_sz < 0)
+ arg_sz = -arg_sz;
+
+ switch (arg_sz) {
+ case 1: case 2: case 4: case 8:
+ arg->arg_bitshift = 64 - arg_sz * 8;
+ break;
+ default:
+ pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n",
+ arg_num, arg_str, arg_sz);
+ return -EINVAL;
+ }
+
+ return len;
+}
+
#else
static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
--
2.39.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2 bpf-next] libbpf: usdt arm arg parsing support
2023-03-03 8:37 [PATCH v2 bpf-next] libbpf: usdt arm arg parsing support Puranjay Mohan
@ 2023-03-04 4:22 ` Andrii Nakryiko
2023-03-04 19:18 ` Puranjay Mohan
0 siblings, 1 reply; 4+ messages in thread
From: Andrii Nakryiko @ 2023-03-04 4:22 UTC (permalink / raw)
To: Puranjay Mohan; +Cc: andrii, ast, daniel, martin.lau, song, yhs, bpf, memxor
On Fri, Mar 3, 2023 at 12:37 AM Puranjay Mohan <puranjay12@gmail.com> wrote:
>
> Parsing of USDT arguments is architecture-specific; on arm it is
> relatively easy since registers used are r[0-10], fp, ip, sp, lr,
> pc. Format is slightly different compared to aarch64; forms are
>
> - "size @ [ reg, #offset ]" for dereferences, for example
> "-8 @ [ sp, #76 ]" ; " -4 @ [ sp ]"
> - "size @ reg" for register values; for example
> "-4@r0"
> - "size @ #value" for raw values; for example
> "-8@#1"
>
> Add support for parsing USDT arguments for ARM architecture.
>
> Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
> ---
You don't mention that in the commit message, but how did you test
these changes?
> Changes in V1[1] to V2
> - Resending as V1 shows up as Superseded in patchwork.
>
> [1] https://patchwork.kernel.org/project/netdevbpf/patch/20230220212741.13515-1-puranjay12@gmail.com/
> ---
> tools/lib/bpf/usdt.c | 82 ++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 82 insertions(+)
>
> diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
> index 75b411fc2c77..ef097b882a4d 100644
> --- a/tools/lib/bpf/usdt.c
> +++ b/tools/lib/bpf/usdt.c
> @@ -1505,6 +1505,88 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec
> return len;
> }
>
> +#elif defined(__arm__)
> +
> +static int calc_pt_regs_off(const char *reg_name)
> +{
> + int reg_num;
> +
> + if (sscanf(reg_name, "r%d", ®_num) == 1) {
> + if (reg_num >= 0 && reg_num <= 10)
> + return offsetof(struct pt_regs, uregs[reg_num]);
> + } else if (strcmp(reg_name, "fp") == 0) {
> + return offsetof(struct pt_regs, ARM_fp);
> + } else if (strcmp(reg_name, "ip") == 0) {
> + return offsetof(struct pt_regs, ARM_ip);
> + } else if (strcmp(reg_name, "sp") == 0) {
> + return offsetof(struct pt_regs, ARM_sp);
> + } else if (strcmp(reg_name, "lr") == 0) {
> + return offsetof(struct pt_regs, ARM_lr);
> + } else if (strcmp(reg_name, "pc") == 0) {
> + return offsetof(struct pt_regs, ARM_pc);
> + }
> + pr_warn("usdt: unrecognized register '%s'\n", reg_name);
> + return -ENOENT;
> +}
> +
let's use a more tabular approach, just like, say, riscv does?
> +static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
> +{
> + char reg_name[16];
> + int arg_sz, len, reg_off;
> + long off;
> +
> + if (sscanf(arg_str, " %d @ \[ %15[a-z0-9], #%ld ] %n", &arg_sz, reg_name,
> + &off, &len) == 3) {
if long function call is wrapped, argument on new line should be
aligned with the first argument on previous line. I'd suggest wrapping
right after format string, and start with &arg_sz aligned with arg_str
> + /* Memory dereference case, e.g., -4@[fp, #96] */
> + arg->arg_type = USDT_ARG_REG_DEREF;
> + arg->val_off = off;
> + reg_off = calc_pt_regs_off(reg_name);
> + if (reg_off < 0)
> + return reg_off;
> + arg->reg_off = reg_off;
> + } else if (sscanf(arg_str, " %d @ \[ %15[a-z0-9] ] %n", &arg_sz, reg_name, &len) == 2) {
> + /* Memory dereference case, e.g., -4@[sp] */
> + arg->arg_type = USDT_ARG_REG_DEREF;
> + arg->val_off = 0;
> + reg_off = calc_pt_regs_off(reg_name);
> + if (reg_off < 0)
> + return reg_off;
> + arg->reg_off = reg_off;
> + } else if (sscanf(arg_str, " %d @ #%ld %n", &arg_sz, &off, &len) == 2) {
is the '#<num>' value always in decimal or it could be hex sometimes?
> + /* Constant value case, e.g., 4@#5 */
> + arg->arg_type = USDT_ARG_CONST;
> + arg->val_off = off;
> + arg->reg_off = 0;
> + } else if (sscanf(arg_str, " %d @ %15[a-z0-9] %n", &arg_sz, reg_name, &len) == 2) {
> + /* Register read case, e.g., -8@r4 */
> + arg->arg_type = USDT_ARG_REG;
> + arg->val_off = 0;
> + reg_off = calc_pt_regs_off(reg_name);
> + if (reg_off < 0)
> + return reg_off;
> + arg->reg_off = reg_off;
> + } else {
> + pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
> + return -EINVAL;
> + }
> +
> + arg->arg_signed = arg_sz < 0;
> + if (arg_sz < 0)
> + arg_sz = -arg_sz;
> +
> + switch (arg_sz) {
> + case 1: case 2: case 4: case 8:
> + arg->arg_bitshift = 64 - arg_sz * 8;
> + break;
> + default:
> + pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n",
> + arg_num, arg_str, arg_sz);
> + return -EINVAL;
> + }
This part is repeated verbatim for each architecture, perhaps it's
better to do this post-processing and checking in parse_usdt_spec().
Would you mind adding another patch to your series that refactors
parse_usdt_arg() implementation to fill out struct usdt_arg_spec and
return arg_sz as out parameter. And then parse_usdt_spec() will check
arg_sz, set arg_signed and arg_bitshift parts?
> +
> + return len;
> +}
> +
> #else
>
> static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
> --
> 2.39.1
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2 bpf-next] libbpf: usdt arm arg parsing support
2023-03-04 4:22 ` Andrii Nakryiko
@ 2023-03-04 19:18 ` Puranjay Mohan
2023-03-04 23:34 ` Andrii Nakryiko
0 siblings, 1 reply; 4+ messages in thread
From: Puranjay Mohan @ 2023-03-04 19:18 UTC (permalink / raw)
To: Andrii Nakryiko; +Cc: andrii, ast, daniel, martin.lau, song, yhs, bpf, memxor
Hi Andrii,
On Sat, Mar 4, 2023 at 9:52 AM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Fri, Mar 3, 2023 at 12:37 AM Puranjay Mohan <puranjay12@gmail.com> wrote:
> >
> > Parsing of USDT arguments is architecture-specific; on arm it is
> > relatively easy since registers used are r[0-10], fp, ip, sp, lr,
> > pc. Format is slightly different compared to aarch64; forms are
> >
> > - "size @ [ reg, #offset ]" for dereferences, for example
> > "-8 @ [ sp, #76 ]" ; " -4 @ [ sp ]"
> > - "size @ reg" for register values; for example
> > "-4@r0"
> > - "size @ #value" for raw values; for example
> > "-8@#1"
> >
> > Add support for parsing USDT arguments for ARM architecture.
> >
> > Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
> > ---
>
> You don't mention that in the commit message, but how did you test
> these changes?
I use the QEMU's virt[1] board with cortex-a15 CPU. I take the
libbpf-bootstrap's usdt example[2] and
modify it to attach it to my custom program with
DTRACE_PROBE1/2/3/4... probes to test different combinations.
>
> > Changes in V1[1] to V2
> > - Resending as V1 shows up as Superseded in patchwork.
> >
> > [1] https://patchwork.kernel.org/project/netdevbpf/patch/20230220212741.13515-1-puranjay12@gmail.com/
> > ---
> > tools/lib/bpf/usdt.c | 82 ++++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 82 insertions(+)
> >
> > diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
> > index 75b411fc2c77..ef097b882a4d 100644
> > --- a/tools/lib/bpf/usdt.c
> > +++ b/tools/lib/bpf/usdt.c
> > @@ -1505,6 +1505,88 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec
> > return len;
> > }
> >
> > +#elif defined(__arm__)
> > +
> > +static int calc_pt_regs_off(const char *reg_name)
> > +{
> > + int reg_num;
> > +
> > + if (sscanf(reg_name, "r%d", ®_num) == 1) {
> > + if (reg_num >= 0 && reg_num <= 10)
> > + return offsetof(struct pt_regs, uregs[reg_num]);
> > + } else if (strcmp(reg_name, "fp") == 0) {
> > + return offsetof(struct pt_regs, ARM_fp);
> > + } else if (strcmp(reg_name, "ip") == 0) {
> > + return offsetof(struct pt_regs, ARM_ip);
> > + } else if (strcmp(reg_name, "sp") == 0) {
> > + return offsetof(struct pt_regs, ARM_sp);
> > + } else if (strcmp(reg_name, "lr") == 0) {
> > + return offsetof(struct pt_regs, ARM_lr);
> > + } else if (strcmp(reg_name, "pc") == 0) {
> > + return offsetof(struct pt_regs, ARM_pc);
> > + }
> > + pr_warn("usdt: unrecognized register '%s'\n", reg_name);
> > + return -ENOENT;
> > +}
> > +
>
> let's use a more tabular approach, just like, say, riscv does?
As R0-R10 directly map to uregs[0->10], I used sscanf for that, and as
there are only five named registers
(FP, IP, SP, LR, PC), I thought that using if-else would be good
enough. But I can change it if it is necessary.
>
> > +static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
> > +{
> > + char reg_name[16];
> > + int arg_sz, len, reg_off;
> > + long off;
> > +
> > + if (sscanf(arg_str, " %d @ \[ %15[a-z0-9], #%ld ] %n", &arg_sz, reg_name,
> > + &off, &len) == 3) {
>
> if long function call is wrapped, argument on new line should be
> aligned with the first argument on previous line. I'd suggest wrapping
> right after format string, and start with &arg_sz aligned with arg_str
Will change it in the next version.
>
> > + /* Memory dereference case, e.g., -4@[fp, #96] */
> > + arg->arg_type = USDT_ARG_REG_DEREF;
> > + arg->val_off = off;
> > + reg_off = calc_pt_regs_off(reg_name);
> > + if (reg_off < 0)
> > + return reg_off;
> > + arg->reg_off = reg_off;
> > + } else if (sscanf(arg_str, " %d @ \[ %15[a-z0-9] ] %n", &arg_sz, reg_name, &len) == 2) {
> > + /* Memory dereference case, e.g., -4@[sp] */
> > + arg->arg_type = USDT_ARG_REG_DEREF;
> > + arg->val_off = 0;
> > + reg_off = calc_pt_regs_off(reg_name);
> > + if (reg_off < 0)
> > + return reg_off;
> > + arg->reg_off = reg_off;
> > + } else if (sscanf(arg_str, " %d @ #%ld %n", &arg_sz, &off, &len) == 2) {
>
> is the '#<num>' value always in decimal or it could be hex sometimes?
I have found all these combinations using trying out different things
in my test program as I couldn't
find documentation about this. I could not generate a combination
where a hex value is returned here.
>
> > + /* Constant value case, e.g., 4@#5 */
> > + arg->arg_type = USDT_ARG_CONST;
> > + arg->val_off = off;
> > + arg->reg_off = 0;
> > + } else if (sscanf(arg_str, " %d @ %15[a-z0-9] %n", &arg_sz, reg_name, &len) == 2) {
> > + /* Register read case, e.g., -8@r4 */
> > + arg->arg_type = USDT_ARG_REG;
> > + arg->val_off = 0;
> > + reg_off = calc_pt_regs_off(reg_name);
> > + if (reg_off < 0)
> > + return reg_off;
> > + arg->reg_off = reg_off;
> > + } else {
> > + pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
> > + return -EINVAL;
> > + }
> > +
> > + arg->arg_signed = arg_sz < 0;
> > + if (arg_sz < 0)
> > + arg_sz = -arg_sz;
> > +
> > + switch (arg_sz) {
> > + case 1: case 2: case 4: case 8:
> > + arg->arg_bitshift = 64 - arg_sz * 8;
> > + break;
> > + default:
> > + pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n",
> > + arg_num, arg_str, arg_sz);
> > + return -EINVAL;
> > + }
>
> This part is repeated verbatim for each architecture, perhaps it's
> better to do this post-processing and checking in parse_usdt_spec().
> Would you mind adding another patch to your series that refactors
> parse_usdt_arg() implementation to fill out struct usdt_arg_spec and
> return arg_sz as out parameter. And then parse_usdt_spec() will check
> arg_sz, set arg_signed and arg_bitshift parts?
Sure, I will refactor this in the first patch and then add ARM support
in the second patch.
>
> > +
> > + return len;
> > +}
> > +
> > #else
> >
> > static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
> > --
> > 2.39.1
> >
Thanks,
Puranjay
[1] https://www.qemu.org/docs/master/system/arm/virt.html
[2] https://github.com/libbpf/libbpf-bootstrap/blob/master/examples/c/usdt.bpf.c
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2 bpf-next] libbpf: usdt arm arg parsing support
2023-03-04 19:18 ` Puranjay Mohan
@ 2023-03-04 23:34 ` Andrii Nakryiko
0 siblings, 0 replies; 4+ messages in thread
From: Andrii Nakryiko @ 2023-03-04 23:34 UTC (permalink / raw)
To: Puranjay Mohan; +Cc: andrii, ast, daniel, martin.lau, song, yhs, bpf, memxor
On Sat, Mar 4, 2023 at 11:18 AM Puranjay Mohan <puranjay12@gmail.com> wrote:
>
> Hi Andrii,
>
> On Sat, Mar 4, 2023 at 9:52 AM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
> >
> > On Fri, Mar 3, 2023 at 12:37 AM Puranjay Mohan <puranjay12@gmail.com> wrote:
> > >
> > > Parsing of USDT arguments is architecture-specific; on arm it is
> > > relatively easy since registers used are r[0-10], fp, ip, sp, lr,
> > > pc. Format is slightly different compared to aarch64; forms are
> > >
> > > - "size @ [ reg, #offset ]" for dereferences, for example
> > > "-8 @ [ sp, #76 ]" ; " -4 @ [ sp ]"
> > > - "size @ reg" for register values; for example
> > > "-4@r0"
> > > - "size @ #value" for raw values; for example
> > > "-8@#1"
> > >
> > > Add support for parsing USDT arguments for ARM architecture.
> > >
> > > Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
> > > ---
> >
> > You don't mention that in the commit message, but how did you test
> > these changes?
>
> I use the QEMU's virt[1] board with cortex-a15 CPU. I take the
> libbpf-bootstrap's usdt example[2] and
> modify it to attach it to my custom program with
> DTRACE_PROBE1/2/3/4... probes to test different combinations.
>
Nice, please mention that in the commit message. We don't have 32-bit
arm tests in CI, so explicitly mentioning manual testing is good to
have.
> >
> > > Changes in V1[1] to V2
> > > - Resending as V1 shows up as Superseded in patchwork.
> > >
> > > [1] https://patchwork.kernel.org/project/netdevbpf/patch/20230220212741.13515-1-puranjay12@gmail.com/
> > > ---
> > > tools/lib/bpf/usdt.c | 82 ++++++++++++++++++++++++++++++++++++++++++++
> > > 1 file changed, 82 insertions(+)
> > >
> > > diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
> > > index 75b411fc2c77..ef097b882a4d 100644
> > > --- a/tools/lib/bpf/usdt.c
> > > +++ b/tools/lib/bpf/usdt.c
> > > @@ -1505,6 +1505,88 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec
> > > return len;
> > > }
> > >
> > > +#elif defined(__arm__)
> > > +
> > > +static int calc_pt_regs_off(const char *reg_name)
> > > +{
> > > + int reg_num;
> > > +
> > > + if (sscanf(reg_name, "r%d", ®_num) == 1) {
> > > + if (reg_num >= 0 && reg_num <= 10)
> > > + return offsetof(struct pt_regs, uregs[reg_num]);
> > > + } else if (strcmp(reg_name, "fp") == 0) {
> > > + return offsetof(struct pt_regs, ARM_fp);
> > > + } else if (strcmp(reg_name, "ip") == 0) {
> > > + return offsetof(struct pt_regs, ARM_ip);
> > > + } else if (strcmp(reg_name, "sp") == 0) {
> > > + return offsetof(struct pt_regs, ARM_sp);
> > > + } else if (strcmp(reg_name, "lr") == 0) {
> > > + return offsetof(struct pt_regs, ARM_lr);
> > > + } else if (strcmp(reg_name, "pc") == 0) {
> > > + return offsetof(struct pt_regs, ARM_pc);
> > > + }
> > > + pr_warn("usdt: unrecognized register '%s'\n", reg_name);
> > > + return -ENOENT;
> > > +}
> > > +
> >
> > let's use a more tabular approach, just like, say, riscv does?
>
> As R0-R10 directly map to uregs[0->10], I used sscanf for that, and as
> there are only five named registers
> (FP, IP, SP, LR, PC), I thought that using if-else would be good
> enough. But I can change it if it is necessary.
>
let's go with a table approach, it's consistent with riscv, and I find
it easier to follow (even if it's a bit repetitive)
> >
> > > +static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
> > > +{
> > > + char reg_name[16];
> > > + int arg_sz, len, reg_off;
> > > + long off;
> > > +
> > > + if (sscanf(arg_str, " %d @ \[ %15[a-z0-9], #%ld ] %n", &arg_sz, reg_name,
> > > + &off, &len) == 3) {
> >
> > if long function call is wrapped, argument on new line should be
> > aligned with the first argument on previous line. I'd suggest wrapping
> > right after format string, and start with &arg_sz aligned with arg_str
>
> Will change it in the next version.
>
> >
> > > + /* Memory dereference case, e.g., -4@[fp, #96] */
> > > + arg->arg_type = USDT_ARG_REG_DEREF;
> > > + arg->val_off = off;
> > > + reg_off = calc_pt_regs_off(reg_name);
> > > + if (reg_off < 0)
> > > + return reg_off;
> > > + arg->reg_off = reg_off;
> > > + } else if (sscanf(arg_str, " %d @ \[ %15[a-z0-9] ] %n", &arg_sz, reg_name, &len) == 2) {
> > > + /* Memory dereference case, e.g., -4@[sp] */
> > > + arg->arg_type = USDT_ARG_REG_DEREF;
> > > + arg->val_off = 0;
> > > + reg_off = calc_pt_regs_off(reg_name);
> > > + if (reg_off < 0)
> > > + return reg_off;
> > > + arg->reg_off = reg_off;
> > > + } else if (sscanf(arg_str, " %d @ #%ld %n", &arg_sz, &off, &len) == 2) {
> >
> > is the '#<num>' value always in decimal or it could be hex sometimes?
>
> I have found all these combinations using trying out different things
> in my test program as I couldn't
> find documentation about this. I could not generate a combination
> where a hex value is returned here.
ok, that's fine, let's stick to decimal for now
>
> >
> > > + /* Constant value case, e.g., 4@#5 */
> > > + arg->arg_type = USDT_ARG_CONST;
> > > + arg->val_off = off;
> > > + arg->reg_off = 0;
> > > + } else if (sscanf(arg_str, " %d @ %15[a-z0-9] %n", &arg_sz, reg_name, &len) == 2) {
> > > + /* Register read case, e.g., -8@r4 */
> > > + arg->arg_type = USDT_ARG_REG;
> > > + arg->val_off = 0;
> > > + reg_off = calc_pt_regs_off(reg_name);
> > > + if (reg_off < 0)
> > > + return reg_off;
> > > + arg->reg_off = reg_off;
> > > + } else {
> > > + pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
> > > + return -EINVAL;
> > > + }
> > > +
> > > + arg->arg_signed = arg_sz < 0;
> > > + if (arg_sz < 0)
> > > + arg_sz = -arg_sz;
> > > +
> > > + switch (arg_sz) {
> > > + case 1: case 2: case 4: case 8:
> > > + arg->arg_bitshift = 64 - arg_sz * 8;
> > > + break;
> > > + default:
> > > + pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n",
> > > + arg_num, arg_str, arg_sz);
> > > + return -EINVAL;
> > > + }
> >
> > This part is repeated verbatim for each architecture, perhaps it's
> > better to do this post-processing and checking in parse_usdt_spec().
> > Would you mind adding another patch to your series that refactors
> > parse_usdt_arg() implementation to fill out struct usdt_arg_spec and
> > return arg_sz as out parameter. And then parse_usdt_spec() will check
> > arg_sz, set arg_signed and arg_bitshift parts?
>
> Sure, I will refactor this in the first patch and then add ARM support
> in the second patch.
>
sounds good, thanks!
> >
> > > +
> > > + return len;
> > > +}
> > > +
> > > #else
> > >
> > > static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
> > > --
> > > 2.39.1
> > >
>
> Thanks,
> Puranjay
>
> [1] https://www.qemu.org/docs/master/system/arm/virt.html
> [2] https://github.com/libbpf/libbpf-bootstrap/blob/master/examples/c/usdt.bpf.c
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2023-03-04 23:34 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-03-03 8:37 [PATCH v2 bpf-next] libbpf: usdt arm arg parsing support Puranjay Mohan
2023-03-04 4:22 ` Andrii Nakryiko
2023-03-04 19:18 ` Puranjay Mohan
2023-03-04 23:34 ` Andrii Nakryiko
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