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SubjectRe: [PATCH v1 1/4] trace_events: Add trace_print_register to print register fields
On Thu, 11 Apr 2019 16:08:19 -0600
Raul E Rangel <rrangel@chromium.org> wrote:

> This is a hybrid method that combines the functionality of
> trace_print_flags_seq and trace_print_symbols_seq. It supports printing
> bit fields, enum fields, and numeric fields.
>
> Given the following register definition:
> * 0 - Enabled
> * 1 - Width, 0 = 1-bits, 1 = 4-bits
> * 2:3 - DMA, 0 = None, 1 = SDMA, 2 = ADMA, 3 = ADMA2
> * 4:7 - Timeout Counter
>
> The register fields could be defined as follows:
>
> const struct trace_print_field reg[] = {
> {1<<0, "ENABLED"},
> {
> .mask = 1<<1,
> .name = "WIDTH",
> .symbols = (const struct trace_print_flags[]) {
> {0, "1-BIT"},
> {1, "4-BIT"},
> {}
> }
> }, {
> .mask = 3<<2,
> .symbols = (const struct trace_print_flags[]) {
> {0, "NONE"},
> {1, "SDMA"},
> {2, "ADMA"},
> {3, "ADMA2"},
> {}
> }
> },
> {0xF<<4, "TIMEOUT"}
> }
>
> This would print out the following given value 0xAB:
>
> ENABLED: 1 | WIDTH: 4-BIT | ADMA | TIMEOUT: 0xA
>

Note the rational for the __print_symbolic and __print_flags is that
they show how to translate into something that perf and trace-cmd can
read from userspace.

How does perf or trace-cmd parse this? To add something like this, you
need them to have the same output as what is displayed by the trace
file otherwise NAK.

-- Steve


> See https://pastebin.com/x73d5cvL for this in action.
>
> Signed-off-by: Raul E Rangel <rrangel@chromium.org>
> ---
>
> include/linux/trace_events.h | 4 ++
> include/linux/tracepoint-defs.h | 6 ++
> include/trace/trace_events.h | 9 +++
> kernel/trace/trace_output.c | 121 ++++++++++++++++++++++++++++++++
> 4 files changed, 140 insertions(+)
>
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index 8a62731673f7..3c44909ce8b3 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -23,6 +23,10 @@ const char *trace_print_flags_seq(struct trace_seq *p, const char *delim,
> const char *trace_print_symbols_seq(struct trace_seq *p, unsigned long val,
> const struct trace_print_flags *symbol_array);
>
> +const char *trace_print_register(struct trace_seq *p,
> + const struct trace_print_field fields[],
> + unsigned long val, unsigned long mask);
> +
> #if BITS_PER_LONG == 32
> const char *trace_print_flags_seq_u64(struct trace_seq *p, const char *delim,
> unsigned long long flags,
> diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
> index 49ba9cde7e4b..c3dc27c192f4 100644
> --- a/include/linux/tracepoint-defs.h
> +++ b/include/linux/tracepoint-defs.h
> @@ -16,6 +16,12 @@ struct trace_print_flags {
> const char *name;
> };
>
> +struct trace_print_field {
> + unsigned long mask;
> + const char *name;
> + const struct trace_print_flags *symbols;
> +};
> +
> struct trace_print_flags_u64 {
> unsigned long long mask;
> const char *name;
> diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h
> index 4ecdfe2e3580..6adc32fcb1c3 100644
> --- a/include/trace/trace_events.h
> +++ b/include/trace/trace_events.h
> @@ -300,6 +300,14 @@ TRACE_MAKE_SYSTEM_STR();
> trace_print_symbols_seq(p, value, symbols); \
> })
>
> +#undef __print_register
> +#define __print_register(value, mask, field_array...) \
> + ({ \
> + static const struct trace_print_field fields[] = \
> + { field_array, {} }; \
> + trace_print_register(p, value, mask, fields); \
> + })
> +
> #undef __print_flags_u64
> #undef __print_symbolic_u64
> #if BITS_PER_LONG == 32
> @@ -744,6 +752,7 @@ static inline void ftrace_test_probe_##call(void) \
>
> #undef __print_flags
> #undef __print_symbolic
> +#undef __print_register
> #undef __print_hex
> #undef __print_hex_str
> #undef __get_dynamic_array
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index 54373d93e251..cd5727ad54c3 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -124,6 +124,127 @@ trace_print_symbols_seq(struct trace_seq *p, unsigned long val,
> }
> EXPORT_SYMBOL(trace_print_symbols_seq);
>
> +/**
> + * trace_print_register - Prints all the fields of a register.
> + *
> + * This is a hybrid method that combines the functionality of
> + * trace_print_flags_seq and trace_print_symbols_seq. It supports printing
> + * bit fields, enum fields, and numeric fields.
> + *
> + * Given the following register definition:
> + * * 0 - Enabled
> + * * 1 - Width, 0 = 1-bits, 1 = 4-bits
> + * * 2:3 - DMA, 0 = None, 1 = SDMA, 2 = ADMA, 3 = ADMA2
> + * * 4:7 - Timeout Counter
> + *
> + * The register fields could be defined as follows:
> + *
> + * const struct trace_print_field reg[] = {
> + * {1<<0, "ENABLED"},
> + * {
> + * .mask = 1<<1,
> + * .name = "WIDTH",
> + * .symbols = (const struct trace_print_flags[]) {
> + * {0, "1-BIT"},
> + * {1, "4-BIT"},
> + * {}
> + * }
> + * }, {
> + * .mask = 3<<2,
> + * .symbols = (const struct trace_print_flags[]) {
> + * {0, "NONE"},
> + * {1, "SDMA"},
> + * {2, "ADMA"},
> + * {3, "ADMA2"},
> + * {}
> + * }
> + * },
> + * {0xF<<4, "TIMEOUT"}
> + * }
> + *
> + * This would print out the following given value 0xAB:
> + *
> + * ENABLED: 1 | WIDTH: 4-BIT | ADMA | TIMEOUT: 0xA
> + *
> + * @p: trace buffer
> + * @fields: Array of fields that describe the register. Must be terminated with
> + * an empty value.
> + * @val: register value
> + * @mask: Mask that defines the bits present in @val. Useful if only a subset
> + * of the register was read. Any fields that fall outside of the mask
> + * will not be printed.
> + */
> +const char *trace_print_register(struct trace_seq *p,
> + const struct trace_print_field fields[],
> + unsigned long val, unsigned long mask)
> +{
> + const char *ret = trace_seq_buffer_ptr(p);
> + char *tail;
> + unsigned long fval;
> + int first = 1, symbol_found;
> + const struct trace_print_field *field;
> + const struct trace_print_flags *symbol;
> +
> + for (field = fields; field->mask; field++) {
> + /* Make sure the field mask is within the accessed bits */
> + if ((mask & field->mask) != field->mask)
> + continue;
> +
> + if (!first)
> + trace_seq_puts(p, " | ");
> +
> + first = 0;
> +
> + if (field->name) {
> + trace_seq_puts(p, field->name);
> + trace_seq_puts(p, ": ");
> + }
> +
> + fval = val & field->mask;
> + fval >>= ffs(field->mask) - 1;
> +
> + val &= ~field->mask;
> +
> + symbol_found = 0;
> + for (symbol = field->symbols; symbol && symbol->name;
> + symbol++) {
> + if (symbol->mask != fval)
> + continue;
> + trace_seq_puts(p, symbol->name);
> + symbol_found = 1;
> + break;
> + }
> +
> + if (!symbol_found) {
> + if (fval == 0) {
> + trace_seq_puts(p, "0");
> + } else if (fval == 1) {
> + trace_seq_puts(p, "1");
> + } else {
> + trace_seq_printf(p, "%#x", fval);
> +
> + /* Strip off the null terminator */
> + for (tail = trace_seq_buffer_ptr(p) - 1;
> + tail > ret && !*tail; tail--) {
> + p->seq.len--;
> + }
> + }
> + }
> + }
> +
> + /* Print any left over bits */
> + if (val) {
> + if (!first)
> + trace_seq_puts(p, " | ");
> + trace_seq_printf(p, "%#x", val);
> + }
> +
> + trace_seq_putc(p, 0);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL(trace_print_register);
> +
> #if BITS_PER_LONG == 32
> const char *
> trace_print_flags_seq_u64(struct trace_seq *p, const char *delim,

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